[time-nuts] hp5061A questions

David Kirkby david.kirkby at onetel.net
Wed Jun 1 07:15:28 UTC 2005

Dave Carlson wrote:

> Absolutely. Especially don't mess with any of the mechanical adjustments on
> the A4 harmonic generator that is attached to the CBT. These are aligned to
> resonate exactly to 9.192 GHz and it would be almost impossible to realign
> one without using a special waveguide tuning fixture. Only a few of the
> extrusions are intended for matching the A4 to each individual CBT.
> If you've already turned some of the knurled screws, nuts, knobs, and hex
> screws, you may never be able to capture the correct resonant peak, even if
> you can get the cesium oven to start working.
> The best remedy to a mis-aligned harmonic generator is to find another one
> that has not been adjusted and attach it to your CBT, or send it to someone
> with the correct waveguide fixture.
> Dave Carlson

As a matter of interest, from someone who knows next to zero about 
cesium sources, but a reasonable amount about radio frequency and 
microwave engineering, what does the waveguide tuning fixture do? What 
is so special about it? Could an amateur fabricate one?

X-bade rectangular waveguide suitable for 9.192GHz is easy to come by 
(known in the UK as WG16, but also as WR80 and RG52). I used that very 
waveguide as a child in a 10GHz amateur radio system with a Gunn diode.

Tuning of waveguide components can be achieved by inserting screws in 
the side - again not too hard to fabricate.

My guess (and note I have never seen a cesium source) is that the 
waveguide fixture would temporarily be part of the cavity, so if the 
dimensions of that fixture were known, it would not be hard to make it 
oneself with access to a milling machine, or get a small engineering 
company to do it.

I appreciate from reading what you have said that not touching the 
assembly is the best idea, but if someone has "tweaked" one, I would not 
have thought getting the cavity back on resonance would be hard, given a 
few physical dimensions, and a microwave power meter. Waveguide to N 
adapters are pretty easy to fabricate too, although again I suspect they 
can be bought used for very little. And microwave power sensors with N 
connectors are easy to come by, or again could be made easily.

Just more curious than anything else, as I don't have a cesium source, 
and don't feel I will ever become a real "time-nut" and get one.

Soon I should have my bit of kit built which will have both a 
10811-60111 and a Standford PRS10 both locked to GPS. I'm sure the two 
oscillators will drift relative to each other, so I know I'm going to be 
questioning which is the most stable, but I think I will stop before 
buying a cesium source.

David Kirkby,

Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/

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