On Nov 25, 8:10*pm, lw1ecp wrote:
Hi!. I need to cover the HF and VHF ranges with as few VCOs as
possible. Think of this as the varactor version of the old general
purpose RF bench generators or grid-dip-meters. I know the penalties:
high phase noise, high drift, high harmonic content. I don't care,
this won't be made into a high dynamic range receiver.
What I do need is a reliable means to keep the peak-to-peak RF voltage
across the varactors (varicaps) below 1 or 0.5Vp-p.

Look at the Elecraft K2's VCO. A single VCO covers all the HF bands
(some with up and others with downconversion), with many narrow ranges
all cleverly switched using small relays to move the varactors/fixed
capacitors in and out. I can't promise that this is exactly what you
want but there's much to be learned by studying it if you want to
build wide-range VCO's with commodity parts.

The Elecraft K2 VCO also uses a clever scheme to do AGC such that the
VCO output remains constant through its wide range, this probably also
keeps the RF voltage across the varicap in check.

There's a lot of cleverness in the K2. Schematics are online, www.elecraft.com.

Tim N3QE