[time-nuts] OT: Levelled sine wave generator
David C. Partridge
david.partridge at dsl.pipex.com
Mon Dec 15 10:03:54 UTC 2008
Sort of related, but only just - however the signal to noise ratio here is
so good that I feel impelled to ask.
For 'scope calibration I'm considering building a levelled sine wave
generator.
Ideally the specs I'm looking for are:
o Close to DC (10kHz or 100kHz would be fine) up to at least 1GHz.
more would be better but not critical
o Output levels from 0.5Vp-p(-2dBm) to at least 4Vp-p(+16dBm) into 50R
(up to >6Vp-p(say +20dBm) would be better)
o Output flatness levelled within 2% of desired output level (+/- 0.086dB)
across the entire frequency range at the final connector to the DUT
This will almost certainly mean an external levelling head.
o Modulation - not critical, FM or AM might be useful.
o A logarithmic sweep capability might be nice, but isn't necessary.
o Frequency display - nice to have but output to external counter is OK.
Generating the basic signal is probably just a case of using something like
an HP VTO-8200, mixing it with 2GHz (Mini-Circuits RMS30?), low pass filter,
an AGC stage (see below) and then amplify probably using an MMIC like the
Mini-Circuits ERA-2SM followed by an additional stage to get the extra few
dB. For more accurate frequency control some sort of synthesiser locked to
a reference might be in order (I had to get a time-nuts hook in here
somehow).
The question is what should go in the sensor head?
Logically I need to sample a proportion of the signal delivered to the
output connector, compare the output of the sensor against a DC reference
level telling it the desired output level, and feed back a voltage to a
wideband AGC stage (any suggestions for this?) in the main unit. I also
need to be able to detect that output is not levelled.
Or should I just forget the whole idea and go talk to R&S with a large
cheque in hand?
Cheers
Dave
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