[time-nuts] Problem with HP 83623A 20 GHz sweep generator stepping up/down 100 Hz when not wanted.

Brooke Clarke brooke at pacific.net
Thu Dec 22 15:56:19 EST 2016

Hi David:

Some time ago I built an automated mixer test system where I first attempted to use HP 8350B sweep generators as the 
sources for the LO and RF inputs, but this failed to work because at the narrow bandwidth settings on the HP 8566 
spectrum analyzer there was way too much phase noise, so I switched to synthesized sweep generators made by HP and 
Wiltron, but I forget the model numbers.

The SA was operated at it's narrowest IF bnadwidth (100 Hz?) and I don't remember seeing any amplitude variations, 
whereas when the 8350 was used the amplitude jumped wildly.

So I expect the problem is in the transverter.

Have Fun,

Brooke Clarke
The lesser of evils is still evil.

-------- Original Message --------
> I run a test over the weekend with a fellow radio ham. I transmitted 100 mW
> or so at 10368.115 MHz from an HP 83623A 10 MHz to 20 GHz sweep generator
> http://www.keysight.com/en/pd-1000001862%3Aepsg%3Apro-pn-83623A/synthesized-sweeper-10-mhz-to-20-ghz-high-power?cc=GB&lc=eng
> into a small horn antenna inside my lab.
> He was able to receive me about 7 km away, although the signal was quite
> week - it was 20 dB above the noise in a 2.9 Hz bandwidth.
> What is odd, is that his transceiver + transverter combination indicates
> the signal generator is shifting frequency up/down 100 Hz. This is not slow
> drift, but a step change - see waterfall picture, where time is on the
> vertical axis, and frequency is on the horizontal. Unfortunately I don't
> know what the scale is on the vertical axis - I am trying to find out. The
> frequency on the x-axis is not the true frequency, but that shown on an 2 m
> amateur transceiver, so the true frequency is more than 10 GHz higher.
> The step size on this HP sweeper is 1 kHz, so the 100 Hz up/down shift is
> not due to a rotary encoder that might be just on the limit of two
> frequencies.  Both the internal oscillator and a GPS locked frequency
> standard were used during this test. Going from internal to external
> reference caused a 450 Hz step in frequency, but did not change this
> up/down 100 Hz behavior. So the problem is certainly not the crystal in a
> 10 MHz reference oscillator, as two have been tried, one of which was
> locked to GPS.
> Does anyone have an idea what may cause this behavior?
> Does anyone have any ideas on the best way to investigate this, given the
> signal is at more than 10 GHz?
> What I do *not* have is any other signal generator capable of operation at
> 10 GHz. The only other sig gen I have is a 30 MHz Stanford Research DS345
> function generator.
> I don't have a TI counter at the minute, but had an offer of $300 accepted
> on eBay for a 5370B a couple of days back, so should have a TI counter
> soon. (Yes, I have had an 5370B and SR620 in the past, but for various
> reasons no longer have them). The 5370B at $300 was a lot cheaper than an
> SR620.
> Other equipment I have include
> * 22 GHz spectrum analyzer
> * 30 MHz signal generator
> * 20 GHz VNA
> but no other signal generator capable of anywhere near 10 GHz.
> I do have a couple of double balanced mixers which have RF and IF inputs
> that will take 10 GHz, and an IF output that will go from DC to 4 GHz.
> Introducing a REALLY long delay might allow the steps to be seen, as the
> frequency at the LO and RF inputs of the mixers will be different. But
> that's not really practical, as I'd need an awfully long bit of coax.
> The 20 GHz vector network analyzer, which could be pressed into service as
> a poor (rich) mans microwave signal source, but I suspect the output of
> that is quite dirty, as the output is generated from a step recovery diode.
> I have not yet tested it on a spectrum analyzer, but the SA has quite a few
> spurious signals, so I'm never exactly confident of the SA. But one thing
> to possibly is
> * Set sweep generator to 10.368 GHz
> * Set sweep generator to 10.378 GHz, so there's a 10 MHz difference.
> * Mix the VNA + sweeper down to 10 MHz using a double balanced mixer
> * Compare the 10 MHz at the output of a mixer to that of a 10 MHz crystal.
> Steps of 100 Hz should then be seen I guess.
> Any better suggestions?
> Someone had kindly given me a key to change the step size of the signal
> generator from 1 kHz to 1 Hz. I've not applied that yet, as it is quite a
> complex procedure. But the fact the step size of this is 1 kHz, but it is
> shifting up/down 100 Hz, does not make sense. Especially given the unit is
> capable of 1 Hz resolution, but HP decided to charge extra for 1 Hz steps.
> Luckily this is just a software option.
> I did wonder if the signal generator was incapable of output the exact
> frequency needed, so it was stepped up/down periodically so it gave the
> right number of cycles over a long duration. But again, the fact it can
> step 1 Hz with just a software upgrade suggest that's not the case.
> The radio ham that noticed this step change in frequency is well used to
> listening on 10 GHz, and hearing beacons. So I think its reasonable to
> assume that the problem is not his end, but my end.
> Any thoughts, which do NOT include purchasing a second expensive 20 GHz
> signal generator. They are around $10,000 each, so a bit out of my price
> range.
> Dave
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