Crystal Osc. + Class AB Linear Amp Transmitter

[choppergirl]

I thought I'd share, here are some pictures of my first attempt at building a minimalist (as few parts as possible) short wave transmitter, which has stalled from lack of parts and kind of, from interest.

Most transmitter schematics I find are far too complicated and involve too many parts, so I wanted to try see if I could build something of (hopefully) 5-10 watts with as few parts as possible:




Here is a link to my thread about it, with links to a lot more pictures:

--> www.wahlberg.cc/sm0vpo/forum/forum_posts.asp?TID=711&PN=1&SID=26112482f9face45f33c726dbzc2141220,751087963 <--

The values for the components are listed on this page under "Components for Class-AB amplfiier"... mainly I never got around to ordering the CB power transistors from China/Ebay... plus his custom little home made ferrite bead coils throw in another complication...
www.sm0vpo.com:800/tx/rf_pa_cct_00.htm

Mostly I was scavenging parts out of old TVs thrown away in the woods and anything junk I could find. I'll add that I'm not an amateur RF engineer, but come from a computer hacking / python programmer / game design background, so this was kind of just a new hobby to try.

I lost interest this project or got distracted by modding my DX-160 with a lot of cool backlights, mood lights, and LEDs controlled by buttons on the left side, which was a little involved project in itself, and listening to the DX-160. Also I was playing around with an AA5 vacuum tube radio I had trying to squeeze as much MW performance out of it as I could.

I think what killed the interest in the project for me was how complicated and involved these builds are, for even a low powered transmitter... plus you run the risk of pissing off the Feds (I don't much care about that really, I was going to go mobile with my broadcasts)...

...and mostly, propagating a radio signal reliably with a low powered transmitter with the flakiness of mother nature and the ionosphere through a bunch of static seemed hopeless. I have yet to pick up a single pirate radio stations in the 6.9-7.0mghz range with my long wire.

Maybe I'm spoiled by the web, where any digital data you send out is received 100% without error, without static, on the farthest side of the globe even, to a larger audience.

[Kage]

Awesome thread!
Welcome to the forums.

Sometimes minimalist works best and I can see where a simple transmitter like that would probably work just fine for a few watts of power.
The transistors would need heatsinks for anything over a watt of power.

As for listening to shortwave pirates your best time is in the evening hours right after the sun goes down. Listen to 6925kHz. That's where the majority of pirate activity is. A lot of it is in upper single side band (USB) but occasionally they will use AM.
Weekends are usually the hottest time to pick them up.

[choppergirl]

Well, I tune 6.925 all the time... as well as searching anywhere between 6.900 and 7.000... as I listen to the hams on 40 meters from 7.1 to about 7.250. My own station I want to locate eventually some day at 6.970 by adding an nicer sine way simple oscillator circuit and plugging in a custom crystal of that frequency (assuming I could special order one from somewhere).

I suspect I'm not getting any because perhaps most pirates using low power transmitters out of New York, or even further... Europe. And also, I've read, they are mostly active during Holiday Seasons. I get plenty of stations through my DX-390, but so far anything pirate has been elusive (unless I stumbled over a Spanish one, which I wouldn't know it anyway).

~

Someone recommended for my linear amp transistors: "Pretty much any CB radio final output transistor would work, the 2SC 1066, 1306, 1307, 1969 and 2078 should all work quite well in that circuit and the 1307/1969 are very nice devices, in push-pull you can easily get some 25W of RF from them."

What are the differences between these different types. They are all generally about the same on ebay. I've read though you have to be careful buying them because there are a bunch of counterfeit/fakes out there.

~

Also, does anybody see any serious flaw in my design (other than its straightforward crude) that would keep it from working? Just plugging up the crystal square wave oscillator to my audio transformer and dumping it on an antenna, I get a range of about 50-200 yards. The rest is just dumping the oscillator output into a linear amp, then a simple filter, then out to an antenna of the right calculated length for my frequency.

I may go ahead and build it, but after thinking and reading up more about it, it seems the best pirate transmitter is just to buy a surplus commericial HAM transmitter and then operate it just outside the HAM bands (so as not to piss off the crochity old hams that would rat you out in a New York minute for encroaching on their sacred RF turf).

[Deleted]

Sweet!

I'm going to teach that "breadboard" method to youngin's ;D

Welcome to the forums

Cheers!

