Dual Mixer Time Difference Systems: Mixers

Mixer Port Terminations

To minimise the mixer noise contributions the mixer IF port should be terminated with a capacitor and the dc load resistance should be high. Both the RF and LO ports should be saturated.

To minimise mixer phase shift tempco the RF and LO ports should include series resistors to reduce their VSWR.

The Mixer IF port beat frequency waveform will be approximately trapezoidal when the mixer is driven and terminated as recommended. The slew rate at the beat frequency waveform zero crossings will be significantly greater than that with a sinusoidal beat frequency waveform of the same amplitude.

phase shift tempco

With 10MHz mixer input frequencies the equivalent phase shift tempco of a diode DBM can be as high as 10-20ps/C. This can be reduced significantly by minimising the mixer input port(RF and IF) VSWR. Even so the temperatures of the 2 mixers used in a DMTD should track to better than around 1mK or so to avoid degrading system performance. Using a higher mixer input frequency (100MHz) can reduce the mixer phase shift tempco to 2ps/C or less.


1) Environmental Effects in Mixers and Frequency Distribution Systems

Mixer Selection


Mixer Noise


Mixer Port Isolation


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