Hi If you have two inputs into the mixer, one comes from one OCXO and the other comes from another OCXO.
If you set the EFC voltage on one or the other OCXO so the output of the mixer is zero, the inputs are 90 degrees apart. At that point the mixer has a maximum phase sensitivity and the carrier is surpassed. Bob > On Oct 1, 2016, at 7:44 PM, Bob Stewart <[email protected]> wrote: > > Hi Bob, > Can you tell me what you mean by "just put the two inputs in quadrature, > attach to a sound card and you have all you need for phase noise."? What > inputs do you assume I have? I don't think I can attach two 10MHz inputs to > a soundcard and expect anything useful. > > 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 6:24 PM > Subject: Re: [time-nuts] Measuring phase with an HP 3456A? > > 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.
