Podcasts by VK6FLAB
One of the most misunderstood settings on your radio is the microphone gain. You'll often hear people talking about adjusting it up or down depending on what they hear and the results are often displeasing to the ear.
The very first thing to know is that the microphone gain is likely the single most audible setting on your radio, right after the tuning frequency. It's pretty much the first variable between your voice and your transmitter. Set it too low and you'll hear nothing, set it too high and you'll hear gibberish.
I said it's pretty much the first thing, but it's not the very first. That's your voice, unique in all its glory, loud, soft, happy, sad, funny or not, it's the thing that your microphone captures to transmit. Closely coupled to your voice is the distance between your mouth and your mike. The closer you are, the louder, the further, the softer and the more background noise creeps in.
As an aside, speaking of noise, there's background noise at play, but there's also the noise that comes from the audio circuitry itself, which can for example change depending on the temperature of your radio. I'm going to refer to both as noise here, even though they're slightly different.
So, starting with the ideal model where you always speak in the same way, at the same volume, at the same distance from the microphone, with a constant temperature in your radio, at all times, the next thing is the microphone gain, or gain.
Gain is an imperfect attempt at corralling your utterings into electrical signals without causing the audio circuit to distort or drown in noise. Distortion comes as a result of overloading of the audio circuit when the gain is too high, causing clipping, which essentially changes the audio waveform into something that no longer resembles your voice. At the low end of the gain range there is no difference between audio and noise which results in your voice being buried inside a hissing noise.
You might wonder why we don't just build transmitters that cannot clip and increase your volume. Well, we do. We use things like AGC, or Automatic Gain Control to attempt to prevent such things from happening, but this isn't perfect.
All this results in the microphone gain being a setting that you need to tune to your voice and adjust as things change. Overall, the best outcome is when you set the gain so the AGC just engages when you talk normally.
This gain setting also applies to computer generated signals, often fed into your radio via an audio or microphone input. If you set the gain too low, noise is the problem, set it too high and the Automatic Gain Control will distort the signal to the point where it no longer works and causes interference for everyone else including the station that you're trying to contact.
On older radios the output power was fixed. This is also true for Software Defined Radios. To reduce output power, you can change the microphone gain down and reduce the power. Change it to halfway and your output power is essentially reduced to half power. This works for a range of settings, but get too low and we're back to noise and audio fighting each other.
The opposite isn't true.
You cannot increase the microphone gain to increase power. The moment you exceed the audio circuit range your signal is distorted. On an SDR this means that you're exceeding the ability of the Analogue to Digital converter to represent your audio. In digital terms, zero means no sound and all on means 100%. If your audio is so loud as to only be 100% on, that's like sending a tone out the transmitter, resembling anything but your voice.
All of what I've talked about is related to SSB signals and to some extent AM. FM is a different animal entirely. For starters, output power on FM is fixed. The next difference is the signal or channel width. Without going into full detail, FM comes in different widths, WFM or Wideband FM, NFM, or Narrowband FM, and between the two, "normal" FM. To make things more fun, not everyone agrees on what each one means at any given time. Also, channel width and channel spacing are not the same thing, but that's for another day.
Gain aside for a moment, consider two matched FM radios using the same channel width. Your voice volume is determined by how much of the channel you use. Louder means wider, softer means narrower. Adjust the gain up, the signal gets wider, but the limit of the channel width remains, get too high and it clips at the channel width and distorts. At the other end, changing the gain down, you'll use less of the channel width and eventually the noise and your voice will be at the same level and you won't be heard.
Let's look at what happens when you use a normal FM signal to transmit to a narrowband FM receiver. Essentially your signal is too wide and the result is that your voice will be clipped unless you speak really softly or if you've set the gain really low, either way comes with more noise.
Similarly, if you transmit a narrowband FM signal to a normal FM receiver, then your voice will be very low, regardless of the microphone gain setting and turning it up will only distort it due to clipping inside your transmitter.
So, for FM, before fiddling with the gain, make sure that you're using the same FM mode as the other station. One thing to remember is when you use a repeater, if the audio is always too loud for everyone, your mode is probably too narrow. Similarly, if the audio is always too soft and you always need to turn up the volume on your radio, your mode is likely too wide. Check your radio specifications to determine what each mode means.
In broadcast audio this whole thing is managed by calibration using standard tones, but as amateurs we tend to rely on other people reporting their feelings on the quality of your voice with the often heard admonishment to adjust the microphone gain.
I'm Onno VK6FLAB
As a new amateur one of the initial perplexing issues you're confronted with is setting up your first radio to talk to the local repeater. The question is so common that it's almost an invisible rite of passage to a new licensee. While I'm a fan of learning, there is plenty of that to go round and setting up your radio to talk to a repeater shouldn't be a hurdle to getting on air and making noise.
Ignoring the whole repeater thing for a moment, let's consider your radio. It doesn't matter if it's a handheld, a base station, a boat anchor or something else. To participate in the whole repeater experience, you need to tune your radio to hear it.
Technically, if I told you that you could tune to a local repeater on 146.750 MHz, that would be enough information to get you going, but this depends entirely on a set of standard assumptions that are likely not obvious to you. Let's explore what's going on.
Given that frequency, you can set your radio to 146.750 MHz and in most cases, you'll be able to hear the repeater. To actually participate, you would need to do some more work to get your transmitter to be heard.
As I said, standards are what makes that possible, but like every human endeavour, caution must be applied. As Andrew Tanenbaum said: "The nice thing about standards is that you have so many to choose from." With that in mind, let's proceed. Before you start yelling, I'll add caveats at the end.
Armed with a repeater frequency, you have enough information to get on air, but it assumes that you know a couple of things. So let's delve into those assumptions.
For starters, there is an assumption that you're aware that to operate a repeater you must transmit on a different frequency than what you're listening on. Why that is the case is a whole other discussion which I'll leave for today.
There is the assumption that you know that the two frequencies, one for listening, one for transmitting, are separated from each other by a known distance, a so-called offset.
You're also assumed to know that this offset is fixed but different for each band.
There's more, but let's start here.
For your radio to transmit on a different frequency than you listen, you must tell it to. In many cases tuning your radio to a so-called repeater frequency will already do this for you, but not always.
You might need to specifically program your radio for repeater operation, or turn on the offset mode, or use two memories, or some other thing specific to your radio. Read The Friendly Manual, I know you know how.
The next step is to look at the band you're on. In this case the 2m band. This means that the standard says that the difference between the receive and transmit frequency is 600 kHz. I'm studiously ignoring other bands at this moment because, standards.
At this point you know that your radio should be tuned to 146.750 MHz, it should be in repeater mode and the offset should be 600 kHz. That's when the next question arises, should that be plus 600 or minus 600?
Guess what, another standard. If the receive frequency is less than 147 MHz, the answer is minus 600 kHz. If it's more than 147 MHz, it's plus 600 kHz.
Notice that I didn't specify what happens if it's exactly 147 MHz? That's because nobody knows. Seriously though, the local repeater owner will know, but you can try either and get your answer.
Now for the caveats.
Let's start with the 147 MHz cross-over exception. This isn't global, for example repeaters in California use several different ranges for such a cross-over point.
I also didn't tell you about repeaters on other bands because the offset depends on where you are. In many cases the 70cm repeater offset is 5 MHz, but in Europe it's mostly 7.6 MHz, unless it's 9 MHz. The 10m repeater offsets are often 100 kHz, but sometimes they're 1 MHz, similarly the 6m repeater offset is 1 MHz, except when it's not.
The point being that starting with a receive frequency, there's a great number of assumptions, many of which you'll need to discover for your own location. A great resource which I've mentioned before is the brainchild of Garrett KD6KPC, the repeaterbook.com website and app, maintained by a global group of volunteers, which lists many repeaters and their specific settings, frequencies and locations.
So, armed with this knowledge, I expect that you can now find a local repeater and make use of it. When in doubt, contact the owner and ask for help, they're a friendly bunch. Remember to say thank you!
So, what excuse do you have not to get on air and make noise?
