The chances are that many of you will have made an FM “bug” style transmitter, a simple one-transistor oscillator usually driven by a small electret microphone. It’s also relatively straightforward to do the same for AM, and if you take a look through AliExpress you’ll find some modules which do just that. [Doz Television Workshop] has one, and he’s treated us to a thorough run-down of its design before addressing some of its shortcomings.
An AM transmitter is simple enough, in this case an oscillator and buffer driving a class C power amplifier. The modulation is applied by a transistor in series with the power amp, driven from an audio amplifier. Some attention has gone into the design of this one, with a proper output filter and plenty of room for tweaking to achieve proper levels and modulation density. There are some problems though — The modulator transistor is mounted upside down for the heatsink, and the frequency stability leaves something to be desired. [Doz] fixes the heatsink mounting and incorporates a DDS frequency synthesizer with an Arduino for control.
More after the break…
The resulting transmitter is better, but there’s still a problem. The limitations of AM broadcasting demanded both limiting and pre-emphasis, which he applies in software through one of the more powerful Teensy boards. We have to admit we’d have tried to do the job the analogue way, but that’s merely preference.
This board looks to be a good solution for an AM radio collector wishing to use their sets in an age of declining AM transmission. It should be legal under Part 15 for Americans, but as he points out it’s not for Brits. We suspect such a low-powered device wouldn’t attract adverse attention though. The video is below the break.
If you don’t need so much quality, it’s possible to do the job in a much less elegant manner.
I never built one of these because where I live you’d need a Amateur Radio license to be allowed to do so. You’d also need that license to attach a proper antenna to a low power device that just had a piece of wire hanging out it’s side. And the local radio amateur community, when asked about how to do any of these things online wasn’t very friendly or helpful to outsiders.
So of course I still fiddled with that antenna, but the “you don’t even get to ask about that because you don’t have the fancy papers I do” kinda put me off ever wanting to get my license. Kind of a bummer. Today there is much more helpful tutorials around for things one may not “technically” be allowed to do, like electrical work. But since people still often do it, educating them (while mentioning the legal situation) is probably better than trying to gatekeep one’s sacred knowledge.
Should have maybe just tried to build a transmitter from one of the radio building books, but the scary stories of a dark van with an antenna on the roof immediately pulling up and fining my parents a lot of money scared kid me off.
You may have a radically different club than mine (entirely possible that your club has prejudiced people), but understand the other side of this: by the time you have put in the work to homebrew a radio, you could have passed all 3 (US) tests and been at the top level of amateur radio for an additional 3% effort and saved 15%+ effort by borrowing tools and knowledge.
I know, because I am an extra. Getting a technician license is super easy. I know how easy it is because I have done it and because I am a volunteer examiner, helping new hams get licensed literally every month. Pass rate is great. Been doing it over a year now.
Now, why the hams are grumbly at you: because we don’t want people doing a negligently crappy job and making a mess of the bands. Hams have been allocated a few niches of the radio spectrum, a shared resource we go to great lengths to keep usable for everyone, and we are charged by the FCC with cleaning up our own messes. (and there are a lot of people deliberately trying to mess stuff up – even in my small town)
A RPi , some software, and a wire can transmit FM – but that signal is dirtier than the city sewer and degrades the shared resource we all have. Plus, we know what transmissions are legal in our country. Sometimes, it’s pretty detailed.
Let us help you build an output filter. Let us check your signal for overmodulation and splatter. Let us loan you our reference material.
And the licensing is part of a commitment to at least try to do a good job. In the end, that’s about all we ask. Free study courses online (I like https://hamstudy.org) the test is $14 at my club.
If someone told you they were planning to defecate on your car, would you pass them a roll of toilet paper?
Seems like a fun project, and I like the use of the Arduino controlled frequency generator board – solves all sorts of problems. As for the ham radio guys you met, those awful crumudgeons are out there, most of them are quite literally dying off, but for every one of them, there’s a dozen decent people. Just gotta find em. There are lots of clubs. The dicks have their club, and they whinge about digital modes during their meetings and how nobody wants to come to the club BBQ, and the nice guys have their clubs.
