[sdiy] High frequency VCO designs

[Neil Johnson]

Hi Tom,

> What contemporary VCO designs are there that can cope with frequencies
> between 20-40MHz?

Depends on what range of control you want.

> There were several synth designs based on top-octave-dividers that used a
> high frequency VCO to clock the divider (PolyMoog, for one example).

The Jen SX1000 uses a 74LS221 running at about 2MHz to provide the
master clock, and is wobbled around a bit by the LFO for vibrato.

> 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?

Some versions of the 4046 PLL chip can run the VCO up to 10-15MHz.
If you only want a narrow tuning range then maybe a varactor diode to
pull a crystal in a Pierce oscillator?
Something like the Radio Communications Handbook (UK) or ARRL Handbook
(US) will have some VCO ideas.

Neil
--
http://www.njohnson.co.uk