On 02/24/16 15:20, Big Bad Bob so wittily quipped:
I was thinking you could build one with some kind of balanced modulator,
with a detector on the output creating negative feedback to limit
distortion. you'd bias the modulator at 50% for zero signal level, and
then it should give you up to 100% with minimal THD. But that
transmitter also has a 5:1 compressor and other things you really need
for an AM transmitter. So yeah, probably can't build one cheap enough
(and have it be 'legal').
etc.
https://richmondradio.wordpress.com/...m-transmitter/
"The modulation is accomplished an older but quite capable (and still
available) MC 1496 Balanced Modulator/Demodulator IC. For AM operation
we don’t want a balanced condition so the chip is biased such that the
carrier is not nulled out."
a cheap method of carrier injection would be to DC bias the balanced
modulator such that the zero-AC-signal output power is the 'rated' power
(in this case, 100mW for FCC legal). Looks like this guy is doing "that".
I recall balanced modulators (and carrier injectors) being used in U.S.
Navy comms gear designed in the 1950's (with freq. synth, crystal ovens,
and lots and lots of tubes). It gave you SSB, supressed carrier AM, and
regular AM with the same unit.