Thermal sensitivity of a DMTD used in a composite clock

We present the thermal effect on the DMTD (Dual Mixer Time Difference) and its ZCDs (Zero Crossing Detectors) used in the composite clock. This composite clock is based on servoing a VCO by both a cesium beam clock and a hydrogen maser. We obtain an output signal which combines the long term stability of the cesium clock, the middle term stability of the H maser and the short term stability of the VCO. The stability of the DMTD system and its ZCDs at 100 MHz must be about 10^-15@1s for the system. The stability of the output signal depends on the VCO stability. This paper describes the effect of the thermal variations on the DMTD and the ZCDs. We explain how to decrease or eliminate the thermal sensitivity of the DMTD system.