Tektronix 119-1140-01 (YIG filter used in Tektronix 492/494/2755 spec analyzer)? - Page 1
Forum section: electronics / rf-microwave

author: wb0gaz
author_rank: Frequent Contributor
timestamp: December 08, 2022, 03:05:02 am
content: (I don't know if this topic better belongs in test equipment, here, or elsewhere, so starting here and if moderator or other suggests ask elsewhere, will do that.)This device is a YIG filter (two SMA RF connectors and +/- DC coil voltage are it's only connections to the outside world.) It's used as a preselector (up to at least 21 GHz, the limit of the associated analyzers.)I picked it up at a ham swapmeet some years ago (sitting on the ground, with some surface deterioration, but turns out it still works normally, at least up to 18.5 GHz (coil current about 450 mA at that point, which is the limit of the test setup I had handy; the insertion loss there was about 4 dB which seems reasonable.)I am interested in whether I could use the device up to 24 (or better, 26 GHz). The application would be to perform single sideband selection for a noise figure analzyer downconverter (something akin to a homebrew version of the HP 8971C test set accessory for the HP 8970B noise figure analyzer) - the SSB filter improves noise figure measurements by reducing energy emerging from the DUT at the image frequency (the IF would probably be 1500 MHz, the ceiling of an stock HP 8970A analyzer.)Any thoughts on pushing the YIG filter device beyond it's expected ceiling frequency of 21 GHz?Presumably just a higher coil current would be involved, but concerned about possibly damaging the device - it was only $5 but I'd rather not jeopardize it.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: December 08, 2022, 04:37:27 am
content: Worth a try! Of course, how far you can go will depend on the internal structure and saturation point of the core. Eventually something will put an end to the fun, but there's probably a little bit of wiggle room and you can explore it reasonably safely by noting that at these current levels copper is a decent thermometer (0.4% resistance change per degree Celsius). Look up some magnet wire "enamel" temperature ratings, pick one sufficiently spicy for your personal risk tolerance, and watch with a voltmeter or set OVP accordingly. If you are quick with your measurements there is probably little risk, but if you want to park it at a high frequency power will become a consideration.Here is a YIG I measured the other day:https://github.com/jjoonathan/F3560R-YIG-Filter. You can see how power spikes as it saturates a few GHz above the rated frequency. Leakage also increases in that range; I can see why they gave it the frequency rating that they did.Best of luck with yours! EDIT: and be sure to let us know how it goes!

author: KE5FX
author_rank: Super Contributor
timestamp: December 08, 2022, 06:29:15 am
content: Good chance it will work. I'd be surprised if the modest overcurrent damages it. You will probably need to give it a good heat sink, though, and I wouldn't expect great insertion loss performance. A 4 dB penalty for NF measurements is already getting up there.

author: wb0gaz
author_rank: Frequent Contributor
timestamp: December 15, 2022, 04:02:42 pm
content: Finally got the (Wiltron 6653A) sweeper working enough to do this test -The Tektronix YIG filter seems to behave consistently up to about 24.5 GHz; beyond that (up to 26.5 GHz, limit of the sweeper here) the response gets broader/shallower (about 2x the passband width at 26 GHz vs 24 GHz) - I didn't attempt to quantify beyond that observbation.Coil current is about 600 mA at 26.5 GHz.Test signal level was approximately +3 to +5 dBm (less loss in the 20cm run of RG178 coax from sweeper output to YIG filter input).Used a Wiltron 560A SNA with a 18 GHz Wiltron APC-7 (adapted to SMA) detector so there could be artifacts there. I didn't have time this morning to set up a way to do comparison vs thru.The test setup is very crude and imprecise, but this was enough to tell me that the YIG filter doesn't suddenly die (temporarily or permanently) undergoing this test, and is probably usable to just above 24 GHz, but probably not much beyond that.KE5FX comment re preamp is well taken - I believe the HP 8971C (which I'm seeking to mimic in some way, without automation) I believe has a front end preamp (as it uses a YIG filter as a preselector.)