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PERFORMANCE DEGRADATION MEASUREMENTS OF AM VOICE COMMUNICATIONS RECEIVERS.
ROME AIR DEVELOPMENT CENTER GRIFFISS AFB NY
The degree of intelligibility at the output of a voice communications system is of prime importance to the system user. This report includes a discussion of the results of an in-the-house performance degradation testing program on two standard Air Force communications receivers operating in the A.M. mode. Performance degradation of the GRC-27 and GRC-86 receivers was measured using three methods. A listener panel was used as the standard of comparison. The Voice Interference Analysis Set VIAS and the Speech Communications Index Meter SCIM, both electronic systems, were also used. White noise, shaped noise or simulated speech, and a CW signal were used, at various power levels, as the interference. Without using the receivers, measurements at various SI ratios were made by mixing the signal and interference at audio frequencies so that a comparison of the performance of the VIAS and SCIM versus the standard Articulation test could be shown. Curves are contained in this report which show the equivalent A.I. reading for and A.S. for the types of interference used. In general, the results of all these tests show that the VIAS and SCIM are acceptable as intelligibility measuring devices, the amount of degradation depends on the SI ratio as well as the type of interference used, and interference which is slightly off-tune from the desired frequency may affect the intelligibility more than the on-tune case. Graphs showing these results are included in this report. Author
Interim technical rept. Aug 64-Dec 65,