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 signals over wireless communications paths from a multiplicity of transmitting antennas;

receivers which receive said interlaced test signals by means of a multiplicity of antennas and determines measurements of amplitude versus frequency and phase shift versus frequency characteristics of the multiple propagation paths from each transmitting antenna to each receiving antenna; and

a signal processing circuit which use one or more of said measurements to correct for effects of the multiple propagation paths on the communications;

wherein test signal receivers comprise:

one or more signal generators producing facsimiles of the multiple transmitted test signals wherein said generators are adjustable and can have an initially unknown time offset from a transmitted test signal, an unknown frequency offset from a transmitted test signal, and an unknown time base of generation from a transmitted test signal;

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

a logical processor capable of analyzing said downconverted signals and providing control signals to said adjustable facsimile signal generators to remove the initially unknown time offset, the initially unknown frequency offset, and the initially unknown time base of generation between the transmitting antenna injected signal and the receiving antenna facsimile signal.