[time-nuts] Fast risetime pulse generator

Morris Odell vilgotch at bigpond.net.au
Fri Apr 15 22:21:43 UTC 2016


Hi all,

Brooke Clark wrote:

> In the HP 5100 Frequency Synthesizer they use a heater on the SRD in order to increase it's 
> lifetime so that the 3 MHz drive will generate the needed harmonics. http://www.prc68.com/I/HP5100.shtml These 
> assemblies are no longer available and getting an SRD with a lifetime long enough to work with a 3 MHz input is a common 
> as chicken teeth.  A solution is to get a large stud mounted Varactor and these do have long lifetimes.

I was so pleased to see this. It mirrored my experience exactly. A few years ago I restored a 5100A and its 5110A exciter. The SRD heater in the 5110A had developed a failed thermostat and was a charred blob. I made up a test jig and tested lots and lots of different diodes and as it turned out, the best candidate was a stud mounted varactor out of a junked transmitter from the old VHF cellphone system. It's worked like a charm ever since. This post (and webpage) has explained it beautifully.

Morris






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