Foundations of Amateur Radio

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Testing a link, on a band, at a time. Dec 27, 2020

Show notes

Foundations of Amateur Radio

The other day I wanted to know what kind of communication was possible between my station and the station of a friend of mine. We want to do some experiments and for that to be possible, we need to have a reliable communication channel.

Traditionally you would get in touch with each other and attempt to find a suitable frequency on a band to make a QSO or contact. That generally involves picking a band, then tuning around the band, finding a frequency that's not in use, then listening, asking if the frequency is in use, then telling your friend via an alternative method where you are, only to have them tell you that they have noise at that particular frequency. You go back and forth a couple of times, finally settle in on a mutually convenient frequency and have a contact whilst keeping note of the signal strength shown on your receiver.

On a good day that will take a few minutes, on a bad day that might take much longer or not work at all.

If you want to do this across multiple bands, you have the fun of doing this whole thing multiple times.

In case you're wondering, I've done this plenty of times and I will confess that it's an interesting combination of joy and frustration in attempting to get the answer to a pretty simple and common question: "Can I talk to my friend?"

In my shack there are plenty of tools, digital multimeters, LC meter, antenna analyser and the like. No doubt you have some or more of those. Perhaps you have an oscilloscope, a vector network analyser, or other gadgets.

None of those are particularly useful tools to solve this particular problem.

On the other hand, you are likely to have a receiver and probably a transmitter. If you're reading or listening to this, you're likely to have a computer as well.

Using a receiver and a computer as a tool to solve this problem might not have occurred to you. It hadn't occurred to me until recently that these are ideally suited for this particular repetitive task.

So, I fired up my copy of WSJT-X and set it to WSPR mode. Changed the band to 2m and set it up to transmit. The other station did the same. Within a couple of minutes the results were coming in. We could both see what the link quality was like between us. Then we changed to 70 cm and did it again. Rinse and repeat for 10m.

As it happens, the other station was receive only and they had to attend to some family activities and I was in my office earning a living, well actually, doing my bookkeeping, but you get the idea, you can do this test while you're doing something else.

I checked in a couple of times to see how it was going when he pointed out that I could see his actual results on the WSPRnet.org website.

I had been looking at the map with mixed results because it had been timing out for most of the day and when it did work, all I could see was that a message was decoded, not how well it was received. Randall VK6WR, the other station, then pointed me at the link to the database which I hadn't seen until then. If you're looking, it's at the top right.

Out pops a list of all the WSPR spots his station reported, and as a bonus, the spots reported by another local amateur.

If you know me at all it will come as no surprise that I used the opportunity to make a chart. Actually I made several, one showing the frequency drift between our stations, one showing the signal strength.

Between the three bands it looks like 2m gives us the best opportunity for experimentation, though 70cm does appear to have some possibilities. Sadly 10m isn't with the antennas currently in the air, but I saw an email the other day with reports of a new vertical at the other end, so we'll have a go at doing the 10m test again in the very near future, perhaps even today.

Right now from the WSPRnet.org website I'm downloading this month's WSPR reports from the Downloads section to see who else saw my signals. No doubt I'll make a chart or six. I'll keep you posted.

I must thank Randall VK6WR for pointing me at the database link on the WSPRnet.org website, because that made propagation and link testing so much more useful and repeatable.

Tools come in all shapes and sizes. What's one that unexpectedly helped you lately?

I'm Onno VK6FLAB

When will it ever end? Dec 20, 2020

Show notes

Foundations of Amateur Radio

Mark Twain is often misquoted in relation to reports about his death, pithy as always, he said: "The report of my death was an exaggeration." Similarly the death of amateur radio has been reported on many different occasions.

Letting amateurs near a Morse key, banning spark-gap transmitters, introducing transistors, integrated circuits, computers, the internet, software defined radio, the list grows as technology evolves. I can imagine our descendants decrying the death of amateur radio with the commodification of quantum computing at some point in the future of humanity.

