HFU HF Underground
Technical Topics => The RF Workbench => Topic started by: digitalmod on December 13, 2017, 0136 UTC
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Those of you who are engineers in the black arts, here is a little brain fart I had.
Get Streachy's little class E rig. He says ten watts (that's the fuse).
Now, go yeah and get a 300 watt class E design and the transmitting caps etc, you will need. If you build a 50 volt dc supply supper, but saves time pick one up. Many commercially out there.
Realize the Pirate trade can just as easily go to basics and use ROCKS (crystals)
The Little Starter Transmitter can be made to work about anywhere. Now take a peak at the low pass filter. Yes, but if you use this as an exciter, no way you need worry about harmonics in exciter. You filter those in the final class E 300 watt amp .
Modulator? Well, if you can find a 200 watt class D amp. Yes these amps for audio on Ebay else where for LESS than 100 USD.
Now the creative part, bridge the stereo channels. 100 watts per channel becomes 200 watts of audio, enough to even over modulate a 300 watt class E. But, you need an audio quality transformer. Or use some other creative way to series modulate the class E stage.
Output matching Pi or yes even a RF transformer to 50 ohms nominal.
The FETS at between 300-500 watts present a damn close output impedance at 50 volts of 8-4 ohms. Idea for high power audio amps and this you will recall is speaker level impedance.
Upshot.. transformer turns ratio damn close to unity, i.e. 1 to1
So that's my naughty thought. 8)
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Basically what this guy did...
http://amfone.net/Amforum/index.php?action=dlattach;topic=30798.0;attach=31360 (http://amfone.net/Amforum/index.php?action=dlattach;topic=30798.0;attach=31360)
Class D full bridge RF amp fed by a torroidal power transformer and a high power audio amp.
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The 48VDC power supplies may not be too hard to get, since (As mentioned earlier.), commercially many STL and other microwave station links run -48VDC. There's also a lot of +36VDC from the Railway industry, so they can be had, but if ya see these power supplies out there for dirt cheap, there usually a reason for it. I see that Radio Systems uses 48VDC for their 10W AM TX, http://www.radiosystems.com/lowpower.html Just that $3,500.00 price tag turns me off.
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Digikey, Mouser, Jameco all have 48V supplies from 25-2.5KW. My current prototype runs on 3 48V supplies turned up to 55V and wired in series to get 165VDC for the modulator.
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::) There seem to be designs out there. YES! There are hammer radio guys who elite theirs on 75 meters. In some ways such transmitters are easier to design than the ole mod transformer high level jobs.
But talk about anybody who has seen this as a potential for a little business (under ground). If they are there??
Years ago I almost bought a transistor 300 watt linear amp. The dude did have the units even built. Big issue here. If its a KIT and you are not a radio jolly rodger.. just want ham it.. well.. that legal. Built forget it dude. FCC demands type acceptance for virtually everything from CB to FM broadcast. I have a 300 watt, FM amp drives with 1 watt, BUt..... its not type accepted so using it in licensed broadcast service, just isn't possible. Tried to sell it quite a few times and of course the licensed stations can't use it so its value?? Zilch?
Now, a basic 250 watts class E for shortwave should be a piece of cake! Dude its NOT rocket science!!
But, nobody has surfaced, maybe for good reason, who supplies these things. Could Old Streachy do it someday? I have not a clue. Its up to I suppose basic economics.. can I do this legally? Well, yes you can.. its like guns.. you sell them, but its in how they are used. :P
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Yes, it's done already....
However it's no 'Business' no matter how much 'WE' like it.
If I sold 20 high power units I'd be VERY 'Surprised'.
BTW I have a full time 'Career' as an RF TEST contractor and fortunately I can command a decent rate as there's no one with the required skills anymore.
This helps to fund my hobby and passion for building these things but you have to be dreaming if you thing it would earn more than a $2K/pa.
It wont, ever!
However I will keep on building and designing stuff, just wish I had more time!
Str.