Oh, before I forget, if you don't hear anything, or if transmit isn't doing what you expect, check that you've configured CTCSS, another assumption.
I'm Onno VK6FLAB
The art of amateur radio is a globe spanning activity, held together by radio waves and the promise of a community with a shared uncommon interest. The strength of a community depends entirely on the members of that community. Without the efforts of each individual amateur, our worldwide license to experiment is doomed.
You might ask yourself what part you have to play in this?
Consider what would happen if a group of amateurs decided to transmit on an unlicensed frequency, or purposefully interfered with other legal users. It's obvious that the regulatory response to such illegal activities would be swift and left unchecked, it would spark the end of our hobby.
What prevents that from happening is our common purpose, our common interests, our willingness to address such behaviour, or said in another way, our community standards. It's the thing that keeps us talking, sharing, learning, experimenting and having fun along the way.
I've been told many times that I shouldn't expect all amateurs to be friends, but consider for a moment the sheer diversity of our community. For starters we're scattered around the planet. We have different cultural and political sensibilities, we have different religions and expectations. We don't even speak the same language, even if you forget that the Japanese station you just had a QSO with was using phonetics not even close to their native language.
Those differences are mostly attributes of geography, but they don't end there. We have differences in our households and family structures, our work life and finances, our play time and our interests. We also differ in age, skin colour, gender and even our sexuality, orientation and gender identity.
Even among all those differences, we are still radio amateurs together with our personal preferences for Icom, Yaesu, Kenwood or some other brand, our desire to use QRP or kilowatts, our need to use a Morse key, our voice, or a computer. We choose to use a repeater, or not, choose HF or not, like to chat, or not, build antennas, or not.
So it's with all those differences in mind that I'm distressed to report that yet another amateur has been bullied out of our community. An amateur who joyfully participated in this community, who made videos, wrote software, learnt and shared. Like others I know, she was bullied in our community because she was different and it's not the first time I've witnessed this behaviour and it's not the first time I've called out this unacceptable conduct by so-called members of our community. Different, how you ask? Does it really matter, or are you asking to determine if there was a valid reason for making her feel uncomfortable?
To be clear, our community is a welcoming environment, filled with hope and joy, but there is a small rotten element in our midst that we need to rip out root and branch, much like we would if it was deliberate HF interference.
You might think that given that this abuse exists on reddit, YouTube, Twitter, Facebook, QRZ, email, telephone, letterbox, in clubs and on-air, that it's a majority experience. That's not the case. The same individuals harass fellow amateurs across multiple platforms as entertainment causing untold harm to their victims.
The Standard You Walk Past Is The Standard You Accept. It's not just up to victims of bullying and harassment in a community to speak out. As members of our community, we amateurs have a responsibility to speak out also. Anyone who doesn't is part of the problem. Our community is so diverse as to never be one single thing. A bully is a bully, no matter which words are used to sugar coat it.
I'd like to invite you to consider any bullying you accepted in silence, either personally, as a witness, directly, or indirectly. This community is strong, it's resilient, it's resourceful, it's you and I and it's our duty to stand tall and speak out, loud and proud, about any victimisation.
Even if you've never considered that this is happening in your community, look around and notice people leaving the hobby unexpectedly and examine why that might be the case.
You might ask what it is that you can do to help. For starters, calling it out at every occurrence is part of communicating to the victim that they're not alone. It tells the community that they are part of the solution. It tells the bully that what they're doing is unacceptable.
I host a weekly net where we talk about amateur radio and discuss issues like this as and when they occur. We've done so in the past and will continue to offer a safe space for members of this community.
I have and continue to offer my email address, email@example.com, for anyone who is struggling with this to discuss any bullying that they are dealing with.
I have experienced some of what this amateur has gone through at the hands of this community and I will not stand for it any longer and neither should you. Keeping quiet and changing frequency is not the solution as time after time experience has proven.
Calling out a bully and any bullying behaviour is calling out a vicious minuscule minority with a peanut brain who needs to be read the riot act. They are not welcome in this community. They are few and far between and we really don't need or want them in our midst.
In my opinion, the community must take ownership of this problem and address it directly, rather than sit on the fence and leave a victim wondering why they're on their own. If you are a victim of bullying in this community, I stand with you and if you are a bully, I'll do everything I can to call you out.
I'm Onno VK6FLAB
There are days that my brain just cannot keep up with all the ideas that I have spinning around and today is one such experience. Before I take you on this wild ride I will mention that I'm only going to focus on the amateur radio specific things going on, but I tend to have a couple of projects on the go at any one time, much like a messy desk piled high with paper, books, gadgets, parts and coffee cups, my mind has this sometimes exhausting tendency to see connections between various projects and often this results in deeper rabbit holes, so with that in mind, I'd like to make an attempt at describing all the amateur things that are going on at this very moment.
So, here goes, hang on!
It all started with two friends, independently and until now, unbeknownst to each other, playing with a mode called Digital Radio Mondiale, or DRM. It's something I've talked about before. One friend is trying to decode it, the other is trying to generate it. I'm sitting on the side cheering on because I think that there will come a time when I understand enough of my PlutoSDR that I can create any form of any mode and not be limited to the SSB bandwidth that current technologies use and be able to receive and generate say a 20 kHz DRM signal.
In order to advance my learning, I started the day wanting to describe a PlutoSDR project. I wanted to spend some enjoyable time playing, making some progress and then telling you about it. I did play, I did have fun, I did make progress, but trying to explain precisely what and how was where I came unstuck.
I began describing the difference between analogue and digital radios and how there's a fundamental difference in how a signal comes to exist in both. That quickly turned into a conversation about I/Q signals, a discussion that I've been putting off for a while because I'm still not happy with my own understanding of it, let alone any attempt to explain it to you in a coherent and hopefully fun way.
The complexity of explanation was brought home to me during the week when NASA Administrator Bill Nelson used an example to explain an image taken by the James Webb Space Telescope.
The phrase he used was this:
"if you held a grain of sand on the tip of your finger at arm's length, that is the part of the universe that you're seeing"
That seemed pretty clear to me. I could imagine a grain of sand on my fingertip, extending my arm and grasping the idea that hidden behind it was a small slice of the sky representing how big the image was. For me that explanation was excellent, especially when Bill Nelson went on to say that the things you were seeing were galaxies, each made of a hundred billion stars, each likely with planets in orbit.
Only I discovered that the explanation using a grain of sand wasn't universal. I was surprised to learn that for some it got muddled up with the grains of sand in the universe and the relationship between those and the one on your finger.
To be clear, I'm not saying that there is anything wrong with misunderstanding, but it reminded me in a visceral way that how we explain things matters and there are plenty of times when my own efforts fail to achieve their intended purpose, of making things easier to understand.
Given the importance of I/Q signals within the whole conversation on software defined radios, I don't want to do a half baked attempt and fail. I will say this, an I/Q signal is a way of precisely representing a radio signal, but only to stop you thinking about it further.
I was talking about how my mind accumulates things.
The NanoVNA that's sitting on my desk, gifted to me by a friend, is a fantastic example of the similarity between it, software defined radio and say a TinySA which I came across last week. Let me unpack that a little.
A NanoVNA is a piece of testing equipment, as is a TinySA. They test different things. Both have the ability to generate and measure a signal and in that they share the abilities of an amateur radio transceiver that can also generate and receive a signal.
That right there is a very deep rabbit hole, so I'm going to purposefully step away and continue the journey of observation, only pausing to mention that my PlutoSDR has all the same capabilities and in that it's not alone.
The fundamental difference between these three devices is software. There are a few other things, but on the whole, software.
So, I'm carrying around this mush of things that are almost the same, but different, almost understood, but not quite, almost ready to explain, but not yet.
In an attempt at going forwards by moving sideways, I went on to investigate other things, prompted by people who send me emails. For example, code plugs and DMR and frankly I felt unclean reading the various explanations. I'm a firm believer in Open Source and this is like asking an Icom owner to explain the benefits of using Yaesu hardware.
