The application of phase-locking techniques to the design of, apparatus for measuring complex transfer functions

The theory of phase-lock synchronization is given briefly. Two devices for measuring complex voltage ratios are described. In the first, which has a frequency range 1¿110 Mc/s, the voltage ratio to be measured is converted to a constant intermediate frequency of 450 kc/s. The frequency difference between the signal generator and the local oscillator is kept constant by coupling the tuning shafts mechanically and by a phase-lock synchronizing device; special means for extending the pull-in range, making use of a coarse and fine electronic adjustment, are described. The second instrument has a frequency range of 30¿700 Mc/s, and here the local and signal generators are free-running and are separately tuned manually. A double frequency conversion system is used. The frequency of the second local oscillator, by means of a phase-lock device, is kept 450 kc/s below the frequency difference of the signal and first local oscillator. A description is also given of how the complex measuring results can be displayed on a cathode-ray tube.