Some time back there was a discussion on here about measuring complex (R
+ jX) impedance. I mentioned a vector voltmeter is a way I have done it
in the past. There is one on eBay at the minute
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4678&item=7514648769&rd=1
This is not the same model number I used, and I have not bothered
checking the specs as I don't want one. But something like this might be
a better bet than cheap 'amateurish' meters I have seen around. But you
will need to understand complex numbers to make any use of it.
I'm not the seller, and have no connection with him/her, and live on a
different continent.
BTW, here is an interesting eBay auction. A *new* 2.7GHz frequency
counter, with a crystal in a temperature controlled oven for 59 UK
pounds (~$109)
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=40004&item=7515520015
Too good to be true? Well a check on the specs of the timebase makes for
interesting reading.
*Time base frequency : 10Mhz
Short term stability : +/- 3 x 10-E9 for 1 sec average
Long term stability : 2 x 10-E5 Month
Temperature : +/- 1 x 10-E5 ( 0C to 40C )
Line voltage : +/-1 x 10-E7 for 10% change*
Considering just the long-term aging, one year after calibration, you
could measure a 2m transmitter with an accuracy of +/- 34 kHz - although
to be fair, if you kept the oven on 24/7, the aging rate would almost
certainly decrease over time. (PS, you would also need to add to that
temperature drifts of +/- 1.4 kHz. on your 2m transmitter).
I have checked the specification with the seller, and he has confirmed
the crystal is in an oven, and double-checked those figures are correct.
All the other figures on the timebase are between 100 and 10,000x worst
than a decent ovened oscillator.
I guess you could use your rig to re-calibrate your oven-controlled
frequency counter periodically, although I thought it was supposed to be
the other way around. If the timebase has that performance, I suspect
the rest of the instrument is built to similarly exacting standards.
I'll keep looking for an HP counter on eBay. Anyone in the UK got an HP
5342A, 5343A, 5350B or similar with GPIB that counts to at least a few
GHz they want to sell? An oven would be nice, but is not essential, as I
have a rubidium atomic standard and hope to soon lock that to a GPS
receiver.
-----------
David Kirkby,
G8WRB
Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/
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