Replace YIG with modern VCO in old SA? - Page 1
Forum section: electronics / rf-microwave

author: toastedcrumpets
author_rank: Regular Contributor
timestamp: May 09, 2020, 12:12:09 am
content: My first RF repair was an 8591A spectrum analyser, I even did a video on it:https://youtu.be/WFnWgubNcEYThe issue was a failed YIG oscillator and I got a replacement from a spares unit; however, I'm now thinking about trying to repair the spares unit (there's a nice LCD conversion kit on eBay I can use to give it it's missing screen).I can't source these YIGs on eBay, plus it seems they're prone to failing after long use. What are the other options? I've seen technical papers on replacing YIG oscillators with more modern VCOs, is this something any one has tried? My main worry is the response for the frequency control loop. Anyone got any other suggestions or advice?

author: MadTux
author_rank: Frequent Contributor
timestamp: May 09, 2020, 12:57:45 am
content: Find someone with a wirebonder and get the failed transistors replaced?https://www.qsl.net/ct1dmk/wbond_ex.htmlYIG replacement would probably be a bad hackjob, I doubt the other oscillator has the spectral purity/phase noise of a real YIG. Frequency control probably also needs major modifications, YIG coil current drive amplifiers would be obsolete and would need to replaced as well.

author: TheMG
author_rank: Frequent Contributor
timestamp: May 09, 2020, 01:22:02 am
content: You'd be opening up a can of worms with that. There likely isn't going to be an off the shelf VCO module you can just drop in and have it work. Very likely a lot of external support circuitry will be needed to interface correctly with the rest of the instrument and achieve the desired response characteristics.At the very least, you would need to re-calibrate the instrument and even then without extensive testing there will be no guarantee that the performance is going to be up to par with the original manufacturer's specifications.This would be a rather challenging project even for someone very experienced with RF and spectrum analyzers or test instruments in general.

author: coppercone2
author_rank: Super Contributor
timestamp: May 09, 2020, 02:58:00 am
content: also be careful of thermal tracking, if you start changing technologies out you might get different drifts, the instrument may have been designed to drift in the same dimension as the YIG (common design "feature" to reduce cost)

author: eb4fbz
author_rank: Regular Contributor
timestamp: May 09, 2020, 02:06:11 pm
content: It's not possible to get the same bw and phase noise performance of a YIG using a single VCO.It would be probably easier to replace the full synthesizer than just the oscillator.

author: toastedcrumpets
author_rank: Regular Contributor
timestamp: May 09, 2020, 02:31:50 pm
content: Hi all,Thanks for the input, quite a lot of negativity around the suggestion for a VCO. I'm not alone in considering this though:https://www.analog.com/en/technical-articles/replacing-yig-tuned-oscillators-with-silicon.htmlAdmittedly they're trying to sell VCOs...I should also say this is a fun project, I'm not trying to sell the unit to some poor victim or improve its performance, just figure a way to bring it back to life while learning about RF. If there's another route for the repair I'd happily follow it. Does anyone know how I can source "compatible" YIGs?Regarding the wire bonding suggestion, if even Shahriar from the signal path doesn't have one in his palatial lab then I don't hold much hope for me finding one or operating it...Regarding the discussion around calibration/temperature dependence etc, the 8591A has a sampler for feedback on the YIG frequency so provided I can plumb into that we should be good. I'm even thinking about making fake YIG current loads out of shunts that I map into voltage control for the VCO.Keep the ideas and feedback coming, thanks!

author: coppercone2
author_rank: Super Contributor
timestamp: May 13, 2020, 04:41:18 am
content: what is so hard about wire bonding?There might be a difference between building something that takes a while to setup to do a few wires once a year vs some kind of lab thing you have a technician sit down and use on company demand and whimactually curious as to how hard it is to do for a simple IC (not like a MCU with 100 wires)if you get rid of ease of use/setup time, and ultra high reliability that a fab has, how hard is it really? (I assume they are often used in very time critical and very results critical locations which make them extra expensive).I seriously ask this because the zombie analyzers we all run are so shady that some non spec wire bond is probobly the least of our problems, there are probobly other things way more likely to break sooner then spending all this effort worrying about a great wire bond. beware of the signal path, RF STILL WORKS without all the best stuff, thankfully.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: May 13, 2020, 05:58:44 am
content: Quote from: toastedcrumpets on May 09, 2020, 02:31:50 pmConsider reaching out to a local EE department at a university. If they have an IC group, they might be able to do wirebonding inhouse.

author: toastedcrumpets
author_rank: Regular Contributor
timestamp: May 13, 2020, 06:39:08 am
content: I actually work at the local university and there's no other for around 2.5 hours drive away. Unfortunately our EE department focuses on the algorithmic side of networking rather than the RF. We have an excellent EE workshop but they stop at component level, rather than subcomponent(?) level repair.I've looked into wirebonding before, without a machine its pretty hard to get positioning and force levels right. I have a side project I'm working on which is repurposing DaVinci EndoWrist surgery tools into a microscopic workstation to see if I can do really small component work, but even with that I don't think I'll be able to do wire bonding. For a start I'd need a better microscope than my stereo setup...

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: May 13, 2020, 07:01:00 am
content: Well, I wish you the best of luck. I can ask the technicians at my group for some info, we have some really skilled wirebonders.

author: toastedcrumpets
author_rank: Regular Contributor
timestamp: May 13, 2020, 07:27:37 am
content: Quote from: TheUnnamedNewbie on May 13, 2020, 07:01:00 amThanks! Once the endowrist station is up, at the very least I'll be able to explore the exposed circuitry inside the YIG and test for things like continuity in circuit. If I really find the issue and its repairable I might reach out.I'm still considering creating my own equivalent module out of a modern VCO, but I think I'll put it on the shelf for a bit unless someone has previous experience or a better suggestion.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 13, 2020, 08:51:25 am
content: There are modern VCOs, but there is a difficulty to get a large tuning range and low phase noise at the same time. One may need way more than just one VCO to replace the YIG.

author: toastedcrumpets
author_rank: Regular Contributor
timestamp: May 13, 2020, 10:11:50 am
content: Quote from: Kleinstein on May 13, 2020, 08:51:25 amIf you check out the link below, that's exactly what modern VCOs do, they have an array of VCOs and switch between them in various bands.https://www.analog.com/en/technical-articles/replacing-yig-tuned-oscillators-with-silicon.html

author: coppercone2
author_rank: Super Contributor
timestamp: May 14, 2020, 04:27:43 am
content: I think you might be able to do this with micrometers and low displacement living hinges (like in a scale)Like if you use a beefy micrometer as a fine adjustment to position a living hinge after you get it in the general position with a micrometer actuating a slide rail you activate. Surgical stuff sounds like it needs to be fast. This can be slow as hellEasier since it is basically on a grid, so you only need 2 axis, not three. To make a micropositioning tool you get a metal like aluminum and cut special channels in it, so it deforms when you pinch themthe force would be unknown but it would be repeatable I think, so you can adjust it

author: toastedcrumpets
author_rank: Regular Contributor
timestamp: May 14, 2020, 07:14:03 am
content: This is what the medical system is like:https://youtu.be/81KqrTJfhusI think it's too clunky for wire bonding, plus there's no premade wire bonding attachment/nozzle. Plus, even with a wire bonding setup this assumes the problem is there and I can find an appropriate replacement part... I think this is a dead end for now and will pursue the VCO approach