Yesterday I had an entertaining and instructional play date with a fellow amateur. We discussed countless aspects of our hobby, things like how you'd go about direction finding if you had access to multiple radios and antennas, what characteristics that might have, what you'd need in the way of mathematics, how you'd write software to solve the problem and how you'd go about calibrating such a system. Could you use a local AM broadcast station as a calibration source, or do you need to generate a known signal?

We started talking about how you'd send data across the network so you could have a dozen devices in different locations that you could synchronise and share data. How would you control it, how would you make use of existing standards, were there other tools like this already and what were their limitations.

Then there was the conversation about using spectrum effectively, seeing current digital modes like FT8 and their level of effective use of a 2.5kHz slice of spectrum with 15 second time-slots and the theoretical bandwidth that you might achieve if you used that mode as a data transmission mode.

There was the conversation around how you'd use propagation tools to determine path openings on the higher bands without needing a beacon, just a computer and a radio.

Then we talked about how you'd go about making a simple WSPR beacon, based on a minimum component count and some readily available hardware, rather than a sophisticated transceiver like a PlutoSDR.

There was a discussion around E-class amplifiers and their characteristics and potential pitfalls.

We managed to cover a fair bit of ground in a few hours over our hot beverage of choice, a nice meal for lunch and despite me tripping over the threshold of my front door, banging my head against the wall and rolling my ankle. The head is fine, the ankle not so much.

My point is that the world of amateur radio is never done, it's never finished, there's never an end. There's always more to discover, more to explore, build and investigate.

How on earth could you contemplate that this was a hobby that had no relevance in the world today, let alone that of tomorrow.

I for one am very happy to call myself an amateur and looking forward to discovering what else there is to play with. Why are you an amateur and does this feel like the end or a new beginning every day?

The reports of the death of amateur radio was an exaggeration.

I'm Onno VK6FLAB

If you want to do HF in an apartment, where do you start? Dec 13, 2020

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Foundations of Amateur Radio

One of the many vexing issues associated with getting on-air and making noise is actually making that happen.

So, let's look at a completely restricted environment. An apartment building, seven stories off the ground, no ability to make holes, an unsympathetic council, restrictive local home owners association, et cetera, et cetera.

On the face of it your amateur radio hobby is doomed from the start.

In reality, it's only just beginning.

So, to hear HF right now, today, you can go online and listen to a plethora of web-based software defined radios. There's the canonical WebSDR in Twente and a whole host of others using the same or similar software. There's KiwiSDR, AirSpy, Global Tuners, and many more.

This will give you countless radios to play with, coverage across the globe, the ability to compare signals from different receivers at the same time on the same frequency, the ability to decode digital modes, find propagation, learn about how contests are done, the sky's the limit. I'll add that you don't need an amateur license for many of these resources, so if you're considering becoming part of the community of radio amateurs, this is a great way to dip your toe in the water. Think of it as a short-wave listening experience on steroids.

I hear you say, but that's not amateur radio.

To that I say, actually, it is. It's everything except a physical antenna at your shack or the ability to transmit.

Permit me a digression to the higher bands. If you want to listen to local repeaters on UHF and VHF, listen to DMR and Brandmeister, you'll find plenty of online resources as well. You can often use a hand-held radio to connect to a local repeater which can get you onto the global Echolink, IRLP and AllStar networks. Failing that, there's phone apps to make that connection instead.

Of course if you want to expand your repertoire to transmission, beyond a hand-held, you can.

There are online transmitters as well. Many clubs have their club station available for amateurs to use remotely using a tool like Remote Hams. You'll get access to a radio that's able to transmit and you'll be able to make contacts, even do digital modes and contests. You will require an amateur license and access to such a station. Some clubs will require that you pay towards the running of such a service and often you'll need to be a member.

Then there's actually going to the club, you know, physically, going to the club shack and twiddling physical knobs, though for plenty of clubs that's now also a computer since they're adopting software defined radios just like the rest of the community is. Using a radio via a computer can be achieved directly in the shack, but there's no reason to stay on-site. You can often use these radios from the comfort of your own shack.

