No RF gear here?

I've wondered the same thing - I mean wondered whether there was a good forum like this for rf electronics. Once you get addicted to the audio stuff there's only so many amplifiers you can build ! but playing with analogue electronics is fun and there are lots of interesting things to build at the radio end of the spectrum - receivers are a ver rich topic all to themselves. I suspect that the Ham enthusiasts have a good forum or two somewhere.


Edit: you'll recognize my avatar here: http://theradioboard.com/rb/viewtopic.php?f=2&t=4794&hilit=william
 
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There are RF forums. They get the same sort of mix of people as here, with the same mix of truth and error and magic. Antennas and transmission lines are what confuse many DIY RF people, but as here some of them are so confused they don't realise they are confused.

DIY transmitters are fine, but to do it properly you need rather more knowledge than for audio DIY. Safety and interference are bigger issues.

I expect there are pirate radio forums too, where there may be even more error - certainly about legal matters!
 
In the USA, the FCC allows operation of low power FM transmitters, but anything over 100mW must be licensed.

I'm sure most countries have similar restrictions, whether or not they offer licenses would be up to the individual to check with the appropriate ruling body.
 
I've always found Antennas to be a very complex topic and a big enough topic to be dealt with separately from that of the Tx/Rx electronics. Rather like we have a bit of a divide between amplifiers and speakers (transmission lines anyone !). As I think about it, it's an interesting parallel. In audio we try to treat speakers and amplifiers as independent and once in awhile we have to recognize their interdependence. Something similar happens with Ham stuff, where the standard antenna impedances are an attempt to make it easier to design antennas and transmitters separately but in reality there are inter dependencies. Current drive vs voltage drive has it's parallels too. I guess it's all the same in the end!
 
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But seriously interested in making a FM transmitter.... something in the 88 to 109 Mhz band. Around 10 - 50W up the stick.......In the USA, the FCC allows operation of low power FM transmitters, but anything over 100mW must be licensed.

The OP is in Australia. I'm sure that firing up a 50 watt radio station is illegal there too, but I don't know how well such things are enforced.

Pirate radio seemed to come and go several times while I lived in South Florida. While setting up a radio station off shore in a boat would evade prosecution, all the pirates were land based. In fact there was a pirate radio station about a block from my house.

The operator was on the air for over 10 years. He started out with a 17 watt transmitter that covered about a 3 mile circle around his house. He had a 100 watt amplifier for about two years which gave him about 7 miles. Lightning took out the amp, and he never got it fixed. He got his equipment from a mail order outfit in Israel. There was a card that plugged into a PC, a box that sat on top of the PC, and the amplifier when he had it. The box had left and right line level audio inputs which were fed from a small mixing console. The entire setup could be automated in the PC. Radio "shows" could be recorded, or played back from the PC, and a schedule of totally automated operation could be set up. He has a phone number on his web site, and often took live call-ins on the air. He also had live guitar lessons on the air, which I played along with.

One day about 10 years ago, the station was gone. I assumed that the FCC had finally got him, but later I saw his wife in the grocery store and found out that Jack had had a heart attack and died while having Thanksgiving dinner with his parents......Despite what the web site says. The "radio station" is still alive, but now internet only and run by his Miami firefighter friends (his former occupation.

Jack And Jill Radio

DIY transmitters are fine, but to do it properly you need rather more knowledge than for audio DIY. Safety and interference are bigger issues.

ANY transmitter operated on any frequency other that valid amateur radio frequencies in the USA must be "type accepted" by the FCC. Amateur radio transmitters COMMERCIALLY SOLD in the USA must also be "type accepted." This means that a licensed ham radio operator in the USA can build his own radio equipment, and it must meet some spurious and harmonic radiation criteria. Making a bunch of complete radio transceivers and selling them would also require type acceptance, which is a process generally not possible for most DIYers. Radio kits, bare PC boards and accessories fall into a grey zone.

