[Central-Electronics] "Huffed and Puffed" my VFO with X-Lock 2.0

[Jim Candela]

>----- Original Message ----
>From: Bill Kirkland <kirklandb at sympatico.ca>
>Any measurements on the phase noise/spurious of the conditioned VFO
>e.g. before and after ?

Reply by Jim, WD5JKO:

Bill,  I did have some jitter and 120 hz FM with my first try using the BC-458 VFO with a simple homemade H&P circuit. To keep from generating FM, the H&P power needed to be pure DC and not shared with something else. That circuit would H&P within a +/- 64 HZ window making it barely usable.

The Cumbria X-Lock 2.0 has dual power supplies and opto-coupled control voltage from the digital to the analog control stage. The R-C time constant is pretty long and hence the control loop bandwidth is very low. I've set my receiver at say a 20HZ beat note, and my guess is that the note might change no more than 1-2 HZ / second, and is often not noticeable. My Tx usually is within 5 hz or better from where I set it. 

The trick with these designs is to have more  frequency control range than what is needed. For example, my Band Hopper VFO in stock form drifts ~ 800 HZ from 1 minute on to 1 hour on. It drifts a whole lot more in that first minute from the initial oscillation point. My varactor control range is about 0-2400 HZ at 0-7 volts. It is possible to run out of tuning range if the drift exceeds the available frequency shift. Cumbria recommends a 20KC tuning range from varactor control. In my case I need to cycle power once after maybe 3 -5 minutes from a cold start (this discharges the analog control voltage), and from that point I'm locked really well indefinitely.

This upgrade is a huge boost to me whenever I want to run vintage SSB. No more, "hey OM your drifting out of the band"!! The threshold these days for that comment is about 150 hz drift. ;-)

Regards,
Jim
WD5JKO