If you do want to get physical with your own gear, receiving is pretty simple. A radio with a wire attached to it will get you listening to the local environment. I have for example a Raspberry Pi connected to an RTL-SDR dongle that's connected to a wire antenna in my shack. It's listening across the bands 24/7 and reporting on what it hears.

If you want to use an actual transceiver and you don't have the ability to set-up an antenna, kit out your car and go mobile. Failing that, make a go-kit with batteries, which as an aside will stand you in good stead during an emergency. Take your go-kit camping, or climbing, or hiking. Plenty of opportunities to get on-air and make noise.

I hear you asking, what about having an antenna farm?

Well, you can set one up in a farmers paddock and connect to it remotely - you will need permission from the land-owner - there's plenty of amateurs who use their country abode as a remote station.

If you want to make noise at your actual shack, the antenna might be a piece of wire hanging from the balcony after dark, or an antenna clamped to the railing. You can use a magnetic loop inside your house. Some enterprising amateurs have tuned up the gutters in their building, or made a flagpole vertical, or laid a coax antenna on the roof. Have a look for stealth antennas, there's a hundred years of amateurs facing the same problem.

My own station is very minimalist. There's literally a vertical antenna clamped to the steel patio. Using that I'm working the world with 5 Watts, 14,000 km on 10m, no kidding.

Getting on-air and making noise doesn't have to start and finish with a Yagi on a tower. There's plenty of other opportunities to be an active amateur.

I'm Onno VK6FLAB

2m reciprocity and other assumptions Dec 06, 2020

Show notes

Foundations of Amateur Radio

Over the past nine and a half years I've been hosting a weekly radio net for new and returning amateurs. Called F-troop, it runs every Saturday morning at 0:00 UTC for an hour. Feel free to join in. The website is at http://ftroop.vk6flab.com.

In making the better part of six thousand contacts during that time I've learnt a few things about how nets work and how there are built-in assumptions about how a contact is made. There are several things that seem universally accepted that are not actually supported by the evidence and repeating them to new amateurs is unhelpful.

For example, there is an assumption that on 2m there is signal reciprocity. By that I mean, what you hear is what the other party hears. On HF, contrary to popular belief, this is also not universally true due to massive power and antenna differences and signal reports on FT8 bear that out - for example, my signal is often reported at least 9 dB weaker than the other station.

The reason that on 2m this isn't the case is because in general there is at least one other transmitter involved, the repeater. If you're joining in via a remote network, either via RF or via the Internet, there are even more times when this isn't true, but let's stay with the simple scenario of a single repeater and two stations.

If I'm using a base-station with a fixed antenna, my connection to the repeater is rock-solid. If you are using a hand-held and you're on the move, your connection to the repeater is anyone's guess. It could be great, it could be poor or even non-existent.

Not only that, the repeater is often using higher power, sometimes much higher. On average the repeaters near me are using 30 Watts, the highest uses four times that, the lowest uses 10 Watts. In contrast, a handheld uses at most 5 Watts, but more likely than not, half that.

Receiving a strong signal on a hand-held is simple, transmitting a weak signal to a repeater is not.

The point is, you might be hearing me as-if I'm sitting next to you, but I might be hearing you on the other end of a really scratchy and poor, intermittent and interrupted link.

If you add other repeaters and links with differing volume or gain settings to the mix, you get the idea that a 2m conversation may in many ways act like a HF contact.

That implies that there are plenty of times when you should use phonetics to spell your callsign and anything else of interest, despite the often repeated assertion that you don't use phonetics on 2m.

Another assumption is that 2m is less formal than HF. The people you talk to on 2m are likely to be local, perhaps people you've met at a HAMfest, face-to-face. You recognise their voice, you know their situation, their station and their habits.

