I've been familiar with the Polar Explorer QEX article since it was first published.
One aspect of it was it takes us back to the days to separate transmitter and
receiver like my old Hallicrafters HT-37 and matching receiver. One reason
that became unpopular is it did not reuse hardware and later transceivers did
reducing bulk and space. For high power that's less an issue for low power
system level efficiency (overall DC to RF) takes precedence and just feeding
the cpu/display for a 5W tends up unbalance the effort as its more than 20%
of the overhead.
As time progresses and I get back on schedule for projects I will revisit
For certain the Q6 amplitude control circuit needs to have a distinct low pass
filter to keep the PWM products out of the generated signal with a high enough
pass (maybe 4-5khz) for audio rate changes. Doing that adds some amount of
phase delay. The collective error there impact intelligibility more than bandwidth.
Class D and E however has made great inroads in the production of high
power and high quality AM signals.