Another question was around bending antennas, as-in, what happens when you drive down the road and your VHF antenna bends, or what happens if your HF dipole is bent to fit in your garden. Superficially I can say that the antenna changes as its bounding box changes shape. That means that the feed point impedance will change, as will the resonant frequency. The radiation pattern will also be affected, but sitting down and discovering just by how much is going to take more time than I have available whilst attempting to string together some coherent words on a topic I love.
So, in an attempt at telling you what's going on in my world of amateur radio, I leave you with this question:
"What was I talking about again?"
Now I remember, this is about just how complex, fluid and interesting amateur radio is for me and in that observation lies why I'm here doing what I do.
"What makes you keep coming back for more?"
I'm Onno VK6FLAB
In over a decade of writing a weekly article about all manner of different aspects of our hobby and community, I've never once talked about power connectors for your radio. It's so universal as to be invisible and rarely discussed. So much so, that something you do out of habit, makes another stop dead in their tracks and ask themselves why they never thought of it.
Despite how you might feel at the time, there's no such thing as a stupid question. The other day a fellow amateur Dave VK6KV asked about a power connector he'd seen at the local electronics store. That question started a group discussion about powering radios and how best to achieve that.
The very first thing to discuss is that the vast majority of amateur radio transceivers expect a nominal voltage of 13.8 Volt DC. That might sound like a strange requirement, but it's the voltage that comes from a fully charged 12 Volt lead acid battery, which is what many radios use as a power reference.
The next thing to consider is that a transceiver can draw quite a bit of power when it's transmitting. My Yaesu FT-857D user manual suggests 22 Ampere, but I've never seen that in the decade it's been in my possession.
When you purchase a radio, you'll likely discover that it either comes with bare wires, or some random connector that doesn't fit anything else. In many cases I've discovered that people cut off that connector and replace it with whatever standard they've come up with in their shack, but when they take their kit out on a field day, or acquire a new radio, the problem starts all over again.
Let me suggest a different approach.
The Anderson Power company, founded in 1877 by brothers Albert and Johan Anderson in Boston Massachusetts, make a range of connectors called the Anderson Powerpole and they come in a variety of ratings, sizes, shapes and colours.
First introduced as a standard by the ARRL Emergency Communications Course in December of 2000, after previously being adopted by amateur operators in California, the Anderson Powerpole PP15/45 series was selected. The Coordinator for Hawaii State Civil Defense RACES, or Radio Amateur Civil Emergency Service, Ron, then AH6RH, now KH6D has a detailed description on his QSL page on how this came about.
As a result, the stackable, asymmetric, genderless plugs are in wide use within the amateur community. The plugs are designed to be joined together using various orientations, creating a unique connector to suit your purpose. The Amateur Radio Emergency Service or ARES standard is one such orientation and before you adopt the Anderson Powerpole in your shack, make sure you use their orientation to avoid magic smoke from escaping your equipment.
Picking a connector is just step one.
When you acquire a new piece of 12 Volt equipment, you can cut off the connector and replace it with the ARES Anderson Powerpole connector orientation. Many amateurs I know then throw away the unusable connector, or shove it into a box for later.
Instead, what I do is, terminate the plug that you just cut off in exactly the same way. Essentially, from a visual perspective, you've kept the power cable intact, but inserted a Powerpole join into the lead. As a result you now have a standard Powerpole power lead and you have a new Powerpole adaptor to suit the new connector.
For that reason alone, I tend to bring a box of spare Red and Black Powerpole connectors to any field day and use the opportunity to spread the love around.
As I said, the individual plugs come in a variety of colours, I have a selection of eleven in my shack, where for me a different colour means a different voltage or purpose. For example, I've adopted green as the colour for antenna radials.
One challenge I'd not been able to resolve, until suggested by Ben VK6NCB, was how to avoid plugging a 12 Volt power supply into something that expects say 7.5 Volts. Colour alone isn't sufficiently idiot proof, especially in the dark. Ben suggested that I adjust the orientation of the plugs, preventing connectors of different colours to mate. Looking back, I can't understand why I didn't think of that in the decade I've been using them.
I will note that there are other Anderson connectors in use. A popular one is the grey double connector, used in portable solar installations and caravans. I'd recommend that you consider if you really want to plug your radio directly into a solar panel or not and choose your connectors accordingly.
Before you ask, to my knowledge the Anderson Power Company doesn't know I exist, nor did I get compensated in any way to say Anderson Powerpole. It's the ARRL Emergency Services standard and I'm happy to advocate for its use everywhere I go.
So, whether you're using bare wires, banana plugs, Molex connectors or some other random barrel connectors, consider cutting the lead and inserting Anderson Powerpole connectors.
When was the last time that you had to do the 12 Volt connector dance?
I'm Onno VK6FLAB
Not a weekend goes by without an amateur radio contest or six, each with its own objectives, audience, times, rules, exchanges and scores. When you get bitten by the contesting bug, you'll quickly graduate from using pen and paper to keyboard and screen. That process comes with the inevitable selection of software suitable to both run on your shack computer and log your particular contest since as you'll discover, not all software knows about all contests or runs on every computer.
When you eventually do arrive at a working solution, you'll reap the rewards of using technology. Contesting software can help in many different ways. From logging your operating frequency and mode to tracking where other stations are active and it doesn't stop there. Type in a partial callsign and your software can suggest which ones it might be. Log a contact and you'll see if your contact is valid within the rules or not. Software can track your activity level and warn if you're exceeding any contest time limits. It can keep track of multipliers and the impact on your total score and at the end of a contest, contesting software can help with submitting your log.
After you've done this for a while, you'll notice that contest rules and scoring change over time. That brings with it the possibility of your software using old and invalid rules for validation, scoring and other contesting requirements.
In most cases, software is updated manually by the author to implement the latest rules. This means that authors are required to keep up to date with the rules for all of the contests that their software supports, let alone add new contests.
There are a few applications that support the idea of a contest definition which suggests the ability for anyone to define contesting rules to use them within the application. Unfortunately their functionality is strictly limited and they are not sufficient to define every contest rule that is in use today. Sadly, flexible as they might seem, they're neither universal nor compatible with each other. One definition, written by one amateur, for one application, cannot be used anywhere else, never mind trying to determine what the latest version is.
I strongly believe that we need a shared open standard that can serve contest organisers, contest software developers and contest participants. Before I elaborate, I will be explicit in pointing out that the intent is to standardise in a way that makes it possible to document all past, current and future contests and in doing so, provide a collaborative way to share contesting rules between organisers, software developers and contesters, not to mention awards committees and amateur associations.
So, if such a contest rule standard were to exist, what would it look like?
Until now, the approach has been to create a list of keywords and values that deal with particular types of rules, things like band start and stop, zone score, valid prefixes, power level, exchange, etc. The result is a growing but always incomplete list of keywords with no means to define any logic. At the moment, all the contesting applications manage any scoring logic internally, requiring that it's updated when any of the rules change. Not only that, the contest organiser has no insight into the mechanism and no means to validate the process.
As a contest organiser, scoring hundreds if not thousands of logs is a whole different challenge. Many contests do this manually, rely on someone else's software, or if the contest is popular enough, write their own code to manage the process.
All this effort creates a disconnect between the contester, the organiser and the contest software developers, each using their own definition of the rules of any particular contest.
For example, you might define a function that returns the starting and ending time for a contest which gives you a mechanism to detect if the contest is happening right now. A contester could use it to determine when the contest starts and ends, but the same definition could be used by the organiser to determine if a submitted log entry is for a valid time.
Another might be a function that uses a callsign to determine if it attracts points or not and if it does, how many. Contesting software might use it to change the colour of the screen to indicate an invalid entry, but an organiser might use it to exclude a contact from a log.
You could have a function to determine if the exchange is valid, or what the next exchange number is, or if the frequency on which the radio is currently tuned to is allowed for a contest.
You could combine some of these simple rules to determine, for example, if the frequency the radio is on is the same or different since the last contact and if that's permitted or not within the rules.
As long as the framework in which this standard is defined is extensible, any contest could be defined in this way.