On HF however, you have contact with people across the globe, most of whom you've never met, will never meet, have no idea about, let alone have a relationship with. That's not to say that you cannot have a friend on HF, I have plenty of people whom I speak with on HF, often during a contest, whom I've never met, but whom I speak with regularly on air. I can similarly recognise their voice, their callsign and know what to expect.

The point is that the more you look at the differences between 2m and HF, the more you realise that they are the same. Interestingly, as an aside, a contact on 10m or 15m can on plenty of occasions sound like a strong local FM contact.

My advice is to not think of 2m as a "special" band, but to think of it as an amateur band with a set of conditions. By law you are required to announce your callsign every ten minutes and at the beginning and the end of each contact. Note that this doesn't mean at the beginning and end of each over. In case that doesn't make sense to you, a contact is the whole conversation from start to end. Each time a station transmits during that contact is an over.

You should vary how you identify yourself, using phonetics or not, at the minimum required interval, or on every over, depending on the circumstances, not depending on the band.

Look forward to making contact with you on what ever band. You can get in touch via email, cq@vk6flab.com is my address and if you're into Morse, this podcast is also available as a Morse-code audio file.

I'm Onno VK6FLAB

Prior Planning Prevents Poor Performance Nov 29, 2020

Show notes

Foundations of Amateur Radio

The other day I was adding an item to my to-do list. The purpose of this list is to keep track of the things in my life that I'm interested in investigating or need to do or get to finish a project. My to-do list is like those of most of my fellow travellers, unending, unrelenting and never completed. As I tick off a completed item, three more get added and the list grows.

Given some spare time and to be honest, who has that, I am just as likely to find an item on my to-do list that was put there yesterday as an item that was put there 10 years ago. Seriously, as I migrate from platform to platform, my to-do list comes with me and it still has items on it that haven't been done in a decade, let alone describe what project it was for.

Of course I could just delete items older than x, but deciding what x should be is a challenge that I'm not yet willing to attack.

Anyway, I was adding an item to the list when I remembered seeing something interesting on the shed wall of a fellow amateur. There were two pieces of printed paper with a list of to-do items on it. Looking pretty much like my to-do list, except for one salient detail.

Each to-do list was for a different project.

At the time I spotted it I smiled quietly to myself and thought, yep, keeping track is getting harder for everyone.

Bubbling away in the back of my mind this notion of a to-do list for a single project kept nagging at me. Yesterday it occurred to me why it was nagging.

If you have a to-do list for every project then once the project is done, the to-do list is done. Not only that, the items on a project to-do list don't really grow in the same way as an unconstrained to-do list does.

It also has a few other benefits.

The sense of satisfaction towards completing a project is amplified as each item is ticked off and ultimately the project is done.

I'm sure that project managers already know this, might even have a name and a process for it. No doubt there are aspects that I've not considered, like for example, the never ending range of projects or the trap of a miscellaneous catch-all project, but I'll cross those bridges when I run into them.

As of right now, this gives me an improvement on my stifling life to-do list and it brings great satisfaction when I can tick off a whole project.

No doubt you've gotten to this point wondering what this has to do with amateur radio?

If it hasn't occurred to you, consider what's involved into setting up a portable power supply for when you activate on a field-day, what you need do to get logging working, what needs to happen to get ready for a contest, what you need to do when you're selecting your next radio, how you're going to prepare for the park activation next week and so-on.

If you have insights into this, feel free to get in touch. cq@vk6flab.com is my address. Speaking of me, did you know that "Foundations of Amateur Radio" is a weekly podcast and that we're up to episode 285? If you haven't already and you're itching to get your hands on even more content, before episode 1 there was another podcast, "What use is an F-call?"

It has 206 episodes and other than the name and my youthful self, the content is more amateur radio. If I've done everything right there won't be much in the way of overlap in those 491 episodes, other than the same unrelenting quest for new and exciting things to do with Amateur Radio, but then you already knew that.

Now where's my podcast to-do list?

