There is a cute way to use a scope. It requires a power splittere, a quadrature hybrid, and two mixers (all appropriate for the frequencies you are comparing), and an X-Y scope. Mini-Circuits sells appropriate parts. The stuff is hooked up like this:
X Axis S | H P ---- MIX ---- Y REF 1--L B -- REF2 I ---- MIX ---- R T | I Y Axis D The 'scope display will be roughly a circle if the frequencies are a bit different and the spot will go around CW or CCW depending on which Ref is higher. -John ============= > The only problem with the lissajous approach is you can't tell if your > OCXO > is high or low relative to the reference figure. This is resolved by > triggering the scope with the reference. If the trace is moving left to > right, the OCXO is high, and vice versa, IIRC (I just woke up). > Otherwise, > it works fine for fine adjustments aligning an unknown oscillator to match > a > known reference. > > Joe > > -----Original Message----- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > Behalf Of Geoffrey Smith > Sent: Sunday, July 25, 2010 2:58 AM > To: 'Discussion of precise time and frequency measurement' > Subject: Re: [time-nuts] Basic question regarding comparing two > frequencies > > Mark, > > I have been measuring the difference between a GPSDO and a HP 10811A TCXO. > To avoid any triggering issues I put the CRO into XY mode. The resulting > Lissajous curve figure flips at the rate of the frequency difference good > old Wikipedia has the maths. > > Just sit and watch the Lissajous and you can adjust the TCXO to have the > not > flip and set accuracies in small fractions of a Hertz. > > Geoff > -----Original Message----- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > Behalf Of Mark Spencer > Sent: Sunday, 25 July 2010 3:29 AM > To: time-nuts@febo.com > Subject: [time-nuts] Basic question regarding comparing two frequencies > > Hello: > > Just for grins I decided to compare the frquency from my GPSDO to the time > base > in my 5328A counter. > > > I connected the 10 mhz time base from the counter to channel A of my 100 > Mhz > > scope, fed the 10 mhz signal from my GPSDO into Channel B and with a T > adaptor > also fed this signal into the input of the counter. I scope to trigger > from > Channel B. > > > The drift betwen the two signals on the scope seems to match the error in > the > displayed frquency on the counter. (ie. if the counter shows 9999.9998 it > takes > approx 5 seconds for the the wave form on channel A to slip a full cycle > realitve to channel B.) > > > Is this a reasonable approach or is there a better way to compare two > frequencies using a scope ? > > Best regards > Mark Spencer > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.