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Re: YIG device failure modes
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Tobias,
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The main coil is for pretune -- which brings the center frequency of the YTO to the YTO PLL's capturing range which is usually +/- 20~30mhz around the CF. The FM coil is used to perform the phase locking. HP also feeds LF from the loop filter to the main coil path to help DC tracking and pretune. I would worry more about the FM coil's tuning sensitivity and modulation bandwidth which have great effects on the closed loop dynamic. The tuning sensitivity is easy to measure yourself but the modulation bandwidth is not. The idea is to make sure the FM bandwidth (which translates to a pole in the open loop transfer function), is 10 times higher than the PLL's open loop bandwidth. Good luck! Calvin ---In hp_agilent_equipment@..., <tobias.pluess@...> wrote :
Jeff, re-fitting a different YIG was an option which I was thinking about when I repaired my 8341A sweeper. The YIG is a 5086-7323 which operates from 2.3 to 7GHz and tuning coil sensitivity is 24mA/GHz. However, I wonder how accurate those 24mA/GHz are. For
instance, if I fitted another YIG with 20mA/GHz, would that work as well? the YO driver used can be calibrated for offset and gain... Have you ever fitted a replacement YIG? What about those SYTMs HP has used sometimes (switchable YIG tuned multiplier)? is there any replacement? And do you have an idea what the reason could be for the semiconductor to fail? assuming the operating voltages were ok, is there some chemical aging process or so which destroys the semiconductor some day? because there are instruments which are 30 yrs
old and still working, but the older they get the more difficult it will be to find spare parts I guess; if the YIG fails and cannot be replaced, the whole instrument is nothing more than a really heavy paperweight.... Tobias HB9FSX -------- Original message -------- From: "kmec@... [hp_agilent_equipment]" <hp_agilent_equipment@...> Date: 10/16/17 06:01 (GMT+01:00) To: hp_agilent_equipment@... Subject: Re: [hp_agilent_equipment] YIG device failure modes ? I have tested several hundred YIG devices over my career. (Have drawers full of them, its a sickness)? I have seen more misaligned YIG support rods or bad oscillator semiconductors than I have seen bad coils. ? Sometimes the coil connection fails at the solder point due to wire wrap/crimp failure and current heating the joint, eventually it opens, have fixed three like this. Some model YIGs have high coil current and if poorly cooled/heatsunk, the enamel insulation
seems to fail and create a sorted coil. Only have seen one like this, but opened it up and figured out the failure. ? Other times, the polystyrene rod that holds the YIG sphere warps & twists over time from heat?& general plasticizer failure?and misaligns the magnetic axis of the sphere with the field, pretty tough to fix this, major cause of holes and high end tailing
off. And, of course, when the semiconductor device fails (Gunn diode in older X band and up, Bipolar thru 12 GHz for old ones, FET now), you are done. ? It is possible to re-fit different YIGs into various pieces of gear, but re-scaling the drivers to the right coil sensitivities can be challenging/time-consuming. ? The worst thing to deal with is the wideband? YIG tuned multipliers. Never had much luck bringing these back to life once they go south. ? YMMV Jeff Kruth WA3ZKR ? In a message dated 10/15/2017 1:40:13 P.M. Eastern Daylight Time, hp_agilent_equipment@... writes: ? |
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