[sdiy] voltage-controlled AM radio tuning

[Roy J. Tellason]

On Saturday 14 March 2009 04:25:20 pm Cary Roberts wrote:
> >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.
>
> That's actually a pretty good idea.  Servos are PWM controlled.  50hz with
> a pulse width of .5ms to 2.5ms (1% to 5%) for most servos.  This would be
> pretty easy to implement with a 555 timer and comparator.

When our family took a trip to Germany in 1960,  my mother bought a rather 
large radio,  brand name "Saba",  to have sent back to the US.  That had a 
very similar function,  though it only worked on the FM band ("UK").  That 
was implemented with vacuum tubes!  They used that to compensate for 
frequency drift,  rather than the later AFC arrangements.

Nothing new here!


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