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Old May 23rd 06, 01:02 AM posted to rec.radio.cb
Dr.Death
 
Posts: n/a
Default SkyWave 2879AB Amplifier

"Jan Panteltje" wrote in message
...
On a sunny day (22 May 2006 07:47:53 -0700) it happened "Telstar
Electronics"
wrote in
.com:

Jan,

Sure you can run class D at 27MHz... the problem is distortion. Class D
is very efficient but is really only meant for digital signals.

www.telstar-electronics.com


Hi, you know class D audio amps exist I suppose?
There are even class D power amp chips for audio.
These use PWM (pulse width modulation).
You can make any output waveform with PWM (as long as the switching
frequency
is much higher then the output frequency).

This links shows some basics for a modulator (driving class D for
example):
http://www.netway.com/~stevec/ham/pd...lid_state.html

I can also think of a 'digital' solution, say you have 8 RF amps,
1W, 2W, 4W, 8W, 16W, 32W, 64W, and 128W,
now simply switching these on with an 8 bit digital audio signal (one on
each
bit) and summing the RF output together, will give you a 255W AM modulated
transmitter with less then 1/255 (0.4 percent) distortion (have not
tried)?
Since these RF amps can be class C (no need for A, AB, B, any linear!!)
you
should get good efficiency.
The stages are only 'on' or 'off'.

So, maybe someone could combine some :-)
Nice for experiments....
hehe



Class D audio amps are only designed for low frequency as they would sound
like crap for the higher freqs.