Automatic retransmission with pilot tone

• US 4,829,588 A
• Filed: 08/25/1981
• Issued: 05/09/1989
• Est. Priority Date: 08/25/1981
• Status: Expired due to Term

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Keyser, Dean
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US06/296,236
• Time in Patent Office: 2,814 Days
• Field of Search: 455/17, 455/20, 455/21, 455/25, 455/57, 455/9, 455/268, 455/58, 455/68, 455/70, 455/45, 455/228, 455/31, 455/35, 455/36, 370/53, 370/54, 370/75, 370/76, 307/3, 307/129, 307/358, 307/359, 340/825.03, 340/825.72, 340/291, 340/825.48, 340/825.74, 179/2.51, 179/170.4, 179/84 R, 179/84 T, 329/50, 329/110, 329/112
• US Class Current: 455/21
• CPC Class Codes: H04B 1/76 Pilot transmitters or receivers for control of transmission or for equalising

Abstract

A transceiver and method of controlling the automatic retransmission of a radio frequency commmunications signal in which a pilot tone within the radio frequency communications channel bandwidth but above the band of frequencies necessary for intelligence is phase modulated at a frequency below the frequency band of the intelligence and combined with the intelligence for transmission over a first frequency communication link. When received, the presence of the pilot tone and the modulation is detected, compared with predetermined standards and utilized to control the application of the demodulated intelligence to a second communication link. After establishing the second communication link, the predetermined standards utilized to control the application of the intelligence to the second communication link are relaxed.

Claims

1. A method of controlling the automatic retransmission of a radio frequency communication signal comprising the steps of:

(a) providing a pilot tone at a frequency within the radio frequency communication channel bandwidth but above the band of frequencies necessary for intelligence;

(b) phase modulating the pilot tone at a frequency below the intelligence;

(c) transmitting the radio frequency signal including the intelligence and the phase modulated pilot tone;

(d) receiving the radio frequency signal;

(e) detecting the presence of the pilot tone and the frequency of modulation thereof;

(f) comparing the detected frequency of modulation with a predetermined frequency standard with a predetermined accuracy standard;

(g) retransmitting the radio frequency signal responsively to the comparison; and

(h) modifying the accuracy standard of the frequency comparison responsively to the comparison.

2. A method of controlling the automatic retransmission of a high frequency radio communication signal comprising the steps of:

(a) providing a pilot tone at a frequency within the high frequency radio communication channel bandwidth but above the audio band of frequencies;

(b) phase modulating the pilot tone at a subaudible rate by means of a phase locked loop;

(c) providing an audio signal;

(d) summing the modulated pilot tone and the audio signal to form a modulation signal;

(e) transmitting a high frequency signal modulated by the modulation signal;

(f) receiving the high frequency signal;

(g) demodulating the high frequency signal to recover the modulation signal;

(h) removing the pilot tone and its modulation components from the recovered modulation signal by means of a notch filter;

(i) detecting the presence of the pilot tone and the subaudible rate by means of a phase locked loop;

(j) comparing to a predetermined accuracy standard the subaudible rate with a locally generated rate standard to provide a control signal;

(k) retransmitting the high frequency radio communication signal responsively to the control signal; and

(l) relaxing the predetermined accuracy standard or the rate comparison responsively to the control signal.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.