With a good number of YIG oscillators (YTOs) around, time for a few tests. Rather than writing down all the numbers, a quick test setup, with two power supplies, an EIP 545A counter (with built-in power meter), an Agilent 66319D power supply (used as current source for the main tune and FM coils of the YTO), a 14.5 dB attenuator (just happens to be the value I had around) and a few cables.
When performing such test, make sure to put a 10 dB (or larger) attenuator of really good quality (low SWR) directly at the YTO output, without any adaptors or cables in between – some YTOs will show inaccuracies of not properly terminated in 50 Ohms.
This is a view of the setup:
![yiga 1](https://www.simonsdialogs.com/wp-content/uploads/2016/06/yiga-1.jpg)
![yiga 2](https://www.simonsdialogs.com/wp-content/uploads/2016/06/yiga-2.jpg)
One of the YTOs under test, a S081-0320 2 to 8 GHz Avantek part.
![yiga s081-0320](https://www.simonsdialogs.com/wp-content/uploads/2016/06/yiga-s081-0320.jpg)
![yiga frq vs current](https://www.simonsdialogs.com/wp-content/uploads/2016/06/yiga-frq-vs-current.jpg)
![yiga pwr vs ghz](https://www.simonsdialogs.com/wp-content/uploads/2016/06/yiga-pwr-vs-ghz.jpg)
As you can see, the output frequency is pretty linear vs. main coil current.
![yiga dev from lin vs frq](https://www.simonsdialogs.com/wp-content/uploads/2016/06/yiga-dev-from-lin-vs-frq.jpg)
The tests are carried out first with increasing coil current, then with decreasing coil current, and the hysteresis is calculated (difference of output frequency, when a approaching from higher vs. lower current).
![yiga hyst vs freq](https://www.simonsdialogs.com/wp-content/uploads/2016/06/yiga-hyst-vs-freq.jpg)
One thing to watch out for are thermal effects, but let the YIG warm-up for 1 hour or so, with the main coil at half-range current. The effects aren’t all that big for the Avantek YTO discussed here, but you never now, for lower quality parts, other manufacturers, and so on.