[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




More information about the time-nuts mailing list