[choppergirl]

I originally saw a Youtube video of a guy from India using thumbtacks this way for point to point soldering... and I thought, hey, that's clever, and way cheaper than Ugly style or Manhattan style... thumbtacks are dirt cheap. Why don't I take it a step further and make my circuit diagram to accomodate them, where the first step you do is just lay the diagram down and place thumbtacks everywhere you need them? Then people who wanted to duplicate my project, could just print out my circuit diagram, and then go to town with thumbtacks, parts, and their soldering iron as if it were a kit.

The next step is making pre-making soldering pads on top of the thumbtacks. It helps if you coat the entire top of the thumbtack with solder.. so it binds and you're sure you've heated up the thumbtack as well. Just like regular soldering rules, if you don't heat up the metal you are binding (the brass thumbtack) to it won't chemically bind (like a cold solder joint) and just slide off.

Make your print out like I did, where you can just put it down and use it as your guide, with all the parts in between labeled with values... and better, colors (for resistors) or pictures even (like for electrolytic caps).

The cardboard box was an experiment, I suggest you use any old piece of cut and sanded wood instead for a more permanent build. I just wanted to see if the paper would burn... the answer... no. In fact, I wiped my soldering iron off on the paper many times without even so much as browning it. Any brown you see is the flux from the soldering iron.

~

I took a look at the Junker and Chug builds... very appealing, and I like the idea of using old stereo / vcr cases. I have a ton of old 486 minitower cases.

I also like the idea of using old regulated AT power supplies, but you're limited to +5 and +12 output (you also get a -5 and -12 for bias).

My station won't be broadcasting music, so high fidelity is not so important as getting at least a little bit of juice out of my transmitter. The thing is, even the lamest HAM transmitters do about 100 watts, and some guys out there are cranking out 400 watts... it makes anything I could build putting out 1 to 10 watts seem... pathetic and pointless. Better to save up some money and buy a decrepit old HAM transmitter and repair it.

The old Collins and Drakes are suppose to have a real nice sound, but are $$$.

[Kage]

Keep in mind that 10 watts is only half the power of 100 watts, and 1 watt half of 10 watts.
So 10 watts is anything but pathetic. It's easy to cover 5 miles or more on AM with 10 watts and a properly tuned shortened antenna, or the entire US if using shortwave.

The problem with amplitude modulation is that whatever your carrier power is, your output
transistors must be able to handle 4 times that so as to be able to handle the full 100%
modulation.

So 10 watts carrier will need transistors that can at least do 40 watts on peaks.
That is where things start to get hairy with cheap CB transistors and the like since most of
them are made to only handle 16 watts total (4 watts carrier).

[choppergirl]

Ug, more complications... again, another reason to chose a HAM transmitter designed and built by the 'old masters'... that can do SSB... and +++ to your effective range by not wasting energy doubling the bandwidth. The nearest city for me is 25 miles away for me, so 10 miles is nothing. I'm interesting in going *long* in the afternoon off the ionosphere. MW local does have an appeal to me though, to compete against these evil local conservative talk show radio hosts.

~

You should refine your Chug transmitter to bum down the parts count on it (like Woz did on the Apple 1), and offer it on ebay as a kit. Maybe partner with adafruit or someone who likes to throw together parts in a ziplock baggie and call it a kit. You'd have to engineer out any custom made parts... well you wouldn't have to, but people really really really hate winding custom coils.

Since grenade transmiters aren't available to anybody... and there really is no good defacto homebrew single AM/SW pirate transmitter out there that hit it big... if you think you've hit upon something that is the cat's meow, you should polish it up to be a de facto go to home made transmitter for the wanna be AM pirate out there. Might be a shot of juice in the arm for the scene. I think the scene is dead, but supposedly the sun spot cycle is suppose to swing back to favor radio soon, and there might be a big resurgence in the hobby on the near horizon if that's the case.