If it's written well, contest organisers might be able to write their own rules using this standard and everyone can use the same rules for their own needs.
You might recall that I've spoken about aspects of this problem before and at the time I suggested that an amateur radio standards body would be helpful. Failing that there's nothing stopping a few people collaborating in a discussion about how this might be implemented.
As an IT professional outside my shack I have some ideas on what's needed and what could give the whole amateur community something useful, but unsurprisingly, I don't know everything. Working together as contesters we might come up with a better result. As a starting point, I've created a repository on GitHub called "amateur-contesting-standard" to start a conversation about this scheme and I would love to read your thoughts and see your ideas on how this might be achieved.
If you'd like to get in touch, send an email to firstname.lastname@example.org or find my callsign on Twitter and GitHub.
I'm Onno VK6FLAB
A couple of weeks ago a friend, Ben VK6NCB asked an interesting question in our weekly net. He wanted to know, if money wasn't a concern, what would your ideal shack look like? The answers varied widely from leaving everything as is and using the money to retire, through to purpose built fixed or mobile shacks, with world wide DXCC activation travel and everything in between.
My own answer was a little different. I envisaged establishing an RF research laboratory and spending my life exploring and investigating the ins and outs of the fundamentals of our hobby. Building software defined radios and building tools to leverage their capabilities.
As far-fetched as money not being a concern might sound, it's something that a group of radio amateurs had to grapple with in 2019 when their group came into some money. The result is a private foundation with the aim to support, promote, and enhance amateur radio digital communications and broader communication.
The foundation, Amateur Radio Digital Communications or ARDC uses its resources to provide grants to the amateur community. There's a number of criteria to be eligible to receive an ARDC grant, but you must at least relate to the support and growth of amateur radio, education, research and development. Grants are evaluated on a range of aspirational goals, things like reach, inclusiveness, innovation, social good and others.
One of the first questions you might ask is how did these people get the money and why are they giving it away?
To answer that we'll need to travel back to 1981 when Hank, KA6M had the foresight to imagine that Internet-style networking was going to be a thing and requested a block of IP addresses for use by radio amateurs. If you're not familiar, an IP address is like a telephone number, but for a computer. Hank was granted a block of 16.7 million addresses. For decades these were informally administered by a group of volunteers working under the name of AMPRnet and later 44Net.
In 2011 the group founded ARDC as a California non-profit and officially took ownership of the network space and its management.
At this point I'll make a slight detour into IP addresses. I promise it's relevant.
For information to travel to a computer on the Internet it needs to have an address. That address, originally specified using a 32-bit number, a so-called IPv4 address, made it possible to uniquely identify around 4 billion computers. With the explosive growth of computing and the Internet, the world started running out of addresses and in 1998, IPv6 was proposed to solve the problem. It uses a 128-bit number and has space to uniquely identify something like 340 trillion computers.
In 2018, the ARDC was presented with a unique opportunity to sell some of its increasingly valuable address space, due to IPv4 address scarcity, but soon to be worthless, due to IPv6 adoption. After a year of internal discussion, in the middle of 2019, the decision was finalised and the ARDC sold a quarter of the address block that Hank had been granted back in 1981. On the 18th of July, 2019, Amazon Web Services became the proud new owner of just over 4 million new IP addresses.
I should point out that radio amateurs haven't ever used more than half of the original block and IPv6 is going to make this no longer any issue.
So, how much did they make from this adventure?
Well, each address sold for about $25, making for a lump sum of well over $100 million dollars which the ARDC used to establish its grants program. To round off the story, in 2020, the ARDC changed from a public charity to a private foundation and continues to administer the 44Net and the grants program.
Their grants list is impressive and inspirational, so check it out on the ampr.org website. While you're there, you can subscribe to the newsletter and read about some of the amazing work that's flowing from the ARDC as a result of its efforts.
At this point you might be getting all excited about applying for a grant and you should, but I'd like to ask a different question.
What have you done lately to grow our hobby, to stimulate it, to encourage new people, to innovate, research and learn? What has been your contribution?
So, if you had money, what would you do with your amateur adventure?
I'm Onno VK6FLAB
If you connect the antenna ports of two radios together and transmit from one into the other, that would be bad, right? Just how bad would it be and what could you do differently?
Before I dig in, you might ask yourself why on Earth this question even arises.
Consider having two radios and one antenna. You couldn't use a T-piece to connect two radios to the antenna unless both were receivers. So, after connecting and disconnecting coax for a decade, you might decide to use a two position coaxial switch instead. Set the switch to one port and the first radio is connected to the antenna, flick it to the other port and you've just avoided swapping coax between radios.
I'll point out that in most cases a coaxial switch can be used to connect multiple antennas to one radio, or in reverse, connect multiple radios to one antenna.
When you do start looking for a switch it would be good to test that at no point it connected any two switching ports together, potentially causing the magic smoke to escape from your radio.
A less obvious issue is that a coaxial switch has a property called isolation. It's a measure of what part of a signal leaks between ports and you'll see the isolation or cross-talk of a switch described in decibels or dB.
If you recall, a dB is a relative measure. It means that it's something in comparison with something else, in our case, the amount of signal going into one port compared with the amount of signal leaking through to a disconnected port.
You'd think that in a perfect switch none of the signal would leak through, but it turns out that under different frequencies a switch responds differently, even one specifically designed for switching radio frequencies. It might be that a 1 kHz signal is completely isolated, but a 1 GHz signal is not, which is why when you look at the specifications of a coax switch, you'll see something like "greater than 70 dB isolation at 200 MHz". It's worth noting that the lower the frequency, the higher the isolation, indicating that in the worst case, at 200 MHz, there's 70 dB isolation, but at lower frequencies it has higher isolation, sometimes much higher.
If you were to transmit into this switch with 5 Watts at 200 MHz, the amount of signal that can leak through would be 70 dB less than 5 Watts.
You might recall that you can convert Watts to dBm to allow you to do some interesting calculations. As with other dB scales, it's in comparison to something else, in this case a dBm is in reference to 1 milliwatt and 5 Watts is the equivalent of 37 dBm. This means that if you had a switch with 70 dB isolation, you'd start with a 37 dBm transmission, take 70 dB isolation and end up with a -33 dBm signal leaking through. That's the same as 0.0005 milliwatts. In other words your 5 Watt transmission leaks through your coax switch to the tune of 0.0005 milliwatts.
Is that enough to damage your radio?
Well, that depends on the radio, but let's put some numbers against it.
S9 on VHF and UHF was defined in 1981 as -93 dBm assuming a 50 Ohm impedance of your radio.
So, our leaking signal, -33 dBm, is 60 dB higher than S9. You'd report it as a 60 over 9 contact, a tad excessive, but not unheard of. So by that metric, you should be fine.
Many, but not all, radios specify the maximum radio frequency or RF power that they can handle. For example, according to the documentation, both the NanoVNA and a Icom IC-706 can each handle a 20 dBm or 200 milliwatt signal without doing damage. That means that your -33 dBm signal should't do any damage to those two devices.
I'm off to see what the isolation is for cheap 12V relays to see if I can construct a cost effective, modular, remote control antenna switch with lightning detection.
What are you building next?
I'm Onno VK6FLAB
In the time that I've been a radio amateur not a day has gone by without learning something new. Today was no different and this time learning took me both by surprise and delight. I realise that being delighted by charts, since that's what we're talking about, might not be something that comes naturally, but I can highly recommend that you use this as an opportunity to explore.
So, which specific chart am I referring to?
The venerable Smith Chart, something which I've seen from a distance many times in the past decade, but never actually understood, or to be honest, even looked at with anything more than a glance and a shudder.
My first exploration started with a book published in 1969 by the person who developed the chart, Phillip Hagar Smith, an electronics engineer. The book, over 250 pages, is dense and frankly my reading of the first part of the book did not fill me with delight, but based on what I discovered afterwards, I might revisit it.
The purpose of the Smith chart is to visualise complex mathematical relationships. Instead of filling your worksheet with a litany of calculations, you can draw lines, circles and read the answer straight off the chart.
