Ways to keep resonator stable

[yefj]

Hello , I am building a PLL based on a resonance frequency of a two port cavity resonator .
The resonator is a basic cylindrical resonator with sapphire core and the inputs and outputs are coupled the basic coax cables .

I have found a resonance with a very high Q.
For some reason the resonant frequency slightly moves all the time which breaks my pll loop because it’s suppose to be a stable source .
what could cause a drift in the resonant frequency ?
How can make the resonator more stable ?
Thanks.

 

[volker@muehlhaus]

what could cause a d rift in the resonant frequency ?
How can make the resonator more stable ?

A friend is building very high Q resonators for his oscillators with world record phase noise.

The resonator issues that I remember:
- temperature drift of the cavity and dielectric resonator
- pick up of external vibration

Keeping the cavity at constant temperature is easy, mechanical decoupling of the cavity from the environment is not so easy.

 

[yefj]

Hello Volker,regarding what you said:
My oscilator is a big block of copper shown below connected in two port system.

1.What methods are there to reduce mecahnical decoupling?
1.What methods are there to reduce thermal drift?
Thanks.

https://www.artisantg.com/info/Agilent_E4407B_Manual.pdf

https://www.keysight.com/il/en/assets/9018-05248/user-manuals/9018-05248.pdf?success=true

 

[D.A.(Tony)Stewart]

A friend is building very high Q resonators for his oscillators with world record phase noise.

The resonator issues that I remember:
- temperature drift of the cavity and dielectric resonator
- pick up of external vibration

Keeping the cavity at constant temperature is easy, mechanical decoupling of the cavity from the environment is not so easy.

attaboy to the attasecond jitter record.

I had a similar task of decoupling 100g shock/ 5g vibration and 50g acceleration from an HC-cut OCXO to meet 1e-10 stability criteria for Doppler. Only allowed 5mm of space, in 1976 I ended up using ESD foam for CMOS which had the necessary low Q resonance yet poor durability. It was just for Black Brandt rockets.

Dual ovens make that task easy.

Identify the source of sensitivity and protect it.

 

[yefj]

Hello , given my bulky iron cylinder of a resonator , in what way you recommend me to deal with heat drift ?

 

[volker@muehlhaus]

1.What methods are there to reduce mecahnical decoupling?
2.What methods are there to reduce thermal drift?

1. Uncouple the oscillator by placing it onto a foam material, for example. Replace your semi rigid cables by soft cables. In other words, reduce coupling of shock and vibration to the cavity.

2. You can heat your cavity to a controlled (regulated) temperature, similar to OCXO for crystal oscilators.

 

[yefj]

Hello semirigid are very good rf cables.
What do you recommend for a soft rf cable in X band?
Thanks.

 

[FvM]

What's time scale and amount of observed drift? It sounds unlikely that a resonator on lab table is exposed to vibrations or larger temperatur variations. I rather guess that instability is caused by your PLL loop. Considering the complex circuit topology, it's not simple to distinguish drift causes.

strategy for designing a locking component in PLL

Hello,there is a circuit shown below taken from the attached article, where we put a YIG signal to a cavity resonator(from A to B) . Then for feedback we lock on the point of the dip. this dip is supposed to be a resonance of a cavity. resonance is when the magnetic energy equals the electric...

www.edaboard.com

If it's actually a mechanical problem, e.g. broken resonator, you should observe huge effects when slightly knocking it.

 

[D.A.(Tony)Stewart]

The lack of VCO spectrum or scope info is rather disappointing. It seems you presume we are clairvoyant.