I got a little tired of Si5351 and decided to build an analog CW transceiver. It's almost done and works pretty well. However, I discovered one problem. When I reach the VFO control with my hand the frequency shifts a little, about 100 Hz or so. It's not a big deal, but a little annoying. When the frequency is higher, ~5.070 MHz (the capacitance is less) it gets worse. I wonder if it's curable.
Here is the schematic:
And here is how it's physically implemented:
The enclosure is made of thick aluminum and as you can see I did my best to shield the VFO properly, but it didn't save me.
I never encountered such an issue before and I don't recall that it was well described in the literature. For instance, I don't know for sure if the choice of the component values matters, and if so, what are best practices worth considering. Is there anything I can do in my next rig to avoid this problem? Or is it simply the price to pay for using a capacitance-controlled VFO, instead of, say, varicap-controlled VCO?