Digital microwave radio signatures for 16 QAM modem testing

Microwave signatures that result from testing digital microwave radios under conditions of severe multipath fading have been studied. From tests performed on various types of radio equipment it is shown how variations in the signature can be related to linear amplitude distortion and group delay distortion. The information is used to verify the correct adjustment and operation of digital microwave radio equipment as it is manufactured. Tolerances for linear amplitude distortion can be checked and it can be ensured that the signature meets certain minimum requirements. Measurements have been made on 16 QAM (quadrature amplitude modulation) radio equipment of different designs. Tests were also done to compare signatures for multipath fade at the SHF and at the IF