What are the main performance indicators of the receiver?

(1) Working frequency band. The receiver operates in coordination with the transmitter. During a hop, the transmission frequency of the previous microwave station becomes the receiving frequency for the same channel on the receiver, and the same frequency band is used by the transmitter.

(2) Frequency stability of the local oscillator. The local oscillator in the receiver must maintain high frequency stability, similar to that of the transmitter. Typically, the stability range is around 3 to 10 ppm, ensuring accurate signal reception without drift.

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

(4) Passband. To minimize interference and ensure optimal signal transmission, an appropriate passband must be selected based on both amplitude and frequency characteristics. The passband of the receiver is primarily determined by the intermediate frequency filter. For digital microwave systems, the passband is typically set to 1 to 2 times the symbol rate of the transmitted signal.

(5) Selectivity. The receiver must be able to effectively suppress unwanted signals outside its designated passband. This includes managing adjacent channel interference, image interference, and self-interference caused by simultaneous transmission and reception. Strong selectivity ensures that only the desired signal is received.

(6) Automatic gain control (AGC) range. Under free-space transmission conditions, the received signal level may vary due to fading. When the signal is stronger than the reference level, it's called upper fading, and when it's weaker, it's referred to as lower fading. In 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 system must ensure that the receiver’s output level remains stable despite these variations in input signal strength.