[time-nuts] OT: Levelled sine wave generator

Didier Juges didier at cox.net
Mon Dec 15 19:39:52 UTC 2008


Dave,

How about using a true signal generator?
I have not checked the spec for my HP 8657B (it's flat enough for what I
do), but it will do all that you are asking for, and being a true
synthesizer, it can be used for much more than just calibrate scopes. 

If flatness is not good enough, that could be addressed with an external
head, but all the signal generation and level control input is already
there.

Didier

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of David C. Partridge
Sent: Monday, December 15, 2008 9:19 AM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] OT: Levelled sine wave generator

Hi Didier,

I was actually considering an SG-504 to get the frequency range at the upper
end.    I has however hoping to better both that and the SG-503 by putting
it all in one for the complete frequency range and ideally having a better
generator as as well.

Conceptually I was hoping to aim for a capbility similar to the Tegam SG5050
(sort of like a "grown-up" version of the SG5030 but with a frequency range
extending up to 2.5GHz (I only need 1GHz though).

D.

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Didier
Sent: 15 December 2008 12:29
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] OT: Levelled sine wave generator

Dave,

You may want to look at the SG-503 Tektronix plug-in for a levelled sine
generator. It goes to 250 MHz, and the full service manual with schematics
is on my web site in the Manuals pages:

http://www.ko4bb.com/cgi-bin/manuals.pl

I have one and it works as advertised. Great for scope calibration, not so
great as a signal generator :-)

Didier KO4BB 

> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of David C. Partridge
> Sent: Monday, December 15, 2008 4:04 AM
> To: 'Discussion of precise time and frequency measurement'
> Subject: [time-nuts] OT: Levelled sine wave generator
> 
> 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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