Mystery YIG Oscillator

For a project I am currently working on, which I will detail here too eventually, I needed an oscillator capable of covering 8 to 12 GHz. There are quite a few of the miniature Stellex units on eBay, but they generally don't go much past 10 GHz. There are also tons of Avantek modules, in their standard round format, but a lot of them are custom part numbers with no specifications known. Since this particular project wasn't very sensitive to any of the parameters, I waited for a cheap one to show up with the right range and went for it. With a little investigating, it wasn't very difficult to determine the approximate specs for the module I purchased.

The particular oscillator I received is marked with model number SO8-0354 and is labelled for 7.9 to 12.1 GHz. It matches the first pinout in this old spec sheet. The closest standard units appear to be the AV-7871 through AV-7873, which cover 8 to 12.4 GHz with several different power outputs.

To determine the likely power output, I hooked the oscillator into a dummy load, then measured the current draw on the 15V input — it was almost exactly 125 mA, which means it is probably a 30 mW (14.8 dBm) unit.

Next, I measured the coil resistances. The tune port measured 10Ω and the FM port measured 1Ω. This makes the module's tuning behavior more like the next lower range, for example the AV-7403.

Satisfied that the module would behave somewhat as expected, I hooked it up to a spectrum analyzer. Before verifying the suspected power level, I used an inline attenuator to avoid any chance of damaging the machine. The analyzer allowed me to see the frequency move around as I changed the current on the tuning port. As expected from this helpful document, a fair amount of tune current was required before oscillation started.

With 395 mA flowing, a signal finally popped up at around 7.2 GHz. The lower edge of the specified range (7.9 GHz) was reached with approximately 450 mA. At the upper end of 12.1 GHz, around 670 mA was needed. This gave a tuning factor around 19 MHz/mA: in line with the specs of similar modules. I didn't test the FM port, but I suspect it would yield the 310 kHz/mA seen on the AV-7403.

Power levels seemed to vary between 7 and 13 dBm across a wide range, however the analyzer calibration may be off somewhat. A range of 6 dB matches the units on the spec sheet, but a 7 dBm minimum power is below that of any of the comparable modules. Perhaps that was another thing that made this part a special order. With the specs determined, I now have enough information to continue work on my project using this oscillator.

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1 Response

  1. 13 August 2014

    […] I used my mystery YIG oscillator and a function generator with a power transistor to sweep approximately 200 MHz around 10.5 GHz. […]

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