On-Line Computer Tuned S-Band Phase-Lock Receiver

Abstract

Long-loop phase-lock receivers utilize a voltage-controlled crystal oscillator (VCXO) as the first local oscillator (LO). Tuning across a band of frequencies with such an arrangement has been virtually impossible in many of the existing space and satellite tracking equipments; the characteristics of the long-loop configuration have necessitated the use of VCXO's. One particular advantage of the long-loop, the capability of maintaining coherent LO and reference frequencies for coherent demodulation of all IF outputs, is a constraint on the receiver system described here. One approach for multi-channel operation has been to employ one VCXO for each frequency; this has obvious economic limitations in applications requiring many channels. For stations used in multiple vehicle tracking, frequency-agile or frequency-hopping anti-jamming applications, or for nearly unlimited tuning capability in a data gathering station it is desirable to use a frequency synthesis technique to tune the receiver. Such a synthesizer should lend itself to on-line computer control. It is the intent of this paper to describe a technique of digital synthesizer tuning for a long-loop S-band phase-lock receiver. Hardware utilizing this technique is now in operation at Marshall Space Flight Center and Kennedy Space Center. The synthesizer provides both direct-reading pushbutton and computer tuning; frequency changing can be accomplished in microseconds. The frequency band 2200-2300 MHz is covered in 0.1 Hz steps. Although capable of providing on-line computer controlled operation, the system is presently being operated in the manual mode.