For example, given the impedance of an antenna system, determining the standing wave ratio becomes a case of putting a dot on a chart, drawing a circle through the dot and reading the VSWR straight off the chart.
It gets better.
If you have a digital Smith chart, like the one shown on a NanoVNA or a RigExpert antenna analyser, you can read the antenna impedance in relation to frequency, use a tuner to change it and see the chart update in real-time in direct response to you changing inductance or capacitance by twiddling the knobs on the tuner.
One of the main things that a Smith chart solves is to visualise a chart with infinity on it, twice. In radio a short-circuit is one extreme and an open-circuit is another. Coming up with a way to show both those conditions on the same chart is a stroke of genius.
The chart has evolved over time, but in essence it's a circle with an amazing set of arcs drawn throughout. The very centre of the chart has the number 1.0 next to it. That's the point at which the VSWR is 1:1, the reactance is zero and it's called the prime centre. A dummy load should show up as a dot in that spot, regardless of frequency.
The Smith chart is normalised. It doesn't matter if you're using a 50 Ohm or a 75 Ohm antenna network system, the middle of the chart is 1.0. Follow the horizontal axis to the right and you'll discover 2.0, that represents twice the resistance. If you're using a 50 Ohm system, 2.0 represents twice that, or 100 Ohm. Go to the left, find 0.5 and that represents half, or 25 Ohm. The far left point on the horizontal axis represents zero Ohm, or a short circuit, the far right represents infinite resistance, or an open circuit.
Positive reactance, or inductance is shown above the horizontal line, negative reactance, or capacitance is shown below the line.
Going back to the middle of the chart, you'll discover a circle. All along that circle the resistance is the same, that is, on a 50 Ohm system, all of that circle represents 50 Ohm. If you look directly above the prime centre, you'll discover another 1.0 on the edge of the chart. The arc coming from that point represents an inductive reactance of 50 Ohm all along its path. Similarly, at the bottom of the chart you'll see an arc coming from a 1.0, representing the capacitive reactance.
Before you pack it in with all this inductive and capacitive reactance, think of it as another attribute of your 50 Ohm antenna system. You don't need to precisely know how it works in order to use it.
Remember how I mentioned that you could just read off the VSWR from the chart?
Drop a point on the chart, anywhere is fine. You can read off both the resistance and reactance following the two arcs through that point. If you draw a circle through the same point with the centre at the middle of the chart, the VSWR of that system is the number that you can read, where your circle crosses the horizontal axis.
Before I go, there are plenty of YouTube videos on the topic, but there are a few that I'd recommend you explore. Among an amazing array of RF educational videos, Rhode and Schwartz made a ten minute presentation called "Understanding the Smith Chart" which walks you through how to read the chart and you don't need the prerequisites to follow along. In Part two of his "Smith Chart Basics" series, Carl Oliver shows how to look up the VSWR in three easy steps and Alan W2AEW has several videos showing the chart in action with several vector network analysers or VNAs and I'd recommend that you look at videos 264 and 314 to get started, but there's plenty more of his handy work to explore.
If you take away anything from this, it should be that the Smith Chart isn't scary, there's just lots of stuff there, but spend a few minutes looking at it and you'll discover just how useful it can be in your day to day amateur antenna tuning adventures.
If you've come across other interesting resources on the topic, don't hesitate to get in touch.
I'm Onno VK6FLAB
It is in my nature to ask questions. It's been hammered into me from an early age and it often brings me new friends, new ideas and new projects. After spending quite some time mulling over my understanding of radio, I came up with this question: "Is it possible to build a single radio transmitter that is capable of emitting a WSPR signal at the same time on all the HF bands?"
Before we look at the hardware, let's contemplate for a moment what this transmission might look like.
Imagine a WSPR transmission as a normal audio signal. It sounds like a couple of warbling tones for two minutes. Unpacking it, the audio signal is about 6 Hz wide and sits somewhere between 1400 and 1600 Hz. If you were to draw a power chart of this, displaying the frequencies horizontally and power vertically, you'd see a completely flat chart with a little spike, 6 Hz wide, somewhere between 1400 and 1600 Hz.
Using an analogue radio, you can play this sound into the microphone or audio port and the radio takes care of transmitting it on the 10m band as a 28 MHz beacon. Tune the radio to 40m and it appears as a 7 MHz transmission.
The two takeaways are that the WSPR signal itself doesn't change between bands or transmissions and the radio does the heavy lifting to make your WSPR transmission come out at the right frequency.
Your radio is moving the audio frequencies to the correct amateur band. The electronics in your radio achieve this move by mixing the audio and the tuning frequencies together.
If you imagine a 28 MHz WSPR signal coming from your transmitter as a power chart, it's essentially silence, except for a little WSPR peak somewhere just off to the right of 28 MHz.
From a mathematical perspective, the frequency mixer in your radio is performing a multiplication and best of all, you don't need a radio to do this. You could use software to multiply frequencies instead and end up with something that represented their product. If you were to create a power chart of this equivalent multiplication, you'd see a completely flat chart with a little spike near 28.1261 MHz.
It gets better.
You can store the result of this calculation in a file as a 28 MHz WSPR signal and you could do this as many times as you want. You could create a file with a 3.5 MHz WSPR signal, one with a 7 MHz one and so-on.
Since we're talking about shuffling numbers only, you could combine all these calculations, and end up with a single file that had several WSPR signals inside it.
The chart picture is again mostly silence, just with little WSPR peaks at frequencies suitable for say transmission on the 80, 40, 15 and 10m bands.
Now all you need is to find a device that's capable of transmitting it.
Turns out that we have such a device. A PlutoSDR, a software defined radio which I've spoken about before. It's capable of transmitting a 56 MHz wide signal, more than ample for what we're doing. We don't need to use the PlutoSDR to calculate the combined signal either, since we can do all that in advance, because as I said, a WSPR signal doesn't change.
So essentially, all we'd need to do is generate a file that has all the WSPR signal information at the right frequencies and send it to the PlutoSDR to transmit.
There are a couple of hurdles to overcome.
When you multiply two frequencies, you end up with two peaks, one at the sum of both frequencies, and one at the difference between them. One you need, the other you don't, so we're going to need to filter this out, something that your analogue radio circuit also does.
Another challenge is around sampling rates. The PlutoSDR needs a specific sampling rate and bit depth, so we're going to have to generate our file just so. I'm going to skip past complex numbers and move on to power output, since all the power from the transmitter will be spread across all of the combined WSPR signals we're attempting to transmit, so we're likely going to need amplification.
There's also the matter of testing before we actually connect this contraption to an antenna and I've glossed over one minor but essential point, the PlutoSDR doesn't do HF.
So, where does this leave us?
We can build a proof of concept using 2m and 70cm. Both those bands are native to the PlutoSDR. I'm currently working on generating the actual WSPR signal file to start the transformation process. A friend has some testing gear that could allow us to see what's coming out of the transmitter without polluting the airwaves and of course, at this point this is all still "What-if". I've not actually made this work, but it's keeping me entertained and that's half the fun.
It gets even better. The Pluto has an FPGA on board, so theoretically at least, we might be able to generate this actual file inside the Pluto in real-time, which opens up a whole other avenue of exploration, but we'll start with crawling before running.
If you have thoughts on this, or any other aspect of the hobby, please get in touch. You can send email to email@example.com or you can find me on Twitter and Reddit with my callsign.
In the meantime, you know the drill. Get on air and make some noise.
I'm Onno VK6FLAB
When you finally get to the point of pushing the talk button on your microphone, after passing the test, receiving your license, getting your radio, building an antenna, digesting the manual, identifying a repeater, untangling its offset, programming those frequencies and keying up, you might be surprised to realise that you're lost for words. Something which I've talked about before.
Even if you do have something to say, finding a person to say it to will be the next big challenge. Truth be told, the more frequencies you have to choose from, the harder it seems to discover a fellow amateur and with Internet connected repeater networks, your choice appears infinite.