My 41 year career as an RF engineer and transmitter designer at Motorola ended 3 years ago, and the employment agreement preventing me from making RF stuff ended 2 years ago. Will I design and build a "Tubelab style" ham radio? It's on my list. I had a rather complete RF setup on my workbench at Motorola. I have been slowly buying dead RF test equipment cheap on Ebay and fixing it. My plan is to duplicate the setup that I had at work.

I haven't seen an RF forum dealing with advanced RF design, but I haven't really looked either.
 
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Yes, I was not condoning illegal operation but answering the point made that RF transmitters are not really DIY items. They are, but only for those who know what they are doing - which includes staying within the law. For almost everyone that means either fairly low power (almost zero power in the UK) or legitimate amateur radio. It is unlikely that a DIY transmitter for the FM broadcast band with significant power would be legal in almost any country.
 
Ok, distracted today... came to sit in lounge to ask why no diy RF stuff here?

yeahhhh, diyaudio

But seriously interested in making a FM transmitter.... something in the 88 to 109 Mhz band. Around 10 - 50W up the stick.

Any ideas where to find?

Ask some of the guy's transmitting on those frequencies from the upper floors of tower blocks in Birmingham, I've missed them since I moved..........
 
Yes, I was not condoning illegal operation but answering the point made that RF transmitters are not really DIY items. They are, but only for those who know what they are doing - which includes staying within the law. For almost everyone that means either fairly low power (almost zero power in the UK) or legitimate amateur radio. It is unlikely that a DIY transmitter for the FM broadcast band with significant power would be legal in almost any country.

I disagree on the difficulty. I completely agree on the legality.

Look at an old ARRL handbook and it isn't difficult to build a tube based transmitter any where from 750KHz to 220MHz. Above that, get a newer copy and you can go all the way to 1GHz with SS based amps.
 
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Making a bunch of complete radio transceivers and selling them would also require type acceptance, which is a process generally not possible for most DIYers. Radio kits, bare PC boards and accessories fall into a grey zone.
I presume you mean thing like these, often used for (among other things) robot remote control and such. I've got a wireless thermometer that transmits for about one second every 30 seconds in the UHF range. I don't know what output power these things have, I presume they are a lot less than 100mW:
https://www.sparkfun.com/search/results?term=rf

My 41 year career as an RF engineer and transmitter designer at Motorola ended 3 years ago, and the employment agreement preventing me from making RF stuff ended 2 years ago. Will I design and build a "Tubelab style" ham radio? It's on my list. I had a rather complete RF setup on my workbench at Motorola. I have been slowly buying dead RF test equipment cheap on Ebay and fixing it. My plan is to duplicate the setup that I had at work.

I haven't seen an RF forum dealing with advanced RF design, but I haven't really looked either.
I don't know much about RF design (learning more is an item on a long list of things I want to do), but obviously part of the problem with doing it is the exponential cost of test equipment for it.

After so many decades ago when my father tried to teach me Morse code, I finally got my amateur license five years ago. It was a ham cram to get people technicians licenses, and I passed the tech, general and extra tests all in one go. That was largely from having a career doing (non-RF) electronic design and embedded programming, as well as my father's influence of having been a ham.

I knew an RF designer at work a few years ago, it seemed what he mainly did was order parts from MiniCircuits and put them together with the fancy RF interconnects, though I'm sure he had a lot of experience from before those things were available (he talked about how much easier things were with the MiniCircuits things than in the old days), and a lot of knowledge about which components to buy and how to connect them.

The ARRL puts out a magazine named QEX (in addition to the standard QST magazine that all ARRL members receive) that only has articles on designing and building homebrew amateur equipment. I've found a couple copies at hamfests, it looks really interesting to me, I don't know how the articles would compare with your experience, but it looks like a good resource for anyone interested in RF design.
 
The OP is in Australia. I'm sure that firing up a 50 watt radio station is illegal there too, but I don't know how well such things are enforced.
.....
The operator was on the air for over 10 years. He started out with a 17 watt transmitter that covered about a 3 mile circle around his house.
.....
He got his equipment from a mail order outfit in Israel. There was a card that plugged into a PC, a box that sat on top of the PC, and the amplifier when he had it.
.....
The entire setup could be automated in the PC.
.....

