More on the "Huff and Puff" stabiliser

It has been three months since I switched on the soldering iron! Blame it on work. At least the Christmas holiday has given me the chance to pick up again on various amateur radio activities.

One of these is further testing of the Ugly VFO with the "Huff and Puff" stabiliser module. After exchanging emails with Ron Taylor G4GXO from Cumbria Designs, it seemed that the 68pF coupling capacitor between the stabiliser and the oscillator might be too big. Ron suggested that a 15 - 20kHz frequency change (for a 12V swing on the varactor control voltage) would be right. I measured my circuit and found I had 50kHz range. Reducing the 68pF capacitor to 10pF has brought this down to 15kHz.

The oscillator has been long-term stable in tests yesterday and today. It slowly hunts around the desired frequency, but has stayed on frequency for several hours at a time.

I read somewhere (the X-Lock manual or the emails from Ron, not sure which) that experimenting with the value of a time constant resistor could improve performance. I'll try that next.