[time-nuts] DMTD Question

Bruce Griffiths bruce.griffiths at xtra.co.nz
Tue Jan 26 09:51:08 UTC 2010


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




More information about the time-nuts mailing list