Hi all!
I got very board recently and drew out this circuit which I've been using for decades.
It's much simpler than it looks. The main circuit is U2 Q1, Q2 and Q3.
All the following are just embellishments:
- U1 is tone control (mostly to increase treble modulation)
- Q4 is a generates a low-distortion 400 Hz sine wave to help find on the transmission and adjust antenna tuning for best signal
- U3/Q5 indicate over-modulation
- Q6 drives a modulation Vu meter
It's appropriate now that I investigated a modern programmable and much cheaper substitute for the crystal oscillator.
Medium wave is going to get louder with interference, and quieter with stations. I think it's time to think ahead...
Season's greetings,
Ian