Development of an IF-Signal Transmission and Distribution System for the 65m Telescope of the SAO

The 65m radio telescope of the Shanghai Astronomical Observatory (SAO) is an advanced radio-telescope system which has a large aperture, a high frequency limit for detection, multiple frequency bands for observation, and an antenna movable to any sky direction. Because of the site of the telescope, the distances from its receivers to its digital terminals are nearly 500m. It is thus an issue to accurately transmit radio signals received by the telescope antenna. In radio astronomy it is a common practice to first convert received radio signals to proper Intermediate-Frequency (IF) signals, and then transmit the IF signals through coaxial cables to a terminal room, where the IF signals are distributed to multiple terminals and monitoring equipments. The distribution also requires highly consistent division of single-channel signals into multi-channel signals. Meanwhile, the needed powers of signals input to different terminals are different; it will be convenient to correct for attenuations of signals input to various terminals, respectively. In this paper, we present the design and implementation of an IF-signal transmission and distribution system for the 65m radio telescope, which has a frequency range for observation of 0.1GHz to 2.5GHz and a channel number of 6. The signal-attenuation correction range of the system is 1dB to 30dB, and the correction can be controlled on-site or remotely. The specifications of the system, including link gains, VSWR, isolation levels, and consistency levels in distributed outputs can meet the demands. These enable the system to provide high-quality IF signals usable as inputs of the digital terminals. We have carried out tests and verified the high-level performance of the system. Overall, the system can meet the needs of radio-astronomy observations of the SAO.