[sdiy] High frequency VCO designs

[Roman Sowa]

Any kind of RF oscillator with varicap or saturated choke as voltage 
control. Look for short wave radio schematics, there should be lots of 
that. Make the osc tunable range at reasonable 200-250MHz. Then down 
convert it with 200MHz fixed oscillator and as a product you get VC 
controlled 0-50MHz output. Now feed that to PLL to synchronize with 
typical audio VCO running at 0-40kHz.
A bit long feedback path: RF -> downconverter -> filter -> divider -> 
PLL -> filter -> RF control, so it may be tricky to get it locking fast 
over entire 50MHz range, but it's worth trying.

I think it was discussed not so long ago...

Roman


W dniu 2014-09-22 23:01, Tom Wiltshire pisze:
> Hi All,
>
> What contemporary VCO designs are there that can cope with frequencies between 20-40MHz?
>
> There were several synth designs based on top-octave-dividers that used a high frequency VCO to clock the divider (PolyMoog, for one example). It occurred to me (and I'm not the first) that whilst you can't copy aTOG chip in a PIC, you can adequately copy a single output of a clock chip and it's associated divider. This is closer to the older 12-separate-oscillators-plus-dividers scheme. But that's fine, better even. The important thing is to get some voltage control in there by using a VCO for the uP clock.
>
> So, VC-clocks for a PIC? Any ideas?
>
> Thanks,
> Tom
>
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