It’s true however, not many people will AT FIRST be too thrilled with the idea of you making a broadcast frequency transmitter, but anybody with half a brain cell is likely to come around once you explain that you’re not trying to broadcast to the entire room, let alone the city.
Depends where you live but in EU countries have automatic spectrum monitoring stations working 24/7 round the clock. Any attempt at interference with commercial or military frequencies is recorded for later manual analysis.
Recently some pranksters broadcasting emergency signal used to automatically stop trains got caught this way (saved RF monitoring data combined with CCTV recordings)
I don’t think that was technically possible back in the day.
It’s been technically possible for a good few decades, one of the UK radio ham vloggers had a video or two about the remote monitoring stations, might have been RingwayManchester?
+1
Here in Germany we have these spectrum monitoring stations, too.
They record a few hundreds MHz of spectrum in real-time.
The next station I know of is said to be near a technical college in my part of my city. It’s an open secret among hams here.
And it’s not just here since now, but since late 80s/early 90s.
Back then the data was written to high-bandwidth analog medium, I guess?
Nowadays they probably record from 100 KHz to 3 GHz or, I guess?
Here in Germany we have these vans, too.
Back in the 80s, it was yellow though and operated by our federal postal acency (the Deutsche Bundespost, DBP).
It was often to be informally being refered as “der Gilb” (the yellowing/the yellowed, Gilb refers to color yellow/gelb).
Picture: https://tinyurl.com/mr3x4p3z
The vans had high-end scanners, spectrum analyzers of all sorts and antennas mounted on the roof and were searching for illegal transmitters.
Once they showed up, the person responsible not seldomly did make the radio pirate a deal:
Pass an amateur radio exam within a given time and you’ll be forgiven or you get a fine and your equipment will be confiscated.
The confiscating thing was common.
Some illegal equipment was allowed to be possesed, but not to be used.
If it was found out to be used actually (antenna and mike connected), it could be confiscated.
That’s why CBers here got very creative hiding their linear amplifiers. ;)
Because, opening and searching cabinets etc. required a search warrant, it couldn’t be demanded so easily.
Ham radio transceivers were a special case, I vaguely remember.
Listening amateurs, SWLs, without a license were allowed to use them for receive, but mike/key had to be unplugged and the transmitter tubes (the finals) had to be physically removed.
That was in a time when the Yaesu FT-101/Sommerkamp FT-277 was still in wide use.
Nowadays, the vans (now white) still exist but the fiercy Deutsche Post is no more.
The people who are nowdays on duty in this vans are are from the federal network agency and they look for man made noise.
Hams and ordinary citizens can call them for help if they have radio noise in their neighborhood.
They also help hams in legal situations if they have stub born neighbors who refuse to stop using noise makers such as the infamous power line communications (PLC), plasma TVs or noisy solar panel chargers/regulators.
The citizen who is found out to be responsible for the interference must pay a bill for that, um, “investigation”, AFAIK.
“And the local radio amateur community, when asked about how to do any of these things online wasn’t very friendly or helpful to outsiders.’
While arrogant, grouchy, or otherwise unapproachable people do exist in the ham community, percentage-wise, there are no more of them than in any other cross section of humanity.
“…but the ‘you don’t even get to ask about that because you don’t have the fancy papers I do’ kinda put me off ever wanting to get my license.”
I personally have never observed the behavior you describe.
Those ” fancy papers,” by the way, means a person demonstrated some technical knowledge and some understanding of the rules. Some people have to work quite hard to earn their license. I have no doubt your dismissive attitude would ruffle some feathers.
A few thoughts…
If a nasty ham (real or imagined) is enough to discourage you, I’m inclined to think you weren’t all that serious to begin with.
If your local pool of hams really is as bad as you’d have us believe, why bother with them? With an internet connection, the world is your oyster.
Or… maybe the problem is the way you approach others. I’m not alleging that (I don’t know you) but the tone of your remarks suggest you have a chip on your shoulder.
So what would you like to know?
I think the same. Also, hams are very sensitive about black sheep in their own reign.
If someone is unfair to beginners or outsiders, some usually stand up for them and try to lend a helping hand.
Perhaps persuading them to take a ham exam, too.
It’s also a matter of pride and respect. The ham spirit/amateur’s code still means something to most hams.
Those who worked hard for their license do care about reputation of amateur radio.
