HI
DMTD = Dual Mixer Time Difference Single Mixer = what is commonly used for most things. If you have a single mixer setup, just put the two inputs in quadrature, attach to a sound card and you have all you need for phase noise. Bob > On Oct 1, 2016, at 4:30 PM, Bob Stewart <[email protected]> wrote: > > Hi Bob, > I don't have a DMTD breadboarded up for testing. This was just a test of the > new LPF using only a single Mini Circuits ZLW-1H DBM, and things kind of > progressed from looking at the output of the LPF on the scope to "I wonder > what I would see on the 3456A?" sort of thing. I'm running a > holdover/recovery test on the code and hardware changes to get a reliable > 1PPS from my GPSDO, so there is some very slow movement over the range of 0 > to 100ns. > > Bob > > From: Bob Camp <[email protected]> > To: Bob Stewart <[email protected]>; Discussion of precise time and frequency > measurement <[email protected]> > Sent: Saturday, October 1, 2016 3:14 PM > Subject: Re: [time-nuts] Measuring phase with an HP 3456A? > > Hi > > What is the beat note coming out of the DMTD? > > Put another way: > > DMTD involves three oscillators. Two are on roughly the same frequency and > the third is > offset from the other two. The difference frequency is typically something > like 10 Hz. > It does not *have* to be 10 Hz, but that is one way to do it. > > So, moving on using 10 Hz (which may be wrong): > > If you are at (say) 10 Hz, you get a 1x10^6 “error multiplication” on the > output. One cycle > at 10 MHz gives you one cycle at 10 Hz. The one cycle is 10% of 10 MHz, it’s > 0.1 ppm > of 10 MHz. You get a 10 degree phase change at 10 Hz for each 10 degree phase > change > at 10 MHz. > > The 10 Hz offset limits your phase noise process. The upper (or lower) > sideband wraps around > at 10 Hz and then starts dumping back into the other sideband’s data. You > also need to have a > signal processing chain that will tolerate the carrier being “in band”. > Between the two … not > such a great way to do it. > > It’s *much* easier to simply hook up a single mixer (half of what you have > already) and look at > the two sources in quadrature. Then the sidebands line up. The carrier is > gone. The dynamic > range can be *much* less. > > Bob > > >> On Oct 1, 2016, at 2:32 PM, Bob Stewart <[email protected]> wrote: >> >> I've been spending a small amount of my time looking into making a sort of >> hybrid DMTD with a pair of DBMs up front feeding the stereo input to a sound >> card. So, I got the 100KHz LPF back from Oshpark and hooked it up to my >> scope for verification - an obvious step. Then I hooked it up to my 3456A >> just for grins. (The two DBM inputs are 10MHz outputs from two different >> GPSDOs). So, as I watch this, I think the obvious question: can this >> measure phase angle better than the 5370A? I guess I need to send it >> through a full 100ns of phase change to get a calibration value. So, who's >> been down this road and what did you discover? >> Bob >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
