Computer Control, Signal Detection and Amplification

The Gunn oscillator frequency-lock became progressively more unstable as its slewing rate increased, whether caused by rapid frequency stepping or by the application of FM. We found ourselves limited in practice to a stepping time of 50-100 ms and an FM deviation of 10 MHz at a rate of 1 kHz. This was considered reasonably satisfactory in that a complete scan could be completed in a few seconds and that our signal detection rate 2 kHz was close to the frequency at which manufacturers, e.g. Millitech, specified their detector performance. The same FM rate was used whether our detector was a Schottky barrier mixer diode or the helium-cooled bolometer. 

The output from the 2 kHz phase detector required much less attention, other than care to ensure that neither the detector input nor the DC output overloaded either instrument. Normally these parameters and the detector phase controls would be set up at the start of a day s work and would need no further adjustment unless gross changes were made to the MMW source frequency. 

The devices are all static electricity sensitive as mentioned in Chapter 2. One 

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