They try to be acting diplomatic and de-escalating.
What’s unique to amateurs, though, is that they’re from all over society.
Politicians, fishermen, astronauts, kindergardeners, doctors, butchers, musicians, surfers etc.
So a doctor might discuss new equipment or antenna models with, say, a newspaper boy.
Or an astronaut has a casual chat with a granny living with their cats, it’s all possible.
Amateur radio can be really “woke” (diverse) in nowadays terminology, if you will. ;)
That being said, there are of course also groups of hams that regulary meet on local FM repeater as if was a visit in the pub.
They usually don’t like it if a newbie disturbs them.
Again, it’s like with a visit in the pub: There are groups who prefer to be left alone.
Not seldomly them being the stereotypical sad, old men type, talking about ruined marriage, health problems and questionable political views.. ;)
Likewise, CBers used to have “their” channels.
They didn’t like others to show up there, except if they had become friends of their group.
That’s just human, I suppose and not a unique design flaw of amateur radio.
I’m with him. There are plenty nasty (sad) hams out there. When I first was interested I’m ham many years ago, I too was turned off by these gatekeeper people. If you look at any online forum with people asking questions you will find them. There easy to spot. And what ever you do don’t mention the Chinese made radios. They will come to life in a hurry
“I too was turned off by these gatekeeper people…”
Where did this notion come from that the world is obligated to be your private safe-space? I’m turned off by at least half of what appears on the Internet. That doesn’t stop me from using the Internet. I am turned off by jerks on the highway, that doesn’t stop me from driving. I’m turned off by rude store clerks, but that doesn’t stop me from going to the store and buying things.
There are no “gatekeepers” to amateur radio (at least here in the U.S.A.) except for the FCC and a basic set of regulations that applies to everyone.
I’m a VE who has administered successful license exams to hundreds of people, including those as young as 10 years old (little boy), and as old as 85 (a great-grandmother). I guarantee that neither of them has posted to the internet to complain how other people “discouraged” them from becoming hams.
Ironically, the most annoying thing about amateur radio is not the relative handful of grouchy people (I’ve already conceded that they do exist), but the abundance of friendly ones who can’t stop yacking about their latest radio or antenna project.
In the end, some people pursue their interests, while others find excuses not to.
About gatekeeping.. Maybe my wording wasn’t exactly great.
What I’m wondering is, how it comes that people would ever associate terms like “gatekeeping” or “elitism” to amateur radio?
I mean, amateur radio is a hobby, a sub culture, a niche.
It never was mainstream to begin with. 🤷♂️
Radio amateurs used to be a minority, a fine one, still but a minority.
Just like bird watchers, train spotters or nerds and computer geeks had been.
And I can’t recall that nerds, introverts or PDP-8 computer engineers had ever been accused of being elitist or gatekeepers, either. 🤷♂️
So how comes that “gatekeeping” suddenly is such a big thing?
I haven’t even heard about this term until recently.
What’s wrong with society? Be with us or be against us?
What about this socalled “tolerance” everyone talks about since a few years?
Were are rainbows and unicorns if you need them the most? 😟
“gatekeeping” 🙄
Such a nonsense term!
Please define what that even means.
If I tell someone that a vintage NES console needs an equally vintage CRT monitor to look authentic, then it’s “gatekeeping” to some.
Because, a CRT is hard to come by and thus I’m an evil dude because
I’m stating that this piece of rare equipment, which is something you can’t get in a random super market, is necessary.
What a logic! What’s next? Math being rasc*st? 😂
Oh, wait. To some, math is indeed discriminating, because it’s being so absolute. 😟
PS: I love using old radio equipment, too. Is that a problem to you?
If it was the car hobby, then it would be a problem if I’m was into vintage cars from 1950s? 🤷♂️
Seriously, I don’t get it.
Some people are fine eating hamburgers at MCDonalds, some don’t.
Just because these guys prefer quality meals doesn’t mean they’re gatekeeping, right?
Because to some of us, Chinese handheld radios are comparable to fastfood/junkfood.
We don’t have a problem if others eat it, but we may mention health considerations one or two times and decline the offer to join eating politely.
Just as with US fastfood, which may some of us seriously can’t handle (stomach ache, sickness).