So, how do you initiate communication on a repeater? Do you call CQ, ask for a signal check, or just kerplunk the repeater to prove that your signal is getting in?
The very first thing to remember is that you have the exact same rights as every other amateur. No amateur is above any other, though hearing some conversations or responses might give you a different impression.
Before you embark on a long speech, what you need to remember is that your ability to receive is not usually the same as your ability to transmit. If you're using a low-powered hand held radio that's tuned to a local repeater, you might be comparing your little stubby antenna, inside your home, held at an angle, with that of a high power repeater, with a high-gain antenna bolted to a tower installed on the top of a hill. In other words, you can hear the repeater much better than it can hear you.
You'll quickly observe that there are amateurs about who have their radio on all day long and they'll often hear every single transmission that hits the local repeater and even random frequencies. Sometimes this means that you'll have a great friend to talk to, other times it means that you'll have a local troll who in their not so humble opinion determines what is permitted and what's not.
So, to get things rolling, you should follow the KISS principle, an aim championed by the lead engineer of the Lockheed Skunk Works in 1960, Kelly Johnson, "Keep it simple stupid.".
With keeping things simple, there is a fierce and ongoing debate around the use of the phonetic alphabet on a repeater. With the benefit of experience, having run a weekly radio net for over a decade I'm going to be blunt. When you're identifying yourself to the rest of the community, always use phonetics. Only if you've been acknowledged and you're part of the conversation should you even consider dropping your phonetic callsign.
The reason is that your first transmissions will be regularly interrupted by others since they're having a conversation and you'll be butting in. Even if a net controller asks for check-ins, you should use phonetics, since you might not be the only one who keys up at the same time. If you and the controller have known each other for years and they recognise your voice, you could consider dropping the phonetics, but don't expect everyone to know who you are from a single letter getting through. Some people are better at this than others.
Whatever you do, don't barge in with a whole story until you've been acknowledged and the microphone has been handed to you. After all, this is a public shared space.
The next thing to consider is the audience you're talking to. If the repeater is just local, then the people within range are likely to expect your prefix and know who you are, so just your call might suffice, but if you connect to a network, that's not likely to be true. If you want to actually talk to anyone, you can call CQ, but if you just want to let people know you're there, you can say your callsign followed by the word "listening".
If you want to speak with a specific individual on the other hand, you can call them using their phonetic callsign, either with or without the CQ. Also consider they might be on the other side of their shack working hard at attempts to avoid sniffing solder fumes and take a moment to get to the microphone.
In other words, what you say on your repeater depends on what result you want and who else is there. Sometimes there will be a mismatch between the two, just saying your callsign might initiate an hour long conversation, and calling CQ might give you the local troll telling you to go away.
Don't let that dissuade you. Even with years of practice, sometimes the results are unexpected.
Talking on a repeater is like being invited to a party. There are going to be people you know, people you want to know and people you never want to meet again.
So, be considerate, listen more than you talk and be deliberate in your intentions and you'll be fine.
Thanks to Sandip EI7IJB for the question, "What are the rules for calling CQ on a repeater?" If you have other burning questions, get in touch and ask. I'll try to give you a coherent answer.
I'm Onno VK6FLAB
The other day I was woken by the sound of a thunderclap. It was shockingly loud and came out of the blue. A few moments later, it happened again. I exploded out of bed, rushed to the shack, disconnected the beacon power and switched the antenna coax to "safe".
After breathing a sigh of relief, everything went dark and with it came the distinctive sound of the sudden death of the uninterrupted power supply taking with it my workstation.
With nothing else left to do, I reported the outage to the power company, went back to bed, pulled the covers over my head, snuggled in and surprisingly, slept pretty well despite the barrage of water hitting my QTH. The next morning the power was back on and I discovered that one of the residual current devices, the one that powered most, if not all, the wall sockets had tripped. I reset it and much to my surprise, most of my QTH came back to life.
I say most, because after breakfast I had a moment to switch on my radios and see what, if any, damage there was. I could hear and trigger the local repeater, but HF was strangely dead. I could hear the coax switches turning on and off, but the SWR on the antenna was high and it didn't appear that the antenna coupler was doing anything. It's powered remotely using a device called a Bias-T. You use two of them to transport a power supply voltage along your antenna coax. In my case, I inject 12 Volts in my shack, and extract the 12 Volts at the other end near the antenna where it powers the antenna coupler.
Occasionally the antenna coupler needs a reset, so I removed the power, waited a bit and reconnected. Still no response from the coupler, so I disconnected the power and left it for another time.
A few days later I had a moment to investigate further, so I went outside to check out the antenna and coupler. Both looked fine. I removed and reinserted the power, heard a click, but wasn't sure since a car came barrelling down the road at the same time, so tried again and heard nothing.
At this point I decided that this warranted a full investigation and started putting together a mental list of things I'd need. I wanted to test the coupler when it was isolated, I wanted to do a time-domain-reflectometry, or TDR test, to see if anything had changed. This test uses the RF reflection of a cable to determine its overall length and any faults like a cable break, high or low resistance and any joints. If you have a Nano VNA or an antenna analyser, you can do this test. It did occur to me that I didn't have a baseline to compare with, so that was disappointing, but I added it to the list.
First thing to test was to check if the radio had been affected. I turned it on, did the same tests and discovered that the Bias-T was still disconnected, which could explain why I didn't hear a click when I tested a second time. Armed with a level of confidence around power, I tried again to trigger the antenna coupler and got nothing, dread building over the potential loss of a radio in the storm, I set about swapping my HF antenna to another radio.
At this point I was reminded of an incident, 37 years ago, as a high school student during a class outing. My wonderful and inspirational physics teacher, Bart Vrijdaghs, took us to the local University where the head of the Physics Department of the University of Leiden gave us a tour of their facilities. He took us into a student lab full of oscilloscopes and tone generators and set-up a demonstration to show us how you could generate Lissajous figures. He was having some trouble making it work and with the impertinence reserved for teenagers I quoted a then popular IBM advertisement from 1985, "Of Je Stopt de Stekker Er In", which loosely translates to asking if he had plugged it in.
I can tell you, if looks could kill, I wouldn't be telling this story.
Suffice to say, it wasn't. Plugged in, that is.
Back to my HF antenna.
Yeah. It was already plugged into the other radio, so, unsurprisingly it was unable to send any RF to, or from, the first radio, much like some of the advanced telepathic printers I've had the pleasure of fixing during my help desk days a quarter of a century ago.
After all that, I can tell you that HF seems to work as expected. The beacon is back online and I have some work ahead of me to create some baseline TDR plots and perhaps a check-in, check-out board to keep track of what's plugged in where.
That and looking for another UPS, since keeping the computer it's connected to up and running, at least long enough to properly shut down, would be good.
What other lessons can you take away from lightning hitting nearby?
I'm Onno VK6FLAB
When you obtain your license there's a whole lot of learning to be had before you even get started with your first transmission, but when you get there you'll discover that learning has just begun and the rest of your life will be beset with challenges, quests, discovery and dawning understanding.
One of the early and recurring questions is around the best time to be on air. Before I get into the why, the answer is, right now.
This interminable question will continue to haunt you throughout your life, and the most pressing answer will be shaped around the missed opportunity. You'll discover tools that assist with predicting propagation, web-sites that explain what the various layers of the ionosphere do and how they affect your ability to use radio to make contact with other amateurs.
There's learned discussion around testing and tracking propagation, special modes that help create your own maps for your own station and you'll discover an endless supply of experts who will advise you when you should power up your transceiver and call CQ.
Whilst I've only been an amateur for a short time. In the decade to date I've learnt one thing about propagation. Despite all the tools, the discussion, the maps and forecasts, there is no substitute for actually getting on air and making noise. Over the past while I've been watching the propagation from my own shack using a 200 milliwatt beacon and I've discovered that running 24 hours a day, every day, well, almost every day, my signal gets to places far beyond my wildest dreams.
I have also discovered trends. That is, the average distance of the signal reports is increasing over time. This isn't a linear thing, not even a recurring thing, much like the ebb and flow of the tides, varying from day to day, a little bit at a time, inexorably making your shoes wet when you least expect it.
