Automatic retransmission with pilot tone

Claim 5

In a method of obtaining a desired degree of selectivity in an audio frequency communication system by recognition of information signals at two discrete frequencies wherein the signal having the higher frequency is modulated by the signal having the lower frequency so that the lower frequency is accurately recoverable despite variations in the high frequency within the tolerance of audio frequency communication systems, the improvement wherein the accuracy of recognition of the lower frequency is reduced once the lower frequency is detected.

Claim 6

In a method of obtaining a desired degree of selectivity in an audio frequency communication system by recognition of information signals at two discrete frequencies wherein the signal having the higher frequency is modulated by the signal having the lower frequency so that the lower frequency is accurately recoverable despite variations in the high frequency within the tolerance of audio frequency communication systems, the improvement wherein the accuracy of recognition of the lower frequency is reduced once the lower frequency is detected.

Claim 7

In a radio frequency communication system having a predetermined channel bandwidth including a spectrum of bandwidth necessary for voice communication, a method of detecting a relatively low frequency signal comprising the steps of: (a) providing a relatively high frequency signal within the channel bandwidth, the relatively high frequency signal being above the spectrum of bandwidth in the channel necessary for voice communication; (b) phase modulating the relatively high frequency signal by a relatively low frequency signal below the spectrum of bandwidth in the channel necessary for voice communication; (c) providing a voice communication signal; (d) filtering the voice communication signal to clear space for the phase modulated relatively high frequency signal; (e) superimposing the phase modulated relatively high frequency signal on the voice communication signal; (f) transmitting the superimposed signals; (g) receiving the superimposed signals; (h) removing the voice communication signal from the superimposing signal by a high pass filter; (i) demodulating the phase modulated relatively high frequency signal to recover the relatively low frequency signal to an accuracy variable as a function of prior recovery of the relatively low frequency signal; and (j) removing the relatively high frequency signal from the voice communication signal by a notch filter.

Claim 8

In a radio frequency communication system having a predetermined channel bandwidth including a spectrum of bandwidth necessary for voice communication, a method of detecting a relatively low frequency signal comprising the steps of: (a) providing a relatively high frequency signal within the channel bandwidth, the relatively high frequency signal being above the spectrum of bandwidth in the channel necessary for voice communication; (b) phase modulating the relatively high frequency signal by a relatively low frequency signal below the spectrum of bandwidth in the channel necessary for voice communication; (c) providing a voice communication signal; (d) filtering the voice communication signal to clear space for the phase modulated relatively high frequency signal; (e) superimposing the phase modulated relatively high frequency signal on the voice communication signal; (f) transmitting the superimposed signals; (g) receiving the superimposed signals; (h) removing the voice communication signal from the superimposing signal by a high pass filter; (i) demodulating the phase modulated relatively high frequency signal to recover the relatively low frequency signal to an accuracy variable as a function of prior recovery of the relatively low frequency signal; and (j) removing the relatively high frequency signal from the voice communication signal by a notch filter.

Claim 9

The method of claim 4 wherein the initial degree of accuracy is about three percent; wherein the voice communication signal is between about 300 Hz and about 2000 Hz; wherein the relatively low frequency signal is between about 30 Hz and about 70 Hz; wherein the voice communication signal is filtered to remove frequencies below about 2000 Hz; and wherein the notch filter is approximately 200 Hz wide with sidebands at 40 db rejection.

Claim 10

An automatic retransmission radio frequency communication system comprising: means for generating a pilot tone at a frequency within the radio frequency communication channel bandwidth but above the band of frequencies necessary for intelligence; means for phase modulating said pilot tone at a frequency below the intelligence; means for transmitting a radio frequency signal including the intelligence and the phase modulated pilot tone; means remote from said transmitting means for receiving the transmitted radio frequency signal; means for detecting the presence of the pilot tone and the frequency of modulation thereof; means having a first accuracy requirement for comparing the detected frequency of modulation with a predetermined standard until a predetermined condition is met and thereafter having a second accuracy requirement less than said first accuracy requirement; and means responsive to said comparison means for retransmitting the radio frequency signal.

Claim 11

An automatic retransmission radio frequency communication system comprising: means for generating a pilot tone at a frequency within the radio frequency communication channel bandwidth but above the band of frequencies necessary for intelligence; means for phase modulating said pilot tone at a frequency below the intelligence; means for transmitting a radio frequency signal including the intelligence and the phase modulated pilot tone; means remote from said transmitting means for receiving the transmitted radio frequency signal; means for detecting the presence of the pilot tone and the frequency of modulation thereof; means having a first accuracy requirement for comparing the detected frequency of modulation with a predetermined standard until a predetermined condition is met and thereafter having a second accuracy requirement less than said first accuracy requirement; and means responsive to said comparison means for retransmitting the radio frequency signal.

Claim 12

An automatic retransmission high frequency radio communication system comprising: means for providing a pilot tone at a frequency within the high frequency radio communication channel bandwidth but above the audio band of frequencies; means for phase modulating said pilot tone at a subaudible rate by means of a phase locked loop; means for providing an audio signal; means for superimposing said modulated pilot tone of said audio signal to form a modulation signal; means for transmitting a high frequency signal modulated by said modulation signal; means for receiving said high frequency signal; means for demodulating said high frequency signal to recover the modulation signal; notch filter means for removing said pilot tone and its modulation components from said modulation signal; phase locked loop means for detecting the presence of said pilot tone and said subaudible rate; means for comparing said subaudible rate with a locally generated rate standard to provide a control signal; means responsive to said control signal for retransmitting said high frequency radio communication signal; and means responsive to said control signal for modifying the accuracy requirements of said comparing means.

Claim 13

An automatic retransmission high frequency radio communication system comprising: means for providing a pilot tone at a frequency within the high frequency radio communication channel bandwidth but above the audio band of frequencies; means for phase modulating said pilot tone at a subaudible rate by means of a phase locked loop; means for providing an audio signal; means for superimposing said modulated pilot tone of said audio signal to form a modulation signal; means for transmitting a high frequency signal modulated by said modulation signal; means for receiving said high frequency signal; means for demodulating said high frequency signal to recover the modulation signal; notch filter means for removing said pilot tone and its modulation components from said modulation signal; phase locked loop means for detecting the presence of said pilot tone and said subaudible rate; means for comparing said subaudible rate with a locally generated rate standard to provide a control signal; means responsive to said control signal for retransmitting said high frequency radio communication signal; and means responsive to said control signal for modifying the accuracy requirements of said comparing means.