Most of the discussion on Time interval counters is about averaging many measurements to achieve a subnanosecond resolution. It is possible to achieve subnanosecond single shot measurement resolution with a time interval counter if one uses a time to digital converter (TDC) chip. Suitable TDC chips are available from http://www.acam.de/ <http://www.acam.de/> In particular the TDC-GP1 has a resolution of better than 250picosec with a range of 200 millisec, which should be more than adequate for measuring the time delay between GPS and local standard derived PPS pulses. All it needs is a microprocessor to process the data and transmit it to a computer for logging. The TDC-GP2 has a range of 4 millisec and a singlr shot resolution of about 65 picosec. Although these chips are a little pricey at around the 100 euro mark they are a lot cheaper than an Agilent/HP 53131 or its equivalent.
It is possible to build a USB device that time stamps a PPS pulse with a 65 picosecond resolution and a measuring range of centuries. A PIC18F4550, a TDC-GP2 and a 74AC164. The 74AC164 synchronises the PPS pulse to the local high stability clock, the TDC-GP2 measures the synchroniser delay and the synchroniser output transition samples the PIC's internal timers. The PIC timer is clocked by the high stability clock and software extends the effective counter length to 64 bits or whatever length is desired. Bruce _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
