weird trimmer related phenomena when tuning my YIG

[yefj]

Hello ,I have a very weird phenomena my YIG has a tune input.
When I used LD1084 regulator and one of the resistors was a trimmer even thow i put 10uF capacitors on the output and input .
When i try to tune my voltage going into the YIG the YIG starting to jumps 300MHZ 500MHZ back and forth.
So i suspect the TUNE voltage have jumps of 1V at least.
I suspect that when I changed the trimmer value it created this behavior.
A basic voltage divider get my YIG better stability then this thing.
1.Am i correct in my assumption?
2. Why the trimmer could create such a thing?
3.what could be manual tuning alternative for changing of resistor?

https://www.st.com/resource/en/datasheet/ld1084.pdf

 

[dick_freebird]

Trimpot may be more inductive than you think especially if wirewound. Even cermet body has a couple cm of overall loop length, what does adding (say) 10nH to each leg show?

Does the character of the instability suggest small signal (sine wave) or large signal (bang-bang or sawtooth)?

 

[FvM]

Is it an open loop setup (only YIG oscillator + variable supply) or are other tuning circuits involved? Do you have sufficient attenuation between oscillator and analyzer?