If one carefully the value of a resistor in series with both the mixer
RF and LO ports and adds a 6dB attenuator between the series resistor
and the output of the associated isolation amplifier its possible to
reduce the mixer phase shift tempco by a factor of 10 or so. The
resistor value is chosen to minimise the mixer port VSWR for the given
IF port termination.
At 5Mhz this can reduce the mixer phase shift tempco to less than 5ps/K.
The mixer phase shift tempco also reduces as the input frequency
increases (at least up to 100Mhz or so) by a factor equal to the ratio
of the frequencies for which the phase shift tempco is being compared.
Thus carefully matching the mixer inputs can reduce the required mixer
temperature stability.
It is believed that the matching reduces the effect of reflections in
the input cables, so a similar effect may be achieved by using an
isolation amplifier located close to each mixer input port.
Bruce
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