Thats interesting recall of the past, and akin to my 'want and need'.
My past experience in the field was in the mid 70's as a ratbag on 27MHz band, so I have a basic recall of SWR etc..... interference... and somewhat 'misspent youth'.
None of us were 'legal' as such and some were using up to 100W linear amps in the rig.
A lot of the technical expertise for equipment repair, additional PPL Chanel's and output power mods was provided by sympathetic HAM operators who realised some of us would pursue careers in the field or join their ranks... and that we all weren't evil, punk, anarchistic ratbags out to cause mayhem.
There was always the myth of being raided by the 'powers that be', but this only ever happened when other pirates fought over territory. It's a bit difficult to hide a decent 1/4 or 1/2 wave ground plane stick in the air mounted on a home or car.

Crazy days indeed. Now...

I've had 'need' due to an ongoing 'problem' yet to be remedied, but this is forward planning to address the issue by "an means necessary" should other means fail. Think, 'neighbor from hell generating an equal opposite reaction'.

Automation fits the plan, start operation upon reaching an audible noise level threshold.

I must admit my own limitations and the 'mail order' of equipment is the only practical start, but critical to effectiveness relates to the magical 'black art' of antenna design. The ideal configuration would be highly focused directional and efficient within a certain bandwidth [say 100 to 107MHz].
 
None of us were 'legal' as such and some were using up to 100W linear amps in the rig.....Crazy days indeed.

Back when Smokey was chasing the Bandit all over the television screen I might have taken the tube from a scrap laser (a 4PR400, closely related to the 4-400) and operated it far beyond its ratings to push the wattmeter somewhere beyond 1200 watt. That thing ran about 3 KV and scared the bleep out of me, so I gave it away to a guy who would never use it.

Still I could barely talk to friend about 20 miles away who was running a Gates shortwave broadcasting transmitter on 11 meters. There were just too many "good buddies" on the air then and I had an interstate road in my backyard.

I found 3 old pictures from back then, 2 of me wiring up his Gates TX, and one of me holding up a fluorescent bulb near the antenna on his car....there was a Collins TX in the back seat.

Yes, I did go get my Tech license in the early 80's, which eventually became an Extra, and I experimented with EME (moonbounce) before the "powers that be" (City Code Enforcement) made my antennas go away.

The ARRL puts out a magazine named QEX

We had them in out library at work. Even non hams would read them for current tech.

MiniCircuits and put them together with the fancy RF interconnects

MiniCircuits did more to lower the barrier to entry for RF than anyone else. I used their stuff often at work for "one off" test fixtures, as did several other engineers.

I don't know much about RF design (learning more is an item on a long list of things I want to do), but obviously part of the problem with doing it is the exponential cost of test equipment for it.

At least here in the US, the offshoring of almost all RF manufacturing and design has dumped lots of surplus test equipment on the market cheap. I have been getting HP Rf signal generators that sold new for over $20K for under $500 bucks. Most need repair, but I did 10 years in the cal lab at Motorola before becoming an engineer, so I can fix stuff.
 

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The 73 Road Runner had a rather anemic 318.......that's all his insurance company would let him have since he previously had a 71 Charger with a 440 for a total of 7 weeks before wrapping it around a power line pole sideways.

Note the 3 phase power supply schematic hanging from the top of the Gates HFL-3000. My task was to make it run from 240 volt single phase power without blacking out the warehouse complex.
 
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TheGimp said:
I disagree on the difficulty.
I'm not certain exactly what you are disagreeing with. Are you suggesting that people who don't know what they are doing can successfully build transmitters simply by following an ARRL handbook design? Such people would quickly find that handbook designs are not intended for them, but for those with the necessary skills and test equipment to debug their own build. This is not a criticism of ARRL designs, but RF is not like audio. Homebrew amateur radio is not the same as kit building.
 
It is possible to build a working transmitter by following one of the construction articles in the old ham radio magazines, ARRL handbooks, and even old general electronics magazines EXACTLY as published. That is hard to do today since many of the old parts no longer exist.

