[time-nuts] OT: Levelled sine wave generator

[Bruce Griffiths]

David C. Partridge wrote:
> 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
>   
The phase noise wont be particularly low especially for low output
frequencies.

A diode double balanced mixer with dc current applied to the IF port is
useful as a wideband current controlled AGC device.

NB mixer IF response must extend to dc.

Bruce