[sdiy] voltage-controlled AM radio tuning

[Paul Perry]

If I had to make a voltage tuned AM radio, I'd use a different approach: I'd 
replace the local oscillator with a RF VCO (some 4046's will go high enough, 
I think.)

With AM band 550KHz to 1600KHz, the local oscillator is (assuming IF of 45 
KHz) 1000KHz to 2055 KHz.
You would need to make the RF front end unselective - easiest way would be 
to make a wide band fet RF amp (or use a MINICIRCUITS amp) and inject the 
amplified RF at the mixer in place of the previous tuned preamp stage.
OK, you will get some spurious btreakthrough of stuff above the audio band - 
but (depending on musical application) this may be no bad thing.

But if you are happy with a slower response, the coolest thing would be a 
voltage controlled motor doing the tuning. Using a small motor driving a pot 
and the tuning shaft, and using the pot as a position sensor for a feedback 
controlled positioning circuit, you could wannder back and foward at will 
using CV.

paul perry Melbourne Australia