Abstract :
Receiver and transmitter frequency control is accomplished by two phase comparison loops, The primary loop compares the phase of the receiver VFO with the output of a Crystal Reference System containing a total of 13 crystals and using three stages of interpolation to cover the required frequency range. The secondary loop, on transmit, uses the controlled receiver VFO for the sidestep function and a crystal stabilized reference oscillator, which is capable of being modulated, for phase comparison. The receiver-transmitter covers a range of 30-76 mc in two bands with 50 kc channel spacing. The control system is capable of handling +400 kc VFO setting plus drift error from nominal frequency. It employes transistors throughout and is capable of operation over a temperature range of -55 to +85°C. Thermistors and block filters are used to achieve gain and bandwidth stability. Receiver spurious frequencies due to the control system are down 85 db or more. Transmitter spurious radiation due to the control system is down 85 db or more except for a few channels near, the receiver i-f harmonic crossover frequencies, where the spurious radiation is down 75 db or more. High speed crystal switching has been achieved in the reference system allowing rapid, automatic change of channels. The receiver frequency control system occupies approximately 40 cubic inches and employs individually packaged printed circuit plug-in subassemblies. Total receiver and transmitter control system power drain is less than one watt.