While to some extent we've tamed the prediction of the tides with complex and interrelated cycles, discovered by using Fourier transforms, we're no-where near achieving this level of sophistication for the ionosphere and its associated propagation.
Just like predicting a specific wave is still beyond the capabilities of a tide table, predicting the ability of a radio wave to make it from your antenna to that of another amateur is beyond any tool we have today.
Another way to look at predicting the complexity associated with the ionosphere is comparing it to weather forecasting. We have national forecasting bodies, with millions of sensors, super computing cycles that dwarf most other research, a global network of satellite sensors, roughly a quarter of which have some form of earth sensing capability, transmitting terrabytes of data every day and still we cannot determine where on Earth it's going to rain tomorrow.
The ionosphere, whilst it's being monitored, is not nearly as well resourced. It's not nearly as visible to the average person as the packing of an umbrella and the political perception of need is nowehere near as urgent as getting the weather right.
So, absent accurate forecasting, finding a better way to determine when to get on air is required. That said, I've discovered that regret is the biggest motivator to get on air. The day after a contest when a friend made a contact with an amazing station, or the lunch break where I didn't power the radio on to discover a random opening to a clamouring horde of calls looking to make contact.
So, my best advice to you is to get on air whenever you can. You might not make a contact every time, but you'll discover what the bands look like right now and you'll have the chance of hitting the jackpot with a rare contact and truth be told, I think your chances of making a contact are higher than winning the lottery.
When you do take that step, you'll start discovering the ebb and flow of the bands, discover the characteristic sound that each band makes and what a band sounds like when it's open and when it's not. You'll hear stations far and wide, discover that while there are trends in propagation, there are no rules. From one moment to the next, you'll discover the thrill of hearing something unexpected.
One thing to consider, if you get on air for the sole purpose to make contacts, you're likely going to be disappointed. It's like fishing. Most people don't get up at some crazy hour, sit on a damp jetty, freezing parts of their anatomy off for the sole purpose of catching fish.
So, get on air and make some noise, today.
I'm Onno VK6FLAB
In our hobby we regularly invoke line of sight when we discuss the VHF and higher bands. It's a simple concept to help describe when two transceivers can hear each other. The process evokes an image of a beam of light travelling unobstructed between the antennas at either end. Some might picture a laser, others a flashlight, both are useful to become familiar with some of the concepts.
If there's a pole between the two, a laser beam, unless it's particularly powerful, won't go through to the other side. A flashlight beam on the other hand might fit around the pole and still be visible at the destination. That illustrates that objects can get in the way of a signal, reducing strength and sometimes blocking it entirely, but it's not the only effect at play.
Imagine a building with a mirror glued to its side. If you shine a laser at an angle at the mirror, you can reflect the light off the mirror and essentially still land on target. This is useful if you want to avoid an obstacle directly between you and your destination.
The reflected light travels a different and slightly longer distance than direct light would, but if there's no obstacles, both will arrive at the destination.
This is an example of a multipath, where the same signal arrives at its destination using multiple different paths.
If you've ever used HF radio, making a contact on the other side of the planet, it should come as no surprise that radio waves travel in more than just straight lines. Depending on frequency, radio waves can be affected by phenomena like ionospheric reflection and refraction, atmospheric ducting and even bounce off water, the ground, mountains, hills and objects like buildings, aircraft and even water droplets, along their path.
Each of these cause a radio signal to take multiple paths to arrive at the destination.
It gets better.
A radio signal that travels along a different path takes a measurable difference in time to get to its destination when compared with another path for the same signal. From a radio signal perspective, this difference in time is also known as a phase shift.
Now consider a single radio signal that travels along two paths, just like our laser beam and mirror. If you imagine a radio signal as a sine wave, you can draw the two signals on the same chart. They will be in lock-step with each other, since they're the same radio signal, but they won't be on the same place on the chart. In relation to each other they'll be shifted along the time axis, since one took longer than the other to get to the destination.
At the destination, the receiver hears a combination of both those signals. They're added together. That means that what's sent and what's received are not the same thing and why it's a great idea to use phonetics in radio communications. In some cases the two signals help and strengthen each other, they're said to interfere constructively, and sometimes the signals hinder and cancel each other out, or interfere destructively.
Said in another way, a radio signal can arrive at a receiver along multiple paths at the same time. What's heard at the receiver is essentially a cacophony, caused by each slightly different path. Since the signals are essentially all the same, some of these signals reinforce each other, where some cancel each other out.
This effect isn't absolute, since the different path lengths aren't all exact multiples of the wavelength of the signal, they're all over the place, but there will be groups of paths that help and groups that hinder. This phenomenon was first described by Augustin-Jean Fresnel on the 14th of July, 1816 in relation to light and we now call these groups, Fresnel zones.
Fresnel zones are numbered, one, two, three and up. The first or primary Fresnel zone is the first group of radio signals that helps strengthen the signal, the second zone is the first group of signals that hinders. The third zone is the second group of radio signals that helps and so-on. Odd helps, even hinders.
I should point out that a Fresnel zone is three dimensional. The primary Fresnel zone essentially has the shape of a Zeppelin stretched between the source and the target. The secondary zone is wrapped around the outside of the primary zone like a second skin, but it's thicker in the middle.
In practical terms, what this means in point-to-point radio communications is that your antenna needs to be located in a place where most of the signal arrives. The rule of thumb is that the primary Fresnel zone needs to be at least 60% clear, but ideally 80%.
If you're in a situation where a receiver is moving, say in a car, you can imagine that your antenna is moving in and out of direct line of sight to a transmitter, but it's also moving between the various Fresnel zones. If you were to move your antenna from the first Fresnel zone to the second and then the third, the signal would be strong, then weak, then strong again.
If your receiver is an FM receiver and it's moving from the first zone to the second, it could fall below a threshold and the signal would effectively vanish. Continue to move from the second into the third zone and the signal would sound like it suddenly reappeared as it climbed above the threshold. Do it fast enough and the signal sounds like it's stuttering.
That stuttering has a name. In amateur radio we call it picket fencing or flutter and it's commonly heard in mobile situations on FM transmissions on the VHF and higher bands, but it can be caused by other changes in propagation distance, for example an antenna moving in the wind. The higher the frequency, the less movement is needed to experience this.
To add to the fun of radio, the same threshold effects, actually called the FM capture effect, can be caused by other phenomena, like two stations of similar strength on the same frequency, or interference from the electronics in your vehicle.
And finally, I should point out that the higher the frequency, the smaller the Fresnel zones, and the more susceptible to an object in the path a signal is, but you already knew that, a pole will block a laser beam, but not a 2m conversation on the local repeater.
So, line-of-sight isn't just a straight line, it's a whole lot more fun.
I'm Onno VK6FLAB
The amateur radio community is as varied as humanity across the globe. It represents an endless supply of ideas and experiments that continue to attract people looking for something new and exiting.
On the face of it, our hobby is about radio and electronics, about propagation and antennas, about modes and contacts, but if you limit your outlook to those topics you'll miss out on a vast expanse of opportunity that is only just beginning to emerge.
Until quite recently, computing in amateur radio was essentially limited to logging and contest scoring. It has evolved to include digital modes like PSK31 and the advent of smaller, faster and cheaper computers in the home has brought the possibility of processing unimaginable amounts of data leading to modes like WSPR and FT8.
In the past I've spoken about how amateur radio means different things to different people. Making contact using a digital internet enabled repeater is sacrileges to one and manna from heaven to another. Between those two extremes there is room to move and explore. Similarly where one uses valves, another expects an integrated circuit. One wants low power, the other wants every Watt they can lay their hands on. Contesting versus rag chewing, nets vs contacts, SSB vs. CW, FT8 vs. RTTY. Each of these attracts a different part of the community with different outcomes and expectations. For some it's about antenna building, others going portable, climbing a mountain, or setting up in a park.
Those are all traditional amateur activities, but the choice and opportunity don't end there.