* Tell you about "What use is an F-call?", tick. * Tell you that I'm nearly at 500 episodes, tick. * Finish recording this episode, tick.

I'm Onno VK6FLAB

When one WSPR receiver just isn't enough Nov 22, 2020

Show notes

Foundations of Amateur Radio

When one WSPR receiver just isn't enough

The other day during a radio play date, highly recommended activity, getting together with friends, playing radio, seeing what you can learn, we were set-up in a park to do some testing. The idea was an extension on something that I've spoken about previously, using WSPR, Weak Signal Propagation Reporter, to test the capabilities of your station.

If you're not familiar with WSPR, it's a tool that uses your radio to receive digital signals from WSPR beacons across the radio spectrum. Your station receives a signal, decodes it and then reports what it heard to a central database. The same software can also be used to turn your station into a beacon, but in our case all we wanted was to receive.

If you leave the software running for a while you can hear stations across many bands all over the globe. You'll be able to learn what signal levels you can hear, in which direction and determine if there are any directions or bands that you can receive better than any other.

We set up this tool in a park using a laptop, a wire antenna and a radio running off a battery. In and of itself this is not particularly remarkable, it's something that has been done on a regular basis all over the globe, and it's something that I've been doing on-and-off for a few years.

What made this adventure different is that we were set-up portable about a kilometre up the road from the shack, whilst leaving the main WSPR receiver running with a permanent antenna.

This gave us two parallel streams of data from two receivers under our control, using different antennas in slightly different conditions, within the same grid-square, for the purpose of directly comparing the data between the two.

Over a couple of hours of data gathering we decoded 186 digital signals, pretty much evenly split between the two receivers. More importantly, the stations we heard were the same stations at the same time which gave us the ability to compare the two decoded signals to each other.

One of the aspects of using WSPR is that it decodes the information sent by a beacon. That information contains the transmitter power, the grid locator and the callsign. After the signal is decoded, the software calculates what the signal to noise ratio was of the information and records that, additionally giving you a distance and direction for each beacon for that particular transmission.

I created a chart that showed what the difference was between the two, plotted against the direction in which we heard the decode. This means that you can compare which antenna can hear what in which direction in direct comparison against the other.

In telling this story another friend pointed out that the same technique could be used to compare a horizontal vs. a vertical antenna, even compare multiple bands at the same time.

It looks like I might have to go and get myself a few more RTL-SDR dongles to do some more testing. If you don't have a spare device, there's also the option of comparing other WSPR stations that share a local grid square, so you can see what other people near you can hear and if you like, use it as an opportunity to investigate what antenna system they're using.

WSPR is a very interesting tool and putting it to use for more than just listening to a band is something that I'd recommend you consider. I've already created a stand-alone raspberry pi project which you can download from GitHub if you're itching to get started.

Thank you to Randall VK6WR for continuing to play and to Colin VK6FITN for expanding on an already excellent idea. If you would like to get in touch, please do, cq@vk6flab.com is my address.

I'm Onno VK6FLAB

For that one special event ... Nov 15, 2020

Show notes

Foundations of Amateur Radio

Radio amateurs like to do new things, celebrate, remember, bring attention to, and overall have fun, any excuse to get on air. One of the things that we as a community do is setup our radios in weird and wonderful places, on boats, near light-houses, on top of mountains, in parks, you name it.

Another thing we do is create special callsigns to mark an occasion, any occasion.

For example, to mark the first time the then Western Australian Chief Scientist, Professor Lyn Beazley was on air she used the callsign VI6PROF.

When Wally VK6YS (SK) went on the air to educate the public about Rotary's End Polio Now campaign, he used VI6POLIO. More recently the Australian Rotarians of Amateur Radio operated VK65PFA, Polio Free Africa. When it's active, you'll find VA3FIRE to remind you of Fire Prevention Week in Canada, the Chinese Radio Amateurs Club operates B0CRA through to B9CRA which you can contact during the first week of May each year as part of the Chinese 5.5 Ham Festival.

