EMRFD Message Archive 14906

Message Date From Subject
14906 2018-07-03 04:10:34 Andrea Baldoni Applying varactor tuning to a Vackar - some experiments

I made some experiments about how to reduce amplitude of oscillations and
I would like to receive opinions.

I'm still referring to the circuit in Fig. 4.14 B, page 4.9.

Applying "automatic" negative bias to JFET gate, adding a 1N4148 to GND,
works exactly like in the other oscillator topologies.

This reduces amplitude in this node to about 1.4Vpp; in my case in the tank,
voltage is still too much. Of course peak-peak amplitude stabilize to (slightly
more than, because there is the negative bias) twice diode Vf so with different
diodes I can reduce more, to some extent. Are different kinds
of diodes (like Schottky) better or worse? Schottky should have lower
Being "automatic", the circuit is stable. I tried to push it a little too
far by negatively biasing the diode and amplitude started to be unstable.

I also tried to clamp oscillations directly with a diode in parallel to the
inductor, with or without a resistor in series to it. It works, clamp cleanly
to twice Vf (without resistor), amplitude perfectly stable, but I suspect that
this will introduce more distortion even if the limiting actually should be
cycle to cycle and thus not too hard.