Null initiated method and system for monitoring a priority channel

Abstract

A null initiated priority channel monitoring system provides enhanced nonpriority signal intelligibility and/or enhanced priority channel sensitivity during sample times. The priority channel or channels are monitored during nulls in the received nonpriority signal. The system can have a minimum time period between priority channel monitoring periods to avoid substantially continuous priority channel monitoring. The system can also have a maximum time period between priority channel monitoring or sampling periods to avoid missing any priority channel signal.

What is claimed is: 
     
       1. A method of monitoring one or more priority channels with minimal signal loss on nonpriority channels in a multichannel radio receiver, comprising: receiving a demodulated audio signal on a nonpriority channel;   detecting nulls in said received demodulated audio signal; and   sampling the priority channel for a priority sampling period for a received signal during each of said null to avoid disruption in said nonpriority received signal.   
     
     
       2. The method as defined in claim 1, including: setting a minimum time period between said priority sampling periods.   
     
     
       3. The method as defined in claim 1, including: setting a maximum time period between said priority sampling periods.   
     
     
       4. The method as defined in claim 1, including: receiving only said priority signal when a priority signal is detected during said priority sampling period.   
     
     
       5. The method as defined in claim 4, including: returning to receive said nonpriority signal when said priority signal terminates.   
     
     
       6. The method as defined in claim 5, including: pausing for a predetermined delay period when said priority signal terminates before returning to receive said nonpriority signal.   
     
     
       7. The method as defined in claim 5, including: scanning the priority and nonpriority channels sequentially when both said priority and said nonpriority signals have terminated.   
     
     
       8. The method as defined in claim 7, including: pausing for a predetermined delay period when said nonpriority signal terminates before scanning said channels.   
     
     
       9. The method as defined in claim 1, including: sequentially sampling at least a pair of priority channels during said priority sampling period.   
     
     
       10. The method as defined in claim 1, including: developing a relative audio null signal and comparing it to a predetermined null signal level to detect said nulls.   
     
     
       11. The method as defined in claim 10, including: varying said predetermined null signal level as a function of the amplitude of said nonpriority received signal.   
     
     
       12. A system of monitoring one or more priority channels with minimal signal loss on nonpriority channels in a multichannel radio receiver, comprising: means for receiving a demodulated audio signal on a nonpriority channel;   means for detecting nulls in said received demodulated audio signal; and   means for sampling the priority channel for a priority sampling period for a received signal during each of said null to avoid disruption in said nonpriority received signal.   
     
     
       13. The system as defined in claim 12, including: means for setting a minimum time period between said priority sampling periods.   
     
     
       14. The system as defined in claim 12, including: means for setting a maximum time period between said priority sampling periods.   
     
     
       15. The system as defined in claim 12, including: means for receiving only said priority signal when a priority signal is detected during said priority sampling period.   
     
     
       16. The system as defined in claim 15, including: means for returning to receive said nonpriority signal when said priority signal terminates.   
     
     
       17. The system as defined in claim 16, including: means for pausing for a predetermined delay period when said priority signal terminates before returning to receive said nonpriority signal.   
     
     
       18. The system as defined in claim 16, including: means for scanning the priority and nonpriority channels sequentially when both said priority and said nonpriority signals have terminated.   
     
     
       19. The system as defined in claim 18, including: means for pausing for a predetermined delay period when said nonpriority signal terminates before scanning said channels.   
     
     
       20. The system as defined in claim 12, including: means for sequentially sampling at least a pair of priority channels during said priority sampling period.   
     
     
       21. The system as defined in claim 12, including: means for developing a relative audio null signal and means for comparing it to a predetermined null signal level to detect said nulls.   
     
     
       22. The system as defined in claim 21, including: means for varying said predetermined null signal level as a function of the amplitude of said nonpriority received signal. .Iadd.   
     
     
       23.  A method of monitoring one or more channels with minimal signal loss on received channels in a multichannel radio receiver, comprising: receiving a signal on a first channel;   detecting nulls in said received signal on said first channel; and   sampling a second channel for a received signal in response to detection of at least some of said nulls, thereby avoiding disruption in said received signal on said first channel. .Iaddend. .Iadd.   
     
     
       24.  The method of claim 23, including setting a minimum time period between samples of said second channel. .Iaddend. .Iadd.25. The method of claim 23, including setting a maximum time period between samples of said second channel. .Iaddend. .Iadd.26. The method of claim 23, including receiving only said received signal on said second channel when said received signal is detected during said sampling. .Iaddend. .Iadd.27. The method of claim 26, including returning to said first channel when said received signal on said second channel terminates. .Iaddend. .Iadd.28. The method of claim 27, including pausing for a predetermined delay period when said received signal on said second channel terminates before 
     
     
        returning to said first channel. .Iaddend. .Iadd.29.  A system for monitoring one or more channels with minimal signal loss on received channels in a multichannel radio receiver, comprising: means for receiving a signal on a first channel;   means for detecting nulls in said received signal on said first channel; and   means for sampling a second channel for a received signal in response to detection of at least some of said nulls, thereby avoiding disruption in   
     
     
        said received signal on said first channel. .Iaddend. .Iadd.30.  The system of claim 29, including means for setting a minimum time period between samples of said second channel. .Iaddend. .Iadd.31. The system of claim 29, including means for setting a maximum time period between samples of said second channel. .Iaddend. .Iadd.32. The system of claim 29, including means for receiving only said received signal on said second channel when said received signal is detected during said sampling. .Iaddend. .Iadd.33. The system of claim 32, including means for returning to said first channel when said received signal on said second channel terminates. .Iaddend. .Iadd.34. The system of claim 33, including means for pausing for a predetermined delay period when said received signal on said second channel terminates before returning to said first channel. .Iaddend.