a test signal injector which interlace test signals with communications signals, wherein one or more of the test signals is an FM sweep;

a transmitter which transmits said interlaced test signals over a wireless communications path;

a test signal receiver which receives said interlaced test signal and determines measurements of amplitude versus frequency and phase shift versus frequency characteristics of the propagation path; and

a signal processing circuit which uses one or more of said measurements to correct for effects of the propagation path on the communication signal;

wherein the test signal receiver comprises:

an adjustable test signal facsimile generator which adjustable signal can have an initially unknown time offset from the transmitted test signal, an unknown frequency offset from the transmitted test signal, and an unknown time base of generation from the transmitted test signal;

a downconverter which uses said facsimile signal to heterodyne said received test signal to obtain a down-converted signal; and

a logical processor capable of analyzing said downconverted signal and providing a control signal to said adjustable facsimile signal generator to remove the initially unknown time offset, the initially unknown frequency offset, and the initially unknown time base of generation.