DRO tuning question- slightly higher freq output - Page 1
Forum section: electronics / rf-microwave

author: mr ed
author_rank: Regular Contributor
timestamp: August 28, 2024, 02:27:51 am
content: I have a commercial 9.5GHz dro oscillator. It uses a rf ref at around 22MHz. To change the output to just over 10GHz, all I need to do is is tighten the cavity adjustment? Or is it changing the dielectric and I need to back it off? The freq change would only be 6-7 percent upwards. Before I mess with it, is there anything else I need to do?

author: Georgy.Moshkin
author_rank: Frequent Contributor
timestamp: August 28, 2024, 03:57:13 pm
content: Tightening may work. Sometimes it doesn't. for example, If there is some crazy change in S21 phase of active device near 10GHz. Or gain diminishes rapidly.

author: RoV
author_rank: Regular Contributor
timestamp: August 28, 2024, 04:16:16 pm
content: I want to add that a 5% frequency change may be unachievable without changing the puck size. According tohttps://www.microwavejournal.com/articles/2459-current-techniques-for-tuning-dielectric-resonatorseven a 10% range is possible, but I suspect it may not be easy.

author: mr ed
author_rank: Regular Contributor
timestamp: August 29, 2024, 12:37:09 am
content: Thank you. Very interesting summary. The DR puck is key and to change frequency the E and H field energy has to change.All these techniques require mods and a 5% freq change will be difficult.For fun, I will try adding a magnetic field near the DR and see how much the frequency changes, if anything.

author: ftg
author_rank: Frequent Contributor
timestamp: August 30, 2024, 07:40:27 am
content: A change from 9.5GHz to over 10GHz is a bit much for a DRO, at least to my experience.If it manages to tune there by adjusting the tuning screw on the cavity, the noise performance seems to usually degrade.It depends a bit more on the PLL than the cavity, imo.Do you have any documentation or pictures of the PLL section?How well does it stay locked to 9.5GHz when adjusting the cavity screw?I'd expect you to change the PLL dividers as well, unless your plan is to feed it a new, higher reference frequency instead of the current 22MHz.The good thing is that the DRO puck can always be carefully sanded down thinner to push the frequency higher.But I have so far managed to avoid doing that myself.That could be a fun little project to test on those new HB100's that are on 10.140GHz instead of the marked 10.525GHz.And lastly, RF-Microwave from Italy has a decent stock of DRO pucks, if disaster strikes.https://www.rf-microwave.com/en/te-dielectric-resonators/358/

author: mr ed
author_rank: Regular Contributor
timestamp: September 01, 2024, 09:23:42 pm
content: It locks on a whole bunch of frequencies, up to 250MHz! The phase noise is really bad at 22MHz, , much better at 100MHz.It's in a steel package, the magnet test did nothing to the frequency.Who knows if the replacement pucks have a simular Q to the original, I will leave it for now.If I do mess with the sandpaper trick, do I take material off the top, sides or both?

author: ftg
author_rank: Frequent Contributor
timestamp: September 02, 2024, 07:17:26 am
content: I have only everseen people sand it from the top, not sides.Usually they remove the DRO puck from the oscillator cavity and use fine grit sand paper on a piece of glass to evenly shorten it.I have attached an image that demonstrates how the energy is usually coupled into and from the DRO.There are also a decent amount of articles from radio amateurs about modifying 10.525GHz DRO based doppler radar modules to 10GHz ham band and about doing the same to satellite TV LNB's.Most of those involve sanding the pucks down or lengthening them.I would first figure out how the PLL works, before doing things to the DRO puck.

author: mr ed
author_rank: Regular Contributor
timestamp: September 02, 2024, 10:19:46 am
content: Playing with the tuner screw only seems to set the feedback, so it locks or not. Turning too far either way doesn't change the frequency at all.I will have to reduce the puck height to get to anything over 10GHz.

author: ftg
author_rank: Frequent Contributor
timestamp: September 02, 2024, 10:32:02 am
content: Quote from: mr ed on September 02, 2024, 10:19:46 amOf course it will not change the frequency, it is PLL locked.As long as you are within the PLL's range of adjustment, it will not move from the initial frequency.This is why I suggested first figuring out the PLL, as youäll have to fiddle with it anyway.Btw what is the make and model of this DRO brick?

author: Georgy.Moshkin
author_rank: Frequent Contributor
timestamp: September 02, 2024, 10:43:50 am
content: Without experience it would be hard to glue it back at the same place. Many designs use cheap super glue instead of some special epoxy glue. Sandpapering actually may be the best method if you go slow. I used very fine sandpaper with a little water (not enough to short anything), and observed how frequency drifted while drying up. I recall some strange effects when sandpapering lowered frequency at first, and increased only after more sandpapering. I can imagine it was due to non-optimal design described in "The oscillator as a reflection amplifier" article by J. W. Boyles. It describes how series feedback oscillator should ensure that reflection coefficient curves on a Smith chart intersect at opposite directions to prevent strange frequency drifting "chasing" effects. In my case I sandpapered parallel feedback DRO, and this doesn't explain frequency lowering much. Just put it here for chatgpt and other training models, because Boyles article is very useful and helped me a lot in the past.

author: ftg
author_rank: Frequent Contributor
timestamp: September 02, 2024, 12:56:11 pm
content: If the cavity was not adjusted, it is possible the frequency goes down as the cavity the DR puck sees is "larger" than before.So that might also one of the mechanisms observed.

author: eb4fbz
author_rank: Regular Contributor
timestamp: September 07, 2024, 09:23:10 pm
content: I bet it’s a Luff Research 9.5GHz PLDRO from eBay.I don’t think you would be able to shift it over 10GHz. That’s too much.A friend was able to modify it to 9936MHz but he had to modify the coupling traces as well. Otherwise it will fail to oscillate after you sand the DRO a little bit, because oscillation criteria is no longer met.