A wonderful analog signal generator


This page is devoted to one of the better signal generators available to the amateur user, the HP-8640B.

I got mine from Canada and, thanks to Jan Skirrow, who helped me picking it up, packaging and sending it to Spain, now I can generate nice signals from 0.45 to 550 MHz (at +20 to -145 dBm), modulated in AM and FM both with internal generated signals or with an external source. The stability and accuracy of the generator are really good. I have used it to check sensitivity of my receivers... Some can hear signals as low as -140dBm!. It is also very useful to check the S-meter calibration. And to align rigs with a signal with a very low phase noise. Definitely, a handy gadget to have in your home lab!

Repair works

I got my HP-8640B with a known failure, as it generated a nice signal but the counter indication was wrong in all except a couple ranges. Thanks also to Jan, who provided e-mailed scanned schematics, I tracked the problem down to the range selector assembly, which is very easy to get out of the generator (the generator is built in a very nice way, with easy removable cards and assemblies).

Range selector assembly

Here is a view of the 8640B without the range assembly:

Range selector location

It seems a common fault, but as this was my very first HP-8640B, I had no idea... Carefully looking at the range switch assembly, I found a missing finger in a rotary switch:

Missing finger in rotary switch

I found also a broken gear in this assembly (BTW, I need a replacement as it still works but I am afraid it will not last too much):

Broken gear

Broken gear (close view)

So, while I get a replacement (I hope to find it; please, let me know if you know where!), I managed to replace the lost finger with a DIY solution (made from a relay contact), as you can see:

Missing finger replaced

So now the generator is working and I just need to find a couple parts to get it really fixed. Any help on this will be appreciated!

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