DEVIATION MONITORING AND FEEDBACK TO IMPROVE COVERAGE
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2002-Jan-14
For a Frequency Modulated (FM) signal the range or coverage. However, when the transmitter car- recovered message signal amplitude is directly related rier is 60 dB or higher than the noise (C/N), adjacent to the modulation index or deviation of the transmitted channel noise is reduced with a reduction in the FM signal. Thus, keeping the modulation signal at the maxi- deviation. The optimum system would decrease trans- mum designed deviation value would result in the highest mitter deviation to the minimum for strong C/N condi- received signal to noise (S/N) ratio. When a transmit- tions (C/N > 60 dB), and increase transmitter deviation ter is at the threshold range of a communications sys- to the maximum for weak C/N conditions. tern, maximum deviation is desirable to provide the most Sinad = signal + noise + distortion noise + distortion Figure 1 is a measurement of receiver Sinad versus levels close to the noise sensitivity limit (Sinad = 12 dB). a trunking transmitter signal deviation for three carrier The inbound trunked deviation limits are noted in figure Deviation vs SINAD 20.00 C/N - 7 dB C = -115 dBm DELTA -120 dBm -125 dBm 0.