There was one simple and crude 7 watt transmitter I was looking at by Kyle Drake that looked not too hard to build where he modulated the final output with a very heavy audio input signal from an audio amp... but he was still refining it when he posted the schematics. I have an audio amp so that part I wouldn't have to build:

docs.google.com/viewer?a=v&q=cache:yFa71FX7u0EJ:www.profesaulosuna.com/data/files/TELECOMUNICACIONES/AM/AM%25207%2520WATTS/7.doc+&hl=en&gl=us&pid=bl&srcid=ADGEESiDZ6mtav8AA8qBAgyV6etUTh-jerllhYQqBoDrGhIZYvjRCM1Idcm8ZlxuAyLH8EyQlxVxvuuTg4ZAFh5ly_9FgdFRaQZIM9AjNLrYIUnZjh6En7h-L43rXGV7Sx2otDThVdMP&sig=AHIEtbQxf6A8B5M2F4nh7FkCwLtPbRz8fw

I also found this webpage very informative:

Transmitter Building Blocks
hlrinternational.tripod.com/id5.html

~

Oh yeah, and as far as using wood with nails or thumbtacks in it for a PCBoard, balsa or some sort of soft pine (much cheaper) would be the way to go. Cut it to fit your schematic, outer the edges to be rounded, sand it, stain it, then glue on your schematic with spray on glue. The downside being of course, you don't have a big sheet of copper acting as a ground plane which probably helps cut down on RF noise and other spurious and nefarious things going on inside your circuit.

[choppergirl]

Now, I do have a Belkin Tunecast II I modded to bypass a limiting resistor going to the antenna and extend its range a tiny bit... which is now about a football fields length. It tunes from 88mghz to 108mghz digitally which is nice.

If I were to shoot its antenna output into the 5-10 waqtt linear amp used above with the CB transistors, or with a HAM transmitter linear amp, I'd have one hella FM transmitter, correct? Because FM carries so much further than AM locally, watt for watt.

I'd also have the FCC all over my ass in a heartbeat I imagine.

[Kage]

There is no way you are going to get that belkin transmitter to work with CB transistors simply because almost all of them have an
upper amplifying limit of around 30-50MHz before they have unity gain (no amplification).

Besides that you'd need to buffer the signal many times over before you will even get the driving power needed to drive those kind
of transistors which is usually around a few hundred milliwatts. The Belkin being a part 15 legal transmitter probably puts out much
less than 10 milliwatts of power.

Finally.. you wouldn't want to even try that if it could work because those cheap transmitters put out lots of harmonics/spurs and can
cause interference to unintended frequencies, not to mention the audio quality they put out
is .. well .... only good enough for it's original purpose and not for quality broadcasting.

You can get one of those cheap chinese transmitters off of amazon or ebay for under a hundred bucks that can do 5 or 10 watts
which with a good antenna up 30 to 50 feet could cover tens of miles but once again their
audio quality is pretty bad compared to good quality exciters that licensed radio stations use.

Don't let this sound discouraging though. We all start small and work our way up with better equipment, experience, and
knowledge in this hobby.

[choppergirl]

Yeah, I looked at those cheap ebay Chinese transmitters a while ago (Hollys, clones, etc I found a page comparing them all) and read a bunch of negative reviews on them.. that, and they are still way out of my price range.

My best bet probably is to score an unused Ham transmitter (like a Heathkit) somewhere from a Ham that has a big collection of that junk. Trade them some computer equipment or something (of which I have barn fulls). Hams hold onto this junk like it was some kind of priceless jewels... until they die anyway, and then a whole bunch of it comes on ebay at one time when their crackhead relatives liquidate it all as part of an estate.

If you listen to the HAMS (every now and then they talk tech which appeals to me), you realize, most of them are getting way up in years... they're all retired, their vision is going, and they need to hire people to climb up whenever any antenna needs put back up... and they sign off to 'take their meds'. That means give it 5 to 15 more years, and you'll be seeing a lot more old transmitters coming on the market as they clean out their shack of surplus (or just die).

I learned a lot by reading "Crystal Sets to Sideband" ( www.wa0itp.com/crystalsetsssb.html ) but a lot about how circuits work and the various ways components can be used or behave... is just mystery to me.

All I know... Capacitors block DC but let AC signals thorough... transistors let you control a big current by using a smaller current across a gate... (or you can use them like a logic gate)... chokes block RF signals.. transformers step up or step down voltage... diodes are one way and crystals vibrate to their frequencies... and resistors resist the flow of current. But much beyond that and it starts getting greek to me.

I'm still trying to get my head around why an antenna has to match a transmitter for impedance with an antenna tuner, or what ferrite cores do different than an air core ( en.wikipedia.org/wiki/Magnetic_core ).

Anyway, unless I can get something hacked together that broadcasts further than a football field in length (besides the store bought handheld FMRS radios I have) I'll probably lose interest. Radio just seemed kind of retro cool to me, but it also seems rather flakey and unreliable, compared to say, a global WAN, and the world wide web.

