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

[Bruce Griffiths]

Richard (Rick) Karlquist wrote:
>
>
> On 11/23/2012 9:38 AM, Bruce Griffiths wrote:
>>
>> NIST have shown (at least at 10MHz) that the high level mixers they
>> tested are noisier than the ZRPD1.
>>
>> Bruce
>
> Do you have a citation to where they said that?
> What you quoted doesn't make sense, at least, out of context.
>
> We need to clarify phase detector sensitivity specs.
> For conventional (IE 50 ohm) phase detectors, it is
> apples vs apples to just go by the volts per radian number.
> However, mixers like the ZRPD1 artificially triple the
> voltage sensitivity by operating at 500 ohms, and using
> transformers to connect to 50 ohm equipment.  Doing this
> doesn't increase the possible signal to noise ratio.
> Consider this thought experiment.  Build your best 500 ohm
> phase detector and postamp.  Now replace with a 50 ohm
> phase detector and connect 3 postamps in parallel.  It is
> a wash.  Of course, you don't have to actually do this.
> You can simply use an op amp like the LT1028 with very
> low noise voltage.
>
> To actually put a 500 ohm detector on a par with a 50 ohm
> detector, the 500 ohm detector would need to use 3 diodes
> in series compared to one in the 50 ohm case.  With only
> one diode per arm, the maximum drive power utilization is
> considerably lower.
>
> Rick Karlquist N6RK
>
http://tf.boulder.nist.gov/general/pdf/2556.pdf

Where all the high level mixers measured have a higher phase noise than 
lower level mixers/phase detectors like the ZRPD1.

Bruce