[G0HZU_JMR]

I had a rummage in an old boneyard box of engineering samples, and I still have one of the early YIG filters. See below. This must be about 30 years old. This should be a 500-2000MHz YIG filter and I think it was about 15MHz wide. I'm not sure if it works though, it might be a dud.

The HP 8566A/B has a PRESEL PEAK button on it that allows the user to optimise the 2-22GHz YIG tuning at a given frequency. However, in my experience pressing this button can cause problems as it can cause dips in the YIG tuning at other frequencies. There is a button sequence that restores the factory default YIG calibration, and the default YIG cal works really well on mine. I try and avoid using the PRESEL PEAK button.

I've dug out my HP 8568B today and switched it on. It must be the first time I've used it in a few years. With the internal correction turned off, the various crystal RBW filters show a slight frequency error and also some amplitude errors (+/- 1.2dB between them), and some are not symmetric anymore. I do have the calibration supplement to the service manual, and this describes how to correct the LC and crystal RBW filters. The last cal sticker on it is dated 2006 and that must be about the year I bought it from the company. I'll have a go at aligning the filters today as I have some free time. It's too cold to go outside!