[time-nuts] HP5065A Step Recovery Diode, what part#?

ed breya eb at telight.com
Tue Aug 28 20:07:12 EDT 2018

Most of my SRD stock resides on old junked PLO brick boards - that way 
they won't get lost, and I can possibly use some of the associated 
circuitry. I have quite a few good PLOs, and have used a number of them 
in various projects. The ones that I have from the 1960s -1980s seldom 
run the oscillator above about 2-3 GHz. The higher frequency types 
usually have a high power oscillator around 1-2 GHz, and tap off power 
to - you guessed it - an SRD multiplier, followed by a filter. For 
higher multiplication or power, there may be a class-C power amp stage 
in between. The highest fundamental PLO I have is around 3 GHz. 
Everything above that uses SRD multipliers.

So, I think the SRDs used in the sampler/PLL sections won't quite reach 
the Rb frequency, since they only need to be effective to around 1-2 
GHz, maybe 3. But, you never know - it may be worth a try.

The old PLO bricks are very popular I think, because they're useful, 
versatile, and easy to work on. They can usually be adapted for lots of 
situations and frequencies outside the nameplate. For example, about ten 
years ago I built a portable Rb standard unit, and I wanted to have 
decade frequencies as high as I could go. I had in stock a 9.6 GHz or so 
PLO that ran from 80 MHz reference. I took it apart and figured out the 
scheme. As I recall, it was an oscillator a little over 1 GHz, driving a 
power amp driving an SRD for around 8 or 9 times multiplication, then 
the filter. I modified it to run right at 1 GHz, added a tap for that 
output, retuned the filter for 10 GHz, and tweaked the SRD network to 
maximize output power there, for X10 multiplication. The reference drive 
needed no change - it uses 100 MHz from a VCXO locked to the Rb 5 MHz, 
and the 10 MHz comes from the PLL divider. So there you go - 10 MHz to 
10 GHz in one box. I couldn't have gotten the 10 GHz in there without 
this two-in-one source. It's no slouch either - the 1 GHz is about +15 
dBm, and the 10 GHz about +10 dBm.


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