Is There Anybody In There?
On 12/06/15 05:56, Patrick Turner so wittily quipped:
I dunno how they'd do AM now, lots and lots and lots of utterly incomprehensible didgets & bizibots I guess.
here's what _I_ would do, if it were solid state:
a) use a ring modulator with VERY heavy negative feedback
- or -
b) use a relatively linear MOSFET biased to its most linear zone with a
tube-like modulation circuit, i.e. source-feed from osc for carrier,
gate modulation.
- or -
c) use a "digital exciter" circuit. probably a ZILLION ways to make
THAT work. I'd give PWM a try. for 455khz IF modulator, you'd need
455Mhz with divide-by-1024 and 12-bit accuracy. THEN, modulate the
455Mhz with 455khz digital signal, with amplitude calculated based on
digital sampling of the input. Input is at 0.5V, output swing is +/-
256. Input is at 1V, output swing is +/- 512 [max modulation]. Anyway,
that might be kind of interesting.
- and -
You'd use an IF freq. for the modulator, maybe 455khz like AM receivers,
then drive this into a freq. synthesis converter, similar to old-style
"crystal oven" freq. synth transmitters the Navy used back in the day.
it should work for just about the entire range, and you should be able
to use tuned SSB mechanical filters on the transmitter IF, with an "add
carrier" level adjust.
but yeah, BEST way to do AM modulation (In My Bombastic Opinion) is with
an IF carrier, so you can do SSB and 'carrier injection' and whatnot via
off-the-shelf mechanical filters and THEN drive the transmitter through
a freq. synth. thingy. Super-accurate, good quality SSB, built-in
ACCURATE carrier generation for SSB reception, and so forth.
[that worked really nice with TUBES back in the day, it's how the Navy
transmitters (that I studied for ET 'A' school) worked, though they used
solid state switching diodes to generate harmonics for synthesis]
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