The longer I play with computers the more I see a convergence in the world, a coming together of technologies and techniques. I've talked about some of this before when in 1994 I produced a competition broadcast promotion for the radio station I was working at, using just a computer in the era of reel-to-reel tape and razor blades. My station manager couldn't quite put his finger on what was different, but with hindsight it represented a landslide change in how radio stations have operated since. Mind you, I'm not saying that I was the first, just the first in that particular radio station.
In many ways computing is an abstract effort. When asked, I like to express it as designing something intangible in an imaginary world using an made up language and getting paid real money to make it happen, well, numbers in my bank account at least.
Within that context, amateur radio is slowly beginning to reap the rewards that come from the exponential growth in home computing power. While the majority of humanity might use the vast amount of CPU cycles to scroll through cat videos online, that access to processing power allows us to do other things as well.
For example, right now I'm playing with the dataset that represents all the WSPR spots since March of 2008. As of now there are around four billion rows of contacts, containing data points like a time-stamp, the transmitter, the receiver, the signal strength, location, direction, and more.
As part of that investigation I went looking for documents containing the words "RStudio" and "maidenhead", so I could consider creating a map in my statistical tool that allowed me to represent my dataset. In making that search I discovered a thesis by a mathematician who was using the reverse beacon network in an attempt to predict which station could hear which transmitter at what time.
In reading the thesis, which I opened because I was looking for an example on how to convert a maidenhead locator into geo-spacial data types in R, a popular statistics platform, I discovered that the author didn't appear to have much, if any, amateur knowledge or experience, but they approached their task, attempting to predict as a mathematician what we in our community call propagation, based on a public dataset, downloaded straight from the reverse beacon network, created by amateurs like you and I.
This interaction between science and the amateur community isn't new. Sometimes it's driven by science, other times it's driven by amateur radio. There's a team exploring the ionospheric prediction models that we've used for decades, popularly referred to as VOACAP or Voice of America Coverage Analysis Program, based on multiple evolutions of empirical models of the ionosphere that were first developed in the 1960's, headed by both a scientist and an amateur, Chris KL3WX.
With the advent of WSPR and the associated data collection some experiments have started to compare the reality of propagation as logged by WSPR to the predicted propagation as modelled by VOACAP. One such experiment happened in 2018 where Chris and his team at HAARP, the High-Frequency Active Auroral Research Program, set out to make transmissions at specific times and frequencies, using the amateur community logging of WSPR spots to compare their transmissions to the predictions.
Interestingly they did not match. Just think about that for a moment. The tool we love and use all across our community, VOACAP, doesn't match the reality of propagation.
My own playing with WSPR data is driven by the very same thing that I use to be a better contester, a burning curiosity in all things. My VOACAP prediction experience has been poor to date. Setting up my own WSPR beacon is the first step in attempting to discover what my actual propagation looks like, but in doing so, it's also a possible contribution to the wider challenges of predicting propagation based on a dataset with four billion spots. One such approach might be to create an ionospheric prediction map based on actual data and compare that to the models as well as the published space weather maps and combining these efforts into a machine learning project which might give us the next generation of ionospheric prediction tools, but only time will tell.
No doubt I will have to learn more about statistics and machine learning than I expect, but then, that's half the fun.
So, next time you think of amateur radio as being limited to valves, transistors, soldering, antennas and rag chewing on HF, consider that there might be other aspects to this hobby that you have not yet considered.
What other research are you aware of that relates to amateur radio?
I'm Onno VK6FLAB
The lure of digital modes and the opportunities they bring are enough to tempt some amateurs to begin a journey into integrating their radio and computer to make a new world come to life. This isn't without pain or challenge, but the outcomes are so enticing that many embark on this adventure every day.
As a person who has made this trip it's heart warming to see the joy writ large on the face of an amateur who makes their first FT8 contact on a home brew wire dipole rigged together on a Sunday afternoon to take advantage of the latest opening on the 10m band.
On the flip side, it's heart breaking to see an amateur falter at the first hurdle, attempting to make their computer talk to their radio and giving up because it just won't work. At first this attitude bewildered me in a community of experimenters, but over time I've come to understand that sometimes an analogue approach isn't suited to the digital world. There isn't really a place where you can attach your multimeter and see why the serial connection isn't working, nor is there any universal document that can walk you through how to set things up.
So, for you, if you're in a place where you've all but given up, let me see if I can find words to encourage you to keep trying. I'll skip the propaganda about going digital and move straight to making it work.
This might come as a surprise, but in the digital world, things are built in complex layers of interdependence. Said in another way, using an analogy, to turn on a light you need flick a switch, which depends on power to the switch, which depends on power from the fuse box, which depends on power from the street, which depends on power from the substation and so-on.
If you flick the switch and the light stays off, you need to figure out which part of the chain failed. Did it fail at the bulb or at the substation? If the street is dark, do you need to check the fuse box or the bulb? That's not to say that either, or even both, can also be faulty, but there's no point in checking until the street has power.
From a fault finding perspective, the number of variables that you have control over, in the case of a light bulb not switching on, is strictly limited. You can control the bulb and the fuse and in most cases that's about it, the rest of the chain is outside your direct control.
In attempting to make a computer talk to a radio you can be forgiven in thinking that the level of complexity associated with such a trivial task is just as direct and straightforward. Unfortunately, you'd be wrong. It's not your fault. A popular slogan "Plug and Play" made people think that computers were easy to use and control.
The truth is a far darker reality. One of the hidden sources of frustration in the digital world is the extreme level of complexity. In our quest to standardise and simplify we have built a fragile Jenga tower of software that can collapse at any point. Most of the time this is completely invisible but that doesn't cause it to be any less real. Computers are simple, but only if you control the environment. And when I say control, I mean take ownership of each change.
Updating the operating system? Installing a new application? Adding a new peripheral? Changing location? All these things, innocuous as they might seem, can fundamentally alter the behaviour of your environment.
As an example, consider the location of your device. Let's say that you changed the location of your computer, either physically or via a preference. All of a sudden your Wi-Fi network stops working. The one that you used for years. Turns out that changing location changed the Wi-Fi driver to stop using a particular channel, not permitted in your new location. If you're curious, this happened to me last week.
The point being that troubleshooting is about controlling change in that fragile environment.
So, when you're trying to figure out how to make your serial connection work, you need to stop fiddling with everything all at once and change one thing at a time. Discovering the layers of dependency makes this difficult at times, but not impossible.
For example, a working serial connection requires that both ends are physically connected, speaking the same language at the same speed. That depends on the radio being correctly configured, but it also depends on the computer having the right drivers installed. It also depends on the software you're using being configured correctly to talk to the right serial device and the operating system giving your software permission to do so. It depends on the software using the right radio mode and it depends on the radio being switched on.
Now, imagine the serial connection "not working".
Do you check the radio mode before you check if the radio is turned on?
What about the physical connection?
When you're troubleshooting, you cannot just look at the error message on the screen and follow that path. You need to ensure that all the underlying things are working first. You don't check the bulb until there's light in the street. Same thing. No need to worry about the error until you've discovered that the radio is on, the cable connected correctly, the driver installed correctly, the speeds set right and the mode configured properly. If and only if that's all correct, then look at the error.
This becomes harder if it worked yesterday. What changed between then and now? Did your operating system do an update? Did your radio forget its settings? Did the cat jump on your desk and dislodge a cable overnight? Is there an earth fault that caused the serial connection to cease working?
Sometimes, despite your best efforts, you cannot find the problem.
At that point you need to take a step back and think about how to prove that something is working in the way that you think it is. Multimeter to a light bulb to check continuity - style. In the case of a serial connection, what can you use to test the link if your favourite tool doesn't work or stopped working suddenly?
I've said this before, but it bears repeating, since it's not obvious.
Troubleshooting is all about discovering and controlling change.
Pick one thing to test, prove that it's correct, then pick the next. Eventually you'll come across a "Duh" moment. Don't sweat it, we've all been there. Now do it again!
What's your best troubleshooting moment?
I'm Onno VK6FLAB