For example, I'm exchanging data, images, and a discussion with you error and static free through your forum running on your webserver, not via a transmitter and radio either of us have or built. So why bother with radio?

Or when I listen to HAMs and think, hey, if you guys can't copy each other, why don't you just pick up your cell phones and dial the other person. Seriously ;-)

These radios are a curiousity, but unless you have a lot more power (lighten up, FCC) and are transmitting digitally packet radio with error correction, AND mother nature (or the sun or thunderstorms) isn't PMSing 3 times a day, then you're never going to even be in the same ballpark of the crystal clarity that information is distributed across the internet.

Radio.. old arcane wizardry of a lost elmer generation...

[Kage]

Nov 8, 2012 22:32:31 GMT -6 choppergirl said:

For example, I'm exchanging data, images, and a discussion with you error and static free through your forum running on your webserver, not via a transmitter and radio either of us have or built. So why bother with radio?

Because it's fun?

Everybody has a radio in their car and probably a dozen radios laying around their house.
Not everyone has internet access in their cars or take the time to try and listen to broadcasts
over their computer or phone.

Also the medium itself (AM/FM) serves a community much easier then other means.
You may have a few hundred listeners if broadcasting online but how many of those people are local?
With radio broadcasting you can reach your town and surrounding towns directly, no need for a connection.
The audio quality that can be had with FM broadcast can rival that of almost all internet
broadcasts unless you're paying some serious money to run your own server and high
enough speed connection to allow those hundred some people to connect and listen to
your stream.
Pirate radio only cost money to run the transmitter which is almost nothing for the power
levels we run to reach our community.

Shortwave has a magic of its own but unless you ever get the opportunity to listen to other
pirates on the dial it's hard to understand the fun that can be had with it.

As far as the amateur operators go, you may want to find out where the nearest "hamfest" is
in your area where they all get together to sell and swap equipment.
It's very easy to get some old gear that can easily be converted for shortwave or even medium wave use.
With enough social engineering you could probably swap an older computer or buy a
transmitter for next to nothing from them. Just don't let them know you're using it for pirate use lol.

[RFBurns]

Those CZH/HILLY/FMUSER/Clone units aren't all that bad...if you know what to do to them once you get them.

Their main problem is the use of SMD chip caps in the high power sections..ie IPA and PA sections. These SMD chip caps are no where near the ratings for power dissipation that flows through those circuits, thus the SMD chip caps shift value within a very short time and throw off the factory pre-set tuning.

Had they incorporated variable caps, it would be a different story.

They are simple to modify to output a very clean signal, most of which takes place at the 2nd or 3rd IPA stage, where most of those units are simply coupling from the IC (BH1415) to raise the signal level, but with no tuning stages or bandpass filtering in between, thus by the time the signal reaches that final, that final is amplifying both the signal you want, plus the crap generated by that IC chip.

I took a CZH 20A unit and applied Ramsey's bandpass filter out of a FM-100 unit, and that not only cleaned up the signal from spur and harmonic, it actually helped the first stage amplifier circuit focus it's gain on the signal instead of being scattered by passing unwanted signals.

All that is needed to clean those things up are 4 parts. Two 5-30pf variable caps, and two coils wound 5 turns on a 1/4 inch drill. Install in place of the crappy tuning stages and there ya go.

Plus those overseas units from China are factory designed for wide band use, which is ok, but given the use of low power SMD chip caps and no tuning in between stages, and that they are built for "no-tune" operation, that all adds up to their down sides right out of the box.

Your AM transmitter design is a great start. However your going to be limited with that crystal oscillator block. I would make the following changes:

1. Use THIS, a PLL Oscillator board that outputs the frequency you wish to operate on.

2. High level modulation. Change the final circuit to accept high level modulation instead of modulating at the front end. Less distortion, better linearity and fidelity. And you won't have to worry about building a proper bias circuit to set the final stage up properly as needed with low level modulation (front end/balanced modulator approach).

3. Always remember, anything worth spending time on is going to take spending time at it.

4. Approach ham's with caution. Mention anything about license free radio and your an instant criminal, even if your just discussing it. They are a strange bunch, probably why I quit messing with ham radio and let the license expire. True freedom radio is more fun IMO!

The "thumbtack" layout is actually not new. There was a run of kits prior to those "spring" all in one kits. They used the very same approach, a sheet of cardboard with the circuit printed on it, thumbtack points and the "Manhattan Style" build.

Peace!