Abstract: A performance monitor for use with marine radars which produces a visual indication upon the radar display screen only when the radar transmitter power, and the radar receiver sensitivity and tuning are within predetermined limits. An RF sample of the radar transmitted signal is mixed with a local oscillator signal and the resulting IF signal is coupled to an AFC loop which controls the frequency of the local oscillator. If the amplitude of the radar transmitted signal is above a threshold level, a single frequency response signal of fixed power is generated by the performance monitor and transmitted back to the radar antenna. A distinctive test pattern is produced upon the radar display if the radar receiver tuning is accurate and its sensitivity is sufficiently high.