The SNV-12, Signal and Noise Voter, uses Digital Signal Processors to continuously monitor multiple remote receiver sites and select the receiver with the best signal quality. A typical application is an LMR system in which mobiles and portables can hear a repeater, but due to their lower transmit power, the repeater can’t hear them.
Remote receivers can be positioned in the communications dead spots, with audio from each receiver linked to the SNV-12 voter. It will select the best quality signal from all unsquelched remote receivers and forward this signal to the repeater for rebroadcast and/or monitor by a dispatcher, thus providing greater talk back range for the field radios.
The SNV-12’s Site Voter Modules (SVMs) use a spectral approach to continuously monitor the audio signals from each receiver site, using proprietary speech detection and measurement algorithms. These algorithms continuously calculate a 31 discrete step Signal Quality Number for each voting receiver. The SNV-12 monitors all SVMs and votes the site with the best Signal Quality Number.
This thorough voting process ensures the best site is voted even if the received signal is transmitted by a vehicle currently moving behind buildings or between remote voting receiver sites.
The SNV-12 voting criteria may be easily optimized. DSP voice detection capability allows automatic faulting of receivers with inappropriately open squelches. The voting process is initiated whenever any receiver is unsquelched, signaled either by loss of idle/pilot tone or by a hardwired COR output or multiplexer E-lead; individually configurable on each SVM. The SNV-12 accepts pilot tones of either 1950 or 2175 Hz.
The PTG-10 pilot tone generator is available for use with receivers that lack idle tone capability.
Application Note: Use of Voter Comparators to Improve Railroad Radio Communications