The technique I used to measure the PN contribution of the LTC6957-4 at 10Mhz Low noise 10MHz sinewave OCXO (Trimble 37265 removed from Thunderbolt (Thunderbolt has rather noisy output amplifier)). OCXO PN measured against a pair of similar OCXOs via correlation using the TimepodConnected to low noise RF amplifier (push-pull transformer feedback CB Norton amplifier NF ~ 2dB Z10043 from Clifton Laboratories) with a gain of ~12dB.Output (~19dBm) from amplifier is split by a minicircuits 1:2 splitter (Minicircuits ZFSC-2-4)3dB 50 ohm passive attenuator reduces one output to ~ 14dBm this is connected to the Timepod reference input. The other output from the splitter is attenuated with a passive 50 ohm attenuator to the desired input signal level for the DUT. The DUT output drives a minicircuits 1:2 splitter via a lowpass filter.Each of the splitter outputs is connected to either Timepod Ch0 or CH2 via an RF amp (in my case a HELA10-D) with a gain of around 10dB. Cross correlation ensures that the relatively high noise of the HELA10-D's isn't too significant, the trade off being that more time is required to average down their contribution to the measured noise. I use an RF power meter to measure the output of each HELA10-Dto ensure that the Timepod input signal doesn't exceed the maximum rated input for the Timepod. Alternatively if one has a sufficiently low noise amp like the Q-bit QB188 (NF ~3dB Gain ~ 15 dB) a single amp connected directly to the Timepod signal input via a passive attenuator should suffice. For most useful comparators or CMOS gates an ouput circuit like that on the LTC6957-4 evaluation board should suffice.
Bruce _______________________________________________ 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.
