Spectral purity requirements for UHF LOS/SATCOM transmitters

As the number of communications users in the UHF band increases, especially in times of conflict or during large-scale, inter-service training exercises, the purity of each transmitter must be controlled to allow peaceful co-existence of friendly forces, both for line-of-sight (LOS) and satellite communications (SATCOM) operation. Increased data demands also cry out for greater bandwidth as imagery transmission requirements surface, thus making spectrum conservation more demanding. As the number of mobile platforms continues to reduce and the number of communicators aboard each information disseminator platform increases, the problems of co-site management are magnified, all of which demands even greater spectral control. We start by focusing on in-band and later expand to out-of-band spectral requirements. The in-band (within the assigned communication channel itself) requirements center on frequency accuracy, uplink Doppler correction and phase noise. The effects on AM/FM operation are examined, followed by phase shift keying (PSK) operation. The effects of vibration, which greatly influence phase noise, are calculated. These in-band requirements are then summarized and shown to be met by careful radio design. We conclude by focusing on the control of the main contributor to close-in interference, which is adjacent channel interference for SATCOM operation