Notes on the WJ-5008 YIG Oscillator

I wanted to take some high frequency measurements, so bought some Watkins Johnson YIG oscillators
and filters very cheaply on EBay. The WJ-5008 dates back to the early 1970's.

Unfortunately very little data was available on the net regarding the use of this device.

Spectral characteristics and coil sensitivity as well as a full theoretical description are here
and here The coil measured 12 ohm, so from the date the inductance is about 0.2 Henry, and the sensitivity should be about 25 Mhz/ma.

No pinouts etc were available.

I tried simply putting power to it (17 volt shown printed) with no result.

Next step was to pull it apart. It contained a PNP darlington, a TC thermistor, and a reverse connected schottky
diode for protection. The Gunn diode is mounted between two massive heat sinks.

The pins were as follows.

Coil:            pins 1 & 2

Oscillator:  pin 6 - 0 volt  and case/earth, pin 7 -17 volt (negative bias)
                   I measured about 12.6 volt across the Gunn diode.

FM              Looks like pins 8 & 7 , but I haven't tried them.

After resoldering a broken lead and biasing the magnet to about 8 gHz (it has no permanent bias magnet)
it sprang into life. It needs about 0.4 amps diode supply current - giving a wallplate
efficiency << 0.1% !

More modern oscillators use FET or BJT oscillators and need far less power, and some provide a much wider
tuning range.
It's still a very creditable performance considering it's nearly 40 year old, and it must have been a pace-setter when it was introduced.
These devices were used in various sorts of now obsolete aircraft radar scanners and jammers, which is probably
why user data is not readily available, and also why they available very cheaply.

It looks like a number of other WJ YIG oscillators have similar pinouts

I might also post some data on the WJ-643-21 four stage tuned filters at some stage.

Questions ?

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