FM Radio ranging system
First Claim
1. A trilateralization position radar locating system having secondary user capabilities, said system comprising at least a master station and a stationary station, means for transmitting at least one linear and nonlimited radio ranging signal from said master station over a radio channel to said stationary station, said radio ranging signal having a predetermined repetition rate and a preprogrammed frequency change sweeping in one direction, means in said stationary station for identifying signals directed to it jointly responsive to an identification of the repetition rate and of said preprogrammed sweep of frequency, means at said stationary station responsive to the receipt of a signal identified by said repetition rate and by said preprogrammed sweep for transmitting at least one replying radio ranging signal from said stationary station to said master station with a predetermined repetition rate and with a preprogrammed frequency change sweeping in an opposite direction, and surface wave device means for causing said preprogrammed sweep of frequency change in said radio ranging signal responsive to a passage of an interrupted oscillatory signal through said device, said sweep frequency being free of superimposed modulating signals so that said transmitted signal is free of side bands, the frequency of said radio ranging signal sweeping past the frequency bands used by other and primary equipment fast enough to isolate primary and secondary user signals without causing any appreciable interference in said other and primary equipment.
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Abstract
A radio locator system uses transceivers located in a mobile and at least two stationary stations. Each stationary station serves as one end of a surveyor'"'"'s baseline. Therefore, since the transceivers are located at opposite ends of a line having a known length, their broadcast signals provide direct distance measurements of two other lines extending between the individual stationary stations and the mobile unit, thereby cooperating with the known line to complete a trilateralization. Each station in the system is identified by a uniquely encoded stream of pulse bursts, each burst encompassing a wide, preprogrammed change of frequency for eliminating interference between the signals used in the locator system and the signals of other users of the same frequency band. An inversion of the preprogrammed frequency change is used for the return of the ranging system signal in order to substantially eliminate or suppress echo returns to the mobile or interrogator station. The sound of the preprogrammed station identifying frequency changes is sometimes called "chirping".
40 Citations
19 Claims
- 1. A trilateralization position radar locating system having secondary user capabilities, said system comprising at least a master station and a stationary station, means for transmitting at least one linear and nonlimited radio ranging signal from said master station over a radio channel to said stationary station, said radio ranging signal having a predetermined repetition rate and a preprogrammed frequency change sweeping in one direction, means in said stationary station for identifying signals directed to it jointly responsive to an identification of the repetition rate and of said preprogrammed sweep of frequency, means at said stationary station responsive to the receipt of a signal identified by said repetition rate and by said preprogrammed sweep for transmitting at least one replying radio ranging signal from said stationary station to said master station with a predetermined repetition rate and with a preprogrammed frequency change sweeping in an opposite direction, and surface wave device means for causing said preprogrammed sweep of frequency change in said radio ranging signal responsive to a passage of an interrupted oscillatory signal through said device, said sweep frequency being free of superimposed modulating signals so that said transmitted signal is free of side bands, the frequency of said radio ranging signal sweeping past the frequency bands used by other and primary equipment fast enough to isolate primary and secondary user signals without causing any appreciable interference in said other and primary equipment.
- 8. A secondary use of a radio frequency spectrum pulse signalling system having echo suppression, said system comprising a station having a send channel and a receive channel using the same wide frequency band, remote transponder means for receiving pulse signals on the send channel and reflectively returning the same pulse signals on the receive channel, means including a surface wave device for sweeping said pulse signal with a high speed preprogrammed shift of frequency to provide a chirp signal which sweeps past primary user bands fast enough to provide isolation with virtually no noise factor, and means for causing said sweep to move toward higher frequencies in one of said channels and toward lower frequencies on the other of said channels so that one channel signals with up-chirping and the other channel signals with down-chirping, whereby said station can distinguish between the signals which it sends and the reflection of those signals which the transponder returns.
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12. A method of signal channel frequency allocation comprising the steps of:
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(a) assigning a predetermined frequency band to a primary user having receivers with band pass filters tuned to pass said frequency band; (b) assigning said predetermined frequency band to secondary users having send and receive signal channels also tuned to said band; (c) transmitting preprogrammed signals over said secondary users signal channels in said predetermined frequency band; and (d) sweeping the frequency in said secondary users signal system past the band of said primary users signals at a rapid rate to preclude an interference. - View Dependent Claims (13, 14)
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- 15. A secondary user radar system using chirp signalling comprising a plurality of stations, each of said stations being identified by cyclically recurring bursts of unmodulated radio frequency signals which are free of side bands, said bursts recurring with a burst repetition rate individually assigned to identify each of said stations, means for transmitting signals from one of said stations to a transponder station which reflectively returns the same modulated signal to the transmitting station, means in said transmitting station for changing said radio frequency in a preprogrammed manner to produce a chirp signal during each burst of radio frequency, and means in said transponder station for reflectively returning said same signal to said station while precluding intersignal interference by using a different preprogrammed frequency change to produce a different form of chirp signal, the frequency changes sweeping by the assigned pass bands of primary users of the same frequencies within a time period which is short enough to produce a high level of isolation between signals of said primary and secondary users.
Specification