The popularity of Japanese radios, the demise of Heathkit and other ham kit makers, and the difficulty in DIY building radio equipment led to a long dark age from about 1980 to about 2010. The ranks of amateur radio operators dwindled during that era, at least in the USA.

That has changed in recent times. The popularity of low cost simple SDR radios, and several internet published designs, particularly the Soft Rock and its variations have led a comeback in DIY radio equipment. Most of this however is aimed at the HF frequency bands (1.6 to 30 Mhz) and low power levels (under 20 watts). There is a 100 watt PA board and parts kit for the Soft Rock though. A few years ago it was stated that there are now more licensed hams in the USA that ever.

Can the average DIYer design and build his own ham set and verify that it meets legal requirements? I doubt it. Can the average audiophile design and build his own HiFi system and verify that it meets the design goals? I doubt that as well, but I will state that the probability of success is higher.
 

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> OP is in Australia. ... I don't know how well such things are enforced.

They find, seize, and fine. Reported seizures as small as 40 Watts.

"While ACMA inspectors are travelling around, they normally have a spectrum analyser running in the vehicle."

"Penalties for these offences can result in fines of up to $270,000 or up to two years imprisonment."

More unlicensed broadcasting stations shut down | ACMA
FM radio pirate prosecuted | ACMA
Illegal transmissions from Christmas Island stopped | ACMA
More unlicensed broadcasting stations shut down | ACMA

https://en.wikipedia.org/wiki/Pirate_radio_in_Australia

2011: August–November. 105.7 MHz ... closed by the Australian Communications and Media Authority consequently having equipment seized.
2011: 25 September-5 October. ... Australian Communications and Media Authority reported that it shut down an unlicensed AM radio station operating on 1485 kHz
2016: February 29. Dan Morris's West Wollongong home was raided by the ACMA... fined Morris a total of $3,000 and ordered the transmitter be forfeited.
 
DIY transmitters are perfectly legal if you stay within power limits. It's not real hard to build a simple 100mw (input power to final RF amplifier, not radiated) AM broadcast band transmitter. Lots of those old phono transmitters of yesteryears used very simple designs to do just that to send it to your radios around the house.
Also there are leaky cable transmitters you can build that the FCC allows up to 50 watts of power into the power lines, which collages used back in the day without license requirements. Just had to connect the radios to the same power in the building to pick it up, or near by.

With FM broadcast band you are restricted to around 10mw of power, but it's more strict because it's field strength regulation, not necessarily power output since high gain antennas can be made for the band, but general rule is around 5-10mw power and you're safe from the FCC.

Most of these simple micro transmitters are incredibly easy to build really, just a simple tuned oscillator and modulator stage. Can be made far more complex with PLL oscillators, digital tuning readouts, audio limiting and pre-emphasis filtering, stereo multiplexing, etc.. to get broadcast quality sound.

If you want to cover a small trailer park or drive through theater you can easily do it with either AM or FM this way. With AM you can get far more distance, up to 1/4 mile legally usually. FM it's possible too if the listener uses a car stereo or sensitive house tuner.

Not condoning illegal activity but really anything transistorized with only a powered oscillator stage that is modulated is likely to fall within the Part 15 FCC rules and will be legal. Even a bit more power than field strength measurements will probably fall unnoticed.
Pirate radio is a whole other ballpark and suited to a much different forum obviously, and most pirates these days stick to shortwave on the 6850-6955kHz band. FM pirates are a dime a dozen in large towns and in some places like Florida can get cops at your door, not just the FCC.
 
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Tubelab_com said:
It is possible to build a working transmitter by following one of the construction articles in the old ham radio magazines, ARRL handbooks, and even old general electronics magazines EXACTLY as published.
Not quite true. Practical Wireless was famous in the UK for publishing designs which a certain author had not properly debugged. I'm sure the ARRL does better than that, but unless many prototypes have been built and component tolerance carefully tracked you can never be sure that an exact copy will work first time.