We create callsigns for other things too.

Datta VU2DSI commemorates November 30th, the birthday of Indian physicist Sir Jagadish Chandra Bose named by the IEEE as one of the fathers of radio science, by operating a special callsign AU2JCB in his honour for a couple of weeks around the end of November.

I mention this because it's not hard to achieve. It's called a "Special Event Callsign" and many if not all amateur licensing authorities have provision for such a callsign. Rules differ from country to country, some say that the callsign must be for something of special significance to the amateur community, others require that it's of national or international significance. In Canada for example, if you're celebrating an anniversary, it must be a minimum of a 25th increment.

Different countries have different formats.

The USA for example issues temporary one by one calls consisting of a letter followed by a digit followed by a letter.

The UK offers GB and a digit followed by two or three letters. There's also "Special" Special Event Stations, which can have a format like GB100RSGB.

In Canada there's a whole system based on what kind of event, what region it's significant to, who's operating it, and so on.

In the Netherlands you can have a normal prefix followed by at most eight characters and an overall maximum length of twelve characters and you can have it for at most a year and only one at a time.

In Germany you can use a standard callsign pattern with a four to seven character suffix, but only for a limited time.

In Australia there's the traditional VI and a digit followed by any number of characters, but remember if you make it massive, getting it in the log is not always easy and using a digital mode like FT8 might not work as expected.

What ever you want to commemorate, celebrate or bring attention to, remember that your callsign is only one part of the process. Consider who's going to actually operate the callsign, if you're going to issue QSL cards, if there are awards or a contest associated with the callsign, if there needs to be a website, if this is a regular thing, or a once-off.

Another thing you need to consider is how you're going to publicise this callsign. There's no point in going to the effort of obtaining a special event callsign with nobody knowing about it, that's the whole point.

No matter which way you jump, there's always a large range of special event callsigns on the air at any one time and making contact with one is often a massive thrill for the person operating the callsign, not to mention the person making the contact.

So, if you have a chance to have a go, I'd encourage you to get on air with a special event callsign and make some noise!

I'm Onno VK6FLAB

It lives ... crystal radio with three components Nov 08, 2020

Show notes

Foundations of Amateur Radio

The idea of building a crystal radio occurred to me a little while ago. I committed to building one, supplies permitting, before the end of the year. I can report that I now have a crystal radio. It works, as-in, I can hear a local AM broadcast station, and it took a grand total of three components costing a whopping two and a half bucks.

Before I get into it, this isn't glorious AM stereo, or even glorious AM mono, this is scratchy, discernible, unfiltered, temperamental radio, but I built it myself, from scratch and it worked first time.

Before I start describing what I did and how, I'm letting you know in advance that I'm not going to tell you which specific components to buy, since your electronics store is not likely to have the same components which would make it hard for you to figure out what would be a solid alternative if you didn't understand the how and why of it all.

So, disclaimer out of the way, my aim was to build a crystal radio using off the shelf components without needing to steal a razor blade, shave a cat, sharpen a pencil or any number of other weird contraptions. Not that those aren't potentially interesting as life pursuits, though the cats I know might object strongly, I wanted this to be about learning how this thing actually works without distraction.

I set about finding a capacitor and an inductor combination that made a resonant circuit with a frequency range that falls within the AM broadcast band. If you recall, you can make a high-pass filter from either a capacitor or an inductor. Similarly, you can make a low-pass filter from either component. If you line up their characteristics just so, you'll end up with a band-pass filter that lets the AM broadcast band pass through.

Now notice that I said range.

That means that there needs to be something that you can adjust.

In our case you can either adjust the inductor, or the capacitor, technically you could do both. My electronics store doesn't have variable inductors, so I opted for a variable capacitor.

The challenge becomes, which variable capacitor do you select with which inductor?

I used a spreadsheet to show what the bottom and the top range for each capacitor would be if combined with each inductor. This gave me a table showing a couple of combinations that gave me a range of resonance inside the AM band.

