Stephan, I have a DMTD system that was built by NBS (now NIST) in the early 80s.
The coarse phase shifter is made up of ten lengths of miniature coax cable bundled up in a shielded box with toggle switches on the front panel to select the delay used. The LSB is about 2us. It also has a fine adjust that consists of a couple varactors in a phase delay circuit. I have found that with a good quality offset L.O. I can get the precision I need (<1X10-13th at a 1 second interval) without using the fine adjust circuit. As far as the small time interval value I usually start my measurements at around 2 to 4 us delay with the DUT set for a slowly increasing phase shift, The accuracy required depends on what your measuring but with a 10Mhz input and a 1hz beat note +-1us is equal to +-1X10-13th so most counters will work just fine. Just be advised that the us and below digits will be jumping around quite a bit! Also make sure that the delay is adjusted so the counter updates every second, you can be updating every two seconds which nullifies the cancellation of the noise in the L.O. Corby Dawson ____________________________________________________________ Always a good call. Click now to establish your local phone service! http://thirdpartyoffers.juno.com/TGL2141/fc/BLSrjpTHbDiki6pTvGTKKCArqOqjNQCdDWO6HMJXAtNrfARisO7WahgNOso/ _______________________________________________ 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.
