[time-nuts] Re: Phase noise with a lock-in amplifier.
phk at phk.freebsd.dk
Sun Apr 17 14:28:34 EDT 2005
In message <4262A4F2.6010508 at onetel.net>, David Kirkby writes:
>So if the two inputs are fed to a mixer have different path lengths, the
>inputs to the mixers will *not* be identical.
Right, but I think there are much easier ways to measure it. For
instance, send the signal into one of the modern high-speed A/D
converters (65MHz, 14 bits) and do a FFT on the result.
(If you want to try this, check out the "USRP" which Matt Ettus built
for the GNUradio people: http://www.ettus.com/)
>I'm pretty sure if you low-pass filter the output of that mixer, you
>will see the oscillator phase noise shifted from 10MHz down to near DC.
Mixing highly correlated (or as in this case: identical) signals is
far from a trivial undertaking.
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
More information about the time-nuts