ELECTROMAGNETIC COMPATIBILITY BETWEEN SPREAD SPECTRUM AND CONVENTIONAL TELEMETRY SYSTEMS: THE KEY TO A NEW ERA FOR DOD TEST RANGES

Abstract

Telemetry operation is used extensively on a typical Department of Defense (DOD) test range to transfer data from an airborne transmitter to a ground receiver. The conventional telemetry systems employed are usually narrow-band systems. When a large number of airborne transmitters need to transfer data simultaneously to a ground station, a spread spectrum modulation scheme can be used. The drawback of such a scheme, however, is the large emission bandwidth required. The present frequency channeling plans in the telemetry band do not support frequency approval of large bandwidth data telemetry systems. However, a key requirement for obtaining the frequency approval can be satisfied if it can be shown that the spread spectrum modulated signal does not interfere with other systems in the same band. That is, the spread spectrum telemetry systems (SSTS’s) are feasible if these systems are electromagnetically compatible with the existing narrow-band telemetry receivers (NBTR’s) in their immediate environment. The electromagnetic compatibility (EMC between the SSTS transmitters and the conventional NBTR would promise the beginning of a new era for the telemetry operations on a DOD test range. This paper develops a methodology to establish the EMC between multiple airborne transmitters of an SSTS employing the code division multiple access (CDMA) technique and a ground-based conventional NBTR on a typical DOD test range operating simultaneously in the same band. The paper calculates the electromagnetic interference (EMI) levels between the SSTS and the NBTR to establish the EMC between the two systems.