The equivalents to health considerations are spurious emissions, for example.
Or use of phase modulation (PM) rather than frequency modulation (FM)
That’s something that modern handheld radios do use, PM.
Because PM can be generated easier than pure FM.
Sure they can be used with FM repeaters and with FM handhelds, but audio quality suffers when mixing FM/PM.
That’s why some hands hold on to vintage radios, also.
The old models were made in times when stricter regulations had been the norm (they use real FM for example).
If they could still buy new high-quality radios, they would consider upgrading.
Unfortunately, companies like STANDARD nolonger exist and the market of amateur radio makers has become small.
I mean the “junk” that Yaesu, Kenwood and Icom produce today doesn’t attract me, at all, either.
And its not about price. Small black boxes are so boring! The whole physical experience is missing!
I mean, where do you can buy an equivalent to an classic Yaesu FT-101 short wave transceiver in a steel cabinet?
With mechanical switches, big VFO and modular design?
The FT-101 cartridge slots are the radio equivalent to PCI Express slots in a PC.
You could take them out, fix them, modify (“hack”) them etc.
By using extension cartridges it was possible to adjust them while the radio was running, even!
So it’s just understandable, I think, that old hams are “stubborn” and keep using their vintage equipment they love.
But people of today seem to twist the whole thing and
make it sound as ui the old operators are “gatekeeping” the hobby,
just because they refuse to use cheap radios like all the young.
Personally, I think that “gatekeeping” really is about the complaining people being jealous.
The young people/beginners of today are angry because they can’t get those vintage radios the old hams tinker with for cheap money and thus enter an inferiority complex.
But that’s not fair, I think.
Just because some people refuse accepting certain new technology that they don’t like doesn’t mean they’re gatekeeping.
They don’t take anyone anything away, after all.
Rather contrary, they would he happy if young people would show interest in their vintage equipment.
Also, they don’t refuse to talk to someone on air if he/she has a Baofeng!?
So what’s the problem here. Each to his own. 73s
There is not a jurisdiction on the planet where an amateur radio license allows you to broadcast on the AM broadcast band. It’s either forbidden, or low power devices are permitted/exempt, and a ham ticket has nothing to do with it.
About that license: I took the U.S. Technician, General and Extra class licenses all in one sitting and I passed them all with flying colors. I have never engaged with the amateur radio community. Never visited a club, never met a ham, never even talked on the radio – “engaged in a QSO” – the irony of which is not lost on me.
So you have convinced yourself that you cannot get into radio building without amateur radio community support, but that’s just nonsense. Every marginally decent library on earth, perhaps outside of North Korea, has the books you need, in case you didn’t have access to the internet, which I think you do, where all the information is available in abundance.
Getting into trouble for building transmitters requires a LOT more effort than getting a license, because unless you build and run a poorly built, seriously high power transmitter, persistently, willfully, that actively messes with commercial operations like cellular, or public safety (say GPS), NOTHING is going to happen, even if you build a modest pirate radio transmitter across the street from the spectrum regulators. So build that little transmitter and learn from it, and move on – license or not.
About amateur radio: if half a day of playing video games, watching a few movies, or doomscrolling on TikTok is a better use of your time than getting an amateur radio license: that’s FINE. Your life, your choices. But I object to the notion that the barrier of entry is high.
I also don’t have a license and been doing radio stuff for years now.
I stick by “Don’t disrupt other stuff” and use approved radios (usually Ti ‘s CC1101 or Hope SX transceivers) on ISM bands.
Probably helps that I am more interested in “stuff” like tpms, RF outlets, garage doors, weather stations and the like.
Honestly, “don’t disrupt the primary spectrum users” is the bottom-line of the regulations you learn about to earn your amateur radio license. The rest is safety and window-dressing.
Exactly. Primary spectrum users either have paid a lot for their slice and have lawyers, or they are the ones with machine guns. Both have making your life miserable in their job descriptions.
To be fair, the U.S. Technician class is perhaps the easiest class all around the globe.
Just a few questions of multiple choice on a paper. It’s doable to anyone with a minimum of common sense, average IQ level and basic understanding of electronics.
By comparison, passing one of our easiest CEPT license exams in Europe is closer to passing General exam in US.
