The system operates with a signal transmission/reception apparatus such as a receive antenna, or a coaxial system or the like, while the antenna is receiving information signals and it operates by injecting a low power pseudo-noise digital signal into the antenna and detecting reflected energy, the magnitude of which depends on the condition of the antenna. The reflected signal is processed and compared with the original test signal to produce a digital number representing the condition of the antenna. The digital number is compared with a table of numbers in a processor to determine the condition of the antenna.