The formula you're looking for is the resonant frequency for a parallel LC circuit. Take the inductance and multiply that by the capacitance, then take the square root, multiply it by pi and again by two, then take the inverse and you'll have the resonant frequency. You'll need to pay attention to microhenry vs millihenry, and picofarad vs nanofarad and you'll also need to confirm that you've got kHz, MHz or just Hz out the other end, otherwise you'll end up several orders of magnitude in the wrong spot.

If you do all that, you'll likely end up with a couple combinations of inductor and capacitor that will do what you want.

Then when you head to the electronics store, you'll find that the stock you're looking for is end-of-life and that the colour coding on them isn't right, but if you manage to navigate that swamp, you'll come out the other end with a few parts in your hands.

Final bit you'll need is a diode. It acts as a so-called envelope detector. I'm not getting into it here, I'll leave that for another time, but a Schottky or Germanium diode is likely going to give you the best results for this experiment.

Wiring this contraption is pretty trivial. Start with joining the inductor and capacitor to each other in parallel, they'll act as the LC circuit. You can change the resonance by tweaking the variable capacitor. Then attach a long antenna wire to one end and an earth wire to the other end. Finally, connect the diode and an amplified loudspeaker in series between the LC antenna end and the LC earth end and your radio is done.

For my experiment the loudspeaker has a built-in amplifier, it's an external PC speaker with a power supply. I also had to keep my hand on the antenna to create enough signal - since essentially I'm a large body of water - great for being a surrogate antenna.

The unexpected thrill of hearing a local announcer coming through into my shack from three components lying on my desk was worth the anticipation. Highly recommended.

What are you waiting for?

I'm Onno VK6FLAB

The excitement is palpable ... Nov 01, 2020

Show notes

Foundations of Amateur Radio

I'm looking at components. Not looking for, looking at. I have them sitting on the bench in front of me. A collection of six variable capacitors and six inductors. There's also a germanium diode, a breadboard, some connecting wires and two connectors.

I don't quite need that many capacitors or inductors and truth be told a breadboard is overkill, but I found myself getting into the spirit of things and for the tiny investment it seems like the thing to get whilst you're dipping your toe into the art of electronic circuit prototyping.

I am noticing something odd whilst I'm looking at these components, a familiar feeling in some ways, butterflies in my stomach. It's the exact same feeling as when I sit at the radio, getting ready to speak into the microphone just as I am starting a weekly radio net, something that I've now done about 480 times, not to mention the times when I did around 1600 interviews or broadcast live to the world, butterflies.

I'm mentioning this because in many ways this is a momentous event, not for the world, not for humanity, not even for the hobby, but for me. It's the first time I'm building a circuit completely from scratch, no pre-made circuit board, no pre-selected components, no building instructions, just me, some resonance formulas and the hope that I've understood what they represent and that the components I selected will do what my calculations say they should.

To make this even less exciting, there's no external power, nothing that's going to go boom or let magic smoke escape, nothing that will break if I get it wrong, but still.

The other day I received an email from Phil, WF3W. We have been exchanging email for a couple of years now. He's a member of the Mt Airy VHF Radio Club in Pennsylvania in the United States.

His email outlined an interesting question. What do new amateurs get excited about in this era of the ubiquitous world wide web? As a hobby we're attracting new members every day. Many of those are coming to the community by way of social media, rather than using things that are more traditionally considered radio like HF DX, making long distance contact using HF radio, rather than exchanging pithy emails or instant messages via the interconnectedness of the globe encompassing behemoth of the Internet.

The answer came easily to me, since last week we had a new amateur, Dave VK6DM who made his very first long distance HF contact between Australia and the United States. His level of excitement was contagious and that's something that I've found happens regularly.

Someone talks about magnetic loop antennas and the next thing six amateurs are building them. One person starts playing with satellites and before you know it YAGIs are being built and people are describing their adventures.

