[time-nuts] RF mixers for oscillator characterization, some questions

[Bruce Griffiths]

Pete wrote:
> Arnold,
>
> I have had good experience with the SYPD series
> from Mini-circuits. I have not seen any used, but
> their new cost is reasonable. They do several things
> well e.g. the DC offset on the units I received is
> <1mV & they produce >2V p-p when driven @
> +7dBm.
>
> Pete Rawson
>
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>   
Pete

These are OK except when one needs to isolate the IF ground from the RF
grounds to avoid low frequency ground loop problems.
The RPD and MPD through hole series are better in this regard as they
allow the IF ground to be isolated from the RF grounds.

The flicker phase noise characteristics of the mixer/phase detector
should be measured as some mixers/phase detectors have lower flicker
phase noise than others.
The termination of the IF port will affect the mixer phase noise. For
offset frequencies < 100kHz a capacitive termination of the IF port
which reflects the sum frequency back into the mixer reduces the mixer
phase noise. The tradeoff is that the mixer output at higher offset
frequencies is attenuated by the IF port termination.
Terminating the IF port in a capacitor reduces the RF port impedance, so
that a low value series resistor (22 to 39 ohms - select for lowest
VSWR) is then required to improve the RF port VSWR.
Terminating the IF port with a capacitor also alters the mixer gain (as
a phase detector) so this needs to be measured in conjunction with the noise

10514 and 10534 mixers using discrete diodes supposedly have lower
flicker noise than mixers using integrated quad diodes.


Bruce