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Old 27th February 2010, 10:03 PM   #1
Join Date: Jul 2007
Default Radio Amplification

I'm reasonably well experienced at this point but don't know an awful lot about radio.

Am I correct to assume I can use an amplifier I've built for speaker applications to amplify an FM source through an antenna?
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Old 27th February 2010, 10:44 PM   #2
wahab is offline wahab  Algeria
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not at all...

to amplfy an antenna signal, you ll have to build
a dedicated preamp using generaly a single transistor
as active device...
there s scores of such designs on the web...
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Old 27th February 2010, 11:23 PM   #3
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Hmm, FM source thru an antenna.

This isn't very clear. If you want to transmit, you can't.

If you want to receive then the easiest thing to use is MMIC, some of which extend down to the FM band. This would be a mini-circuits MAR 6 typically, with gain from DC-2GHz, 22dB @ 100MHz.


All depends what signal levels you're talking about, output @ 1db compression is 3dBm @0.5GHz

Last edited by wakibaki; 27th February 2010 at 11:26 PM.
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Old 28th February 2010, 01:35 PM   #4
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Default Try minicircuits

Minicircuits makes what is effectively RF operational amplifiers. These are very easy to use and fabricate on perf board and will run on even a poor supply. For the novice just use ceramic disc caps and it will work like a champ!
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Old 28th February 2010, 09:17 PM   #5
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I intend to transmit. I realize I'll need a transmitter to feed an amp.
I have a surplus 1,000 watt RMS general purpose audio amplifier.
My intentions is to use it as a transmission amplifier through a DIY transmission antenna I've designed.
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Old 28th February 2010, 09:40 PM   #6
jaycee is offline jaycee  United Kingdom
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An audio amp is going to be useless at RF frequencies.
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Old 28th February 2010, 09:53 PM   #7
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Originally Posted by jaycee View Post
An audio amp is going to be useless at RF frequencies.
sure if I don't bother to change the filters in the preamp stage.
I'm not a beginner, just haven't worked with radio quite yet.
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Old 28th February 2010, 11:13 PM   #8
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Originally Posted by JonnySwitchblade View Post
I intend to transmit.
I doubt you'll get any help here. It's illegal for you to transmit without a license other than at extremely limited power levels in specified bands, and they'll probably delete any posts providing direct technical assistance to you.

You may be able to learn how to do this by building or adapting equipment at the component level, but most people find that by the time they have figured out how to do this that they they understand what a goddamned pain-in-the-*** it is to people around and are no longer motivated to break the law in this particular way.

If you beg, borrow or steal the equipment to do it I hope you get caught.

Which is pretty likely since it is a RADIO BROADCAST.


...and you're wasting your time with the audio amp.

Last edited by wakibaki; 28th February 2010 at 11:16 PM.
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Old 28th February 2010, 11:39 PM   #9
infinia is offline infinia  United States
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Not for FM but for AM it's possible using an audio power amp to drive a modulator. AM uses a fixed carrier whose amplitude is driven by an audio amp, its called AM modulation. Buy a ARRL handbook for diagrams.
FM uses low level audio to vary the frequency of the carrier at a rate equal to the modulation ie the audio.
like four million tons of hydrogen exploding on the sun
like the whisper of the termites building castles in the dust

Last edited by infinia; 28th February 2010 at 11:46 PM.
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Old 28th February 2010, 11:40 PM   #10
tinitus is offline tinitus  Europe
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