VSWR protection circuit apparatus

摘要

A VSWR protection circuit employs first and second mixers whereby the first mixer receives at one input the transmitted frequency and has a local oscillator coupled to the other input to provide at its output a difference frequency. This difference frequency is applied to the input of the second mixer which also receives at another input a frequency which is the sum of an undesired EMI signal plus a residue signal due to reflection from the transmitter. The second mixer produces difference frequencies according to the output from the first mixer. The output from the second mixer is applied to a narrow bandpass filter which essentially allows the transmitted frequency to propagate. The output from the narrow band filter is then detected whereby a DC control voltage is provided and used as a gain control for the transmitting amplifier and essentially is independent of most interfering frequencies.