In article , James Fenech
writes
Hi Paul,

I'm currently experimenting with VCO circuits (had an earlier thread about
varactors). My current prototype uses a MPF5179, a pair of BB909 tuning
diodes and a home made inductor. The inductor is about 4 turns on 0.25"
centre (air cored), spread out to about 0.4" in length, giving about 150nH.
This circuit operates to 350MHz and (if the tuning diode info is OK)
indicates strays of less than 1pF. This is built "dead bug" style, and is
really my first attempt at anything of this sort of high frequency.
in the early 80s I built some narrow band VCO employing a 450MHz Toko
helical resonator bandpass filter.
The trick was to get the phase including amplifier and a varicap phase
shifter to zero.
I recall a -125db /rootHZ at 10kHz with a bfr bipolar.
Never got anything better though was narrow band.


--
ddwyer