A while ago I bought a 8970B noise figure meter but never got it running due to a bad YTO. Recently, thinking it would be interesting to play with, I bought another for parts, figuring I would make one good one.
To my surprise, internally they are quite different! The YTO in the second one is completely different, with an entirely different frequency range. Hmmm, that¡¯s interesting...
It turns out that the second unit has option 20, meaning it can go to 2 GHz. I am amazed how different these units are internally!
In any case the initial problem in the second unit appears to be in the controller which usually doesn¡¯t run at all. Or maybe power supply, I haven¡¯t dug into it. The unit was dropped hard at one point in its life as the back panel where the transformer is mounted is bent so I¡¯m going to look for a mechanical cause for the problems and instead of looking to fix the first unit concentrate on the option 20 one. Hopefully the YTO wasn¡¯t damaged in the drop.
It is just interesting to me that the slight increase in the top end frequency required such massive RF system changes.
Peter
