[time-nuts] Phase Detectors/Mixers for DMTD and PN measurements

[Richard (Rick) Karlquist]

The HP 3048A phase noise system has a phase
detector in the HP 11848A chassis that was
originally a Watkins-Johnson (the original
company) M9H.  The M9H lives on now sold by
MaCom Technology Solutions.  "Someone" (unknown)
established that the Mini-Circuits JMS-5H
is an acceptable substitute, although not
an exact replacement.

The tradeoff in picking a mixer is the LO
level.  A high LO drive level such as the above
mixer have, gives higher performance, provided
you have a driving amplifier that has both the
necessary output power is itself low phase noise.
Depending on the test set up, some of the driver
amplifier phase noise will common mode out.

Also, high drive level mixers have a narrow window
between high enough drive to operate vs the damage
level.  So a third requirement on the driver
amplifier is that it's maximum output level is
less than the damage level.  (Don't ask how I
know this :-).  You can always put a pad between the
drive amplifier and the LO input of the mixer used
as phase detector to adjust the maximum possible
drive.

Rick N6RK