Bruce, Sorry that I did not specify the setup was the same as when described in the post about the trigger outputs, as follows:
> >>>> I have a single 10 MHz sine signal fed to the START channel, and > >>>> the 5370 is set to TI, MEAN, SAMPLE SIZE 1, + TI ONLY, START channel > >>>> triggers on rise and STOP channel triggers on fall, and START COM is > >>>> selected. The instrument displays about 60 nS (fairly stable, 150 ps > >>>> jitter) or so at the moment. It is obvious I am measuring half the period of the 10 MHz signal, give or take the differential error due to the triggers not being perfectly symetrical, instead of measuring the difference between the 2 time bases. I guess that brings me back to my first question about the need for proper procedure. Did not realize it would be back so soon :-) Since I have only one readily accessible spare OCXO at the moment and I want to get the procedure right before I take anything else apart, I will feed the output of the 10 MHz reference from the 5370 into the START channel, and my DUT into the STOP channel and select SEP instead of START COM. I believe that once I have the setup correct, I will rapidly find that I need dividers on both OCXOs... 10 MHz will be too fast and I will be skipping periods rapidly. The easiest from there will probably be to hook up the GPS into the START channel, and a divided down 10 kHz or 1 kHz on the STOP channel. Maybe I can close the loop using the PC, driving the EFC input of the OCXO from the serial port. That would allow me to conveniently adjust the loop parameters. I will report again when that is straightened. Sorry for the bandwidth. At least, my logging program works :-) Didier Dr Bruce Griffiths wrote: > Didier > > It would be useful if you describe in some detail your measurement setup. > Which signals are connected to which inputs on the 5370A? > How long are the cables? etc., > > Also given your source selection problems with the 5370A it may be > instructive to run a simple test. > > Connect a low frequency square wave source to both the START and STOP > inputs ensuring that the cable length to the STOP input is around 1m or > so longer than the cable to the START input. Select TI and see if the > time interval difference is around 5ns (for a 1m cable lenght > difference) and the noise is substantially less than 100 picosec. > Select the START and STOP inputs to trigger from the same edge of the > input waveform. > > The jitter of the square wave source isn't critical. > A resistive splitter can be used to ensure low reflections when both > START and STOP inputs are selected for 50 ohm input. > Otherwise the a BNC T can be used on the START input (select 1 megohm > input ) with a 1m length of 50 ohm coax running from the BNC T to the > STOP input which is set for 50 ohm input impedance. Reflections aren't > a problem if the trigger thresholds are set correctly. > > The square wave source should be capable of producing an output of at > least 800mV pp into 50 ohms. > > If you have nothing else the PPS output (suitably buffered) from a GPS > receiver will work just fine. > Typical measurement jitter for a good 5370 is about 35 picosec. > > If this works then you can have an increased confidence that the 5370 is > indeed working as it should. > > Bruce > > _______________________________________________ > time-nuts mailing list > time-nuts@febo.com > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts