-------- In message <capnvnruderci4sulhb9djjf7sqwixa5ovarjwteylpoht+m...@mail.gmail.com> , Anders Wallin writes:
>I ran some tests on a new 53230A counter that just arrived: >http://www.anderswallin.net/2015/04/keysight-53230a-noise-floor-test/ Anders, I think that setup didn't measure what you think. When you feed the counter EXT REF from the same source you measure, all the transitions will happen at a certain point relative to the internal clockcycles of the counter, and therefore be subject to only one of many possible noise-situations. A much better way: Use the "good" signal for your CH1/CH2 inputs, and also feed it to a slightly offset synthesizer generator for the EXT REF. If you feed the EXT REF 10.0001 MHz (relative to CH1/CH2, the absolute value is not really important) then over a period of 10000 seconds your test-setup will sweep the internal clock-cycle of the counter at least once. Then plot the MIN/MAX/STDDEV of the measurement versus time and you will discover that the noise floor is not even close to being even. If you find a particular good spot and want to use it for measurements, the way to go is to tune the length of the cable for EXT REF (or use a tweakable delay line) -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [email protected] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ 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.
