What are the main performance indicators of the receiver?

(1) Working frequency band. The receiver and transmitter operate in the same frequency range. During a hop, the receiving frequency of the current channel in the receiver matches the transmission frequency of the previous microwave station. This ensures seamless communication and efficient signal exchange.

(2) Local oscillator frequency stability. The local oscillator in the receiver must maintain high frequency stability to ensure accurate signal demodulation. This requirement is similar to that of the transmitter, typically ranging between 3 to 10 ppm.

(3) Noise figure. The noise figure of a digital microwave receiver is usually between 2.5 to 5 dB, which is lower than the typical noise figure of analog microwave receivers, which often exceed 5 dB. A lower noise figure improves signal clarity and system performance.

(4) Passband. To minimize interference and enhance signal quality, an appropriate passband with good amplitude and frequency response characteristics should be selected. The passband of the receiver is primarily determined by the intermediate frequency (IF) filter. For digital microwave systems, the passband is generally set to 1 to 2 times the symbol rate of the transmitted signal.

(5) Selectivity. The receiver must effectively suppress unwanted signals outside the desired channel. Strong selectivity is essential to handle adjacent channel interference, image interference, and self-interference caused by simultaneous transmission and reception.

(6) Automatic gain control (AGC) range. In free-space transmission, the received signal level can vary significantly due to fading. When the received signal is higher than the reference level, it's referred to as upper fading, and when it's lower, it's called lower fading. For digital microwave systems, upper fading is typically +5 dB, while lower fading can reach up to 40 dB, resulting in a dynamic range of 45 dB. The AGC must maintain a stable output level despite these fluctuations, ensuring consistent signal quality at the receiver end.