curiousmarc
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HP Microwave Amp Module Goodness
🕑 Added 2020-10-24 23:35:55 +0000 UTCI recently bought yet another HP 8447F. Actually it came bundled in a very cheap lot that I got for another instrument so it is sort of a nice freebee. It contains two lab grade wideband amplifiers to 1.3 GHz. One of the channels (the preamp) passed the VNA test with legendary HP performance, almost perfectly flat across the band. The other one not so much, it was completely dead (unless you like 50 dB attenuators). So I gave it the ominous "THIS CHANNEL IS DEAD" sticker treatment.
It's supposed to be the "power amp" of the two, but not very powerful really, only 20 dBm (100mW), and the 1 dB compression point is at 15 dBm only. This channel is often dead in this instrument as enginerds and students alike abuse it with too much input power.
The defective amp is in its own module, so I opened it up to have a looksy, in case the damage was easily visible. No such luck. But behold, it's all HP hybrid goodness inside, with laser trimmed resistors, individual RF transistors, and lots of gold! Eminently repairable if you are an RF guru. I pinged Shariar at The Signal Path channel to see if he would be interested in reverse engineering it for us and possibly repairing.
Which of course makes no sense, as you'd be much better off replacing the entire module with an el-cheapo modern 4GHz or 6 GHz consumer grade linear amp, which may get you close to lab grade if you only use it up to 1.3 GHz and will certainly be a lot more powerful. But what's the fun and the learning in that?
Comments
Peter Larsen
If you keep this up, one would think you like old HP equipment or something.
Christian Giudici
Wow, the open preamp looks like a sci-fi device to non-analog techies ;) I am very excited for the video and the explanation of this circuit!
