Must be coupling in via the EFC, then. The phase shift does correlate precisely with the 1Hz LED. The EFC is just connected to the center tap of a 1meg pot, which is connected to +VREF and EFC shield. But, this is just for testing so I could trim the 1938 to my reference to check drift, of which there isn't a whole lot!
For a real circuit, I'll have to be a bit more careful, now that I know this isn't an internal loop artifact. The EFC sensitivity is higher than my trusty 105B's. > > The AFC loop (as opposed to EFC) is a purely analog loop in which there > is no mechanism for a 1 Hz oscillation. > > Now if you are talking about the EFC, that is another story. Depending > on how you are driving the EFC, you can pickup noise from any number > of sources. > > I vaguely remember there was an LED that flashed at 1 Hz if everything > was working OK. You might see if that is the source of what you are > seeing. > > > Rick Karlquist N6RK > Designer of E1938A > _______________________________________________ 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.
