[sdiy] voltage-controlled AM radio tuning

[Mark Rivera]

with a fast enough motor, or maybe a couple of gears and a servo, you
could approximate sample-and-hold :)

how nice that would be driven by a sequencer...


On Sat, Mar 14, 2009 at 1:21 AM, Paul Perry <pfperry at melbpc.org.au> wrote:
> 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
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