We must be able to answer questions from learning material that spans a hundred pages worth of questions.
We normally spend months of preparation before we attend to the exams.
Our FCC counterparts aren’t present at Disney Land or local carnival, either. ;)
We rather must wait for an appointment in which exams are taken and then travel throughout country to that one office that’s open.
Alternatively, online exams are slowly becoming available, too. Vy73s
Agreed on the extremely unintimidating technician ticket in the U.S., but even the top tier licenses the world over are attainable by anyone with an average amount of intelligence and the patience to read literally one book.
Getting an Extra class license is really not much harder than getting a driver’s license in any Western European country. And to get a driver’s license, you need to travel to a place, run by a government, where they take tests, when they are open, get in line like sheep, and be nice to bureaucrats.
Although I will willingly admit it is easier to get a driver’s license in the U.S. than to pass the Extra class exam. But that bar is so low it could double as a buried radial.
This ^^^
“There is not a jurisdiction on the planet where an amateur radio license allows you to broadcast on the AM broadcast band. It’s either forbidden, or low power devices are permitted/exempt, and a ham ticket has nothing to do with it.”
There are AM nets in the US, who’re using former AM broadcast transmitters.
Also, the band plans have the characters of a “recommendation” rather than a law.
Use of AM is being frowned upon, but not always being forbidden.
The rule of thumb used to be that’s is okay to do unconventional radio experiments,
even if they deviate from the norm, as long as no other operators are being disturbed.
Besides AM fans, there are also fans of eSSB.
That’s SSB with extended bandwidth, for increased audio fidelity and faster digital modes.
Info: http://www.nu9n.com/essb.html
The experimental character of amateurs radio is very important, I think.
In Austria, their national ham club is being called “Versuchssender-Verband”,
which translates to “experimental sender club”.
After all, new modes can only become officially being mentioned in the band plans
after hams had already succesfully experimented with them and gained practical experience from using them.
That’s why even bureaucratic FFC and other telecom agencies had issued special allowances to experimental ham modes,
even if they hadn’t been integrated into official band plans yet.
SSTV had been one of them, I think, way back in the 60s.
PS: I see, “AM broadcast band” means medium wave band here (MW).
The old ordinary, commercial broadcast band, in short.
In Europe that used to be about 525 to 1705 kHz (or about 570 to 175 m wavelength)..
Great video and looks like a nice project. An AliExpress kit is a good way of lowering the threshold of starting with such a project, because low investment in time/money and it’s already working albeit suboptimal. It’s funny that you can expect things like heatsinks the wrong way.
Is there any chance the transistor might be flipped upside down for electrical reasons? Maybe the die paddle is connected to some sensitive node in the circuit (like the modulator output) and this was a cheat to reduce stray capacitance? Normally I would expect something like a ceramic thermal plate between the device and heatsink, adding extra thickness (and cost) beyond an ordinary thermal pad.
Yep, they got the transistor pinout wrong :-) Happens to the best of us. Fixed in next PCB rev!
Noooooo, I’ve never done that before! /s
Just trying to give them the benefit of the doubt!!
I once goofed the PCB footprint for a 100pcs batch of low noise 15W flyback smps – had to solder the coupled inductors onto the bottom side. Nevertheless, it was less PITA to solder other tall components (caps, chokes) on the bottom side too and mount the board bottoms-up than confess a mistake and redesign/reorder the batch of boards.
The other possibility is that the heatsink was intended to be mounted on top of the transistor.
Looks a fun little kit, could make a nice little QRP top band transmitter
You can run a small AM or FM transmiter here in the USA for your home radio projects as long as it falls under the specifications that are outlined under the FCC Part 15 rules and regulations for low power transmitters. I personally have a couple low power AM transmitters that I use with my vintage tube radios.
https://www.fcc.gov/media/radio/low-power-radio-general-information
Digi-Key sells programmable oscillators, that they are happy to program for you in their “value add” department, no Arduino required. They may not output sine-waves though.
Ah … Come back for part 2 where I discuss analogue processing, and build a bit of a prototype. Also there’s a write up on my blog https://andydoz.blogspot.com/2025/01/improving-aliexpress-am-tramnsmitter.html
Thanks for the exposure though. Have a great day. Doz.