Hello Steve.

Do you happen to have that schematic without the black background?? That background makes it very hard to read.

Thank you.

Jim Pruitt
WA7DUY

On 3/15/2025 1:37 PM, hwstar via groups.io wrote:

Attached is the proposed circuit. It uses loose coupling to a parallel resonant tank circuit via 1pF caps and a high impedance buffer amplifier consisting of a J310 and two 2N3904 emitter followers to get back to a 50 ohm impedance for the spectrum analyzer input.

It uses the parallel resonant tank circuit concept in EMRFD section 7.9, and the JFET input idea mentioned in this link: .

There is also a series "trap" configuration for measuring Q mentioned in EMRFD section 7.9 where you look for the null, but it seems it might not be as useful to measure self-resonant frequency.? Also, my Rigol DS-815 spectrum analyzer will automatically give you the -3dB points on the peak where the tank circuit resonates. If anyone has input on why I should consider the trap method over the tank circuit method which aren't mentioned in EMRFD, please let me know. EMRFD does state that the null may be easier to measure on some spectrum analyzers.

Steve WA6ZFT