The same is true with my crystal radio. I've talked about it a couple of times and people are digging out their old kits and telling stories about how they grew up with their dad making a crystal radio.

That's what is exciting the new amateurs. The internet is just an excuse to find each other, just like F-troop is an excuse for people to turn on their communications tool of choice at midnight UTC on a Saturday morning to talk about amateur radio for an hour.

My excitement comes from trying new things and just like keying a microphone for the first time, there's this almost visceral experience of anticipation associated with starting.

I'm still working out how I want to build my new toy and how to go about testing to see if it actually works and what to look for if it doesn't. I'm trying hard to resist tooling up with crazy tools like signal generators and oscilloscopes, instead opting to use things I already have, like LC meters and my ears.

I can't wait until I can share how it goes.

I'm Onno VK6FLAB

Antenna testing in the field. Oct 25, 2020

Show notes

Foundations of Amateur Radio

Antenna testing in the field.

If you've been around amateur radio for any time at all, you'll know that we spend an awful lot of time talking about antennas. How they work, where to get them, how to build them, how strong they are, how cheap they are, how effective, how resonant, you name it, we have a discussion about it.

It might not be immediately obvious why this is the case. An antenna is an antenna, right?

Well ... no.

Just like the infinite variety of cars on the road, the unending choice of mobile phones, ways to cook an egg and clothes to wear to avoid getting wet, antennas are designed and built for a specific purpose. I've talked at length about these variations, but in summary we can alter the dimensions to alter characteristics like frequency responsiveness, gain, weight, cost and a myriad of other parameters.

If we take a step back and look at two antennas, let's say a vertical and a horizontal dipole, we immediately see that the antennas are physically different, even if they're intended for exactly the same frequency range. Leaving cost and construction aside, how do you compare these two antennas in a meaningful way?

In the past I've suggested that you use a coax switch, a device that allows you to switch between two connectors and feed one or the other into your radio.

If you do this, you can select first one antenna, then the other and listen to their differences. If the difference is large enough, you'll be able to hear and some of the time it's absolutely obvious how they differ. You might find that a station on the other side of the planet is much stronger on one antenna than on the other, or that the noise level on one is much higher than the other. Based on the one measurement you might come to the conclusion that one antenna is "better" than the other.

If you did come to this conclusion, I can almost guarantee that you're wrong.

Why can I say this?

Because one of the aspects of the better antenna is dependent on something that you cannot control, the ionosphere, and it is changing all the time.

I have previously suggested that you listen to your antenna over the length of a day and notice how things change, but that is both time consuming and not very repeatable, nor does it give you anything but a fuzzy warm feeling, rather than an at least passing scientific comparison.

A much more effective way is to set up your station, configure it to monitor WSPR, or Weak Signal Propagation Reporter transmissions using one antenna, for say a week, then doing it again with the other antenna.

If you do this for long enough you can gather actual meaningful data to determine how your antenna performs during different conditions. You can use that knowledge to make more reliable choices when you're attempting to make contact with a rare station, or when it's 2 o'clock in the morning and you're trying to get another multiplier for the current contest.

You don't even have to do anything different and spend little or no money on the testing and data gathering.

You can do this with your normal radio and your computer running WSJT-X, or with a single board computer like a raspberry pi and an external DVB-T tuner, a so-called RTL-SDR dongle, or with an all-in-one ready-made piece of hardware that integrates all of this into a single circuit board.

If you want to get really fancy, you can even use automatic antenna switching to change antennas multiple times an hour and see in real-time what is going on.

You also don't have to wait until you have two antennas to compare. You can do this on a field day when you get together with friends who bring their own contraptions to the party.

If there's any doubt in your mind, you can start with a piece of wire sticking out the back of a dongle. I know, I'm looking at one right now. I've been receiving stations across the planet.

One thing I can guarantee is that the more you do this, the better you'll get a feel for how the bands change over time and how to go about selecting the right antenna for the job at the time.

I'm Onno VK6FLAB

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