[time-nuts] Best phase detector / mixer for 100MHz?

[Richard (Rick) Karlquist]

The old Watkins Johnson M9 series was the state of the art for
stacked diode mixers.  You can still get the M9E and M9H from
MaCom Technology Solutions.  The M9E is better, but only if you
have the 1/2 watt! of LO drive needed.  As you have done already,
it is probably possible to homebrew something like these.
There were a series of papers written by WJ people 20 years ago
or so in Microwave Journal or maybe it was Microwaves and RF
that explained all about these things.  These should be required
reading if you are going to homebrew.  Try to match the diodes
so you get low DC offset.  Some mixers also use resistors and
capacitors to assist the diodes; again read the WJ papers.

The horsepower race in phase detectors was somewhat rendered
unnecessary by the cross correlation techniques developed 10
or 15 years ago.  You can extend the effective noise floor by
dozens of dB this way.

Rick Karlquist N6RK

On 11/23/2012 7:42 AM, Anders Time wrote:
> I have been using an minicircuits mixer as a phase detector for measuring
> low frequency(5-10MHz) and it is usually good enough. But when I want to
> measure 100MHz the sensitivity of the mixer decreases a lot, so when I want
> to measure some really low noise 100MHz(Pascall -178dBc floor with 18dBm
> out) oscillators the sensitivity is not good enough. I read in an old
> article by Walls, Stein et al(Design considerations in state-of-the-art
> signal processing and phase noise measurement system) that one can use two
> diodes in series in the double balanced mixer to increase the sensitivity.
> I tried this with some standard 1n5711 Schottky and the sensitivity is now
> 1V/rad, but is there a easier way to do this? /Anders
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