DEVIATION MONITORING AND FEEDBACK TO IMPROVE COVERAGE
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2002-Jan-11
For a Frequency Modulated (FM) signal the recovered message signal amplitude is directly related to the modulation index or deviation of the transmitted signal. Thus, keeping the modulation signal at the maxi- mum designed deviation value would result in the highest received signal to noise (S/N) ratio. When a transmitter is at the threshold range of a communications system maximum deviation is desirable to provide the most range or coverage. However, when the transmitter carrier is 60 dB or higher than the noise (C/N), adjacent channel noise is reduced with a reduction in the FM deviation. The optimum system would decrease transmitter devi- ation to the minimum for strong C/N conditions (C/N >60 dB), and increase transmitter deviation to the max- imum for weak C/N conditions.