Navigation aid transmitter-monitor system

Claim 2

A monitor system for a radio navigation aid transmitter of the kind which transmits radio signals in a pattern defining a course plane in space, said monitor system including at least three separate monitor receiver antennas arranged at different displacement positions in space with respect to the course plane to monitor the signal pattern at each of said positions, a plurality of monitor receiver channels equal in number to the number of said monitor receiver antennas, a separate one of said monitor receiver channels being connected to each of said monitor receiver antennas for separately determining for each monitor receiver antenna the presence of deviations of the received signals from values within predetermined limits allowable for the portion of the radio signal pattern monitored by that antenna, a signal reference level circuit for providing reference level signals for defining said predetermined limits for said received signals for all of said monitor receiver channels, said signal reference level circuit being connected to one of said monitor receiver channels and being operable to receive a signal from said last-mentioned monitor receiver channel proportional to the strength of the carrier signal received bY that channel and operable to generate said reference level signals proportionally to said carrier signal.

Claim 3

A system as defined in claim 1 wherein said signal reference level circuit comprises an amplifying means connected to said one of said monitor receiver channels, said amplifying means being operable to amplify the detected carrier envelope to derive a D.C. voltage proportional to the carrier envelope as a power level voltage signal, a voltage dividing means connected to receive said power level voltage signal and operable to select a fraction of said power level voltage signal as a power level error limit voltage, means connected to add said power level error limit voltage to said power level voltage signal to derive a voltage sum to be used to provide an upper signal reference level voltage, and means for subtracting said power level error limit voltage from said power level voltage signal to derive a difference voltage to thereby provide a lower signal reference level voltage.

Claim 4

A system as claimed in claim 2 wherein said voltage dividing means is adjustable to provide an adjustment of the ratio of said power level error limit voltage to said power level voltage signal to thereby symmetrically adjust said upper signal reference level and said lower signal reference level voltages about the voltage value of said power level voltage signal to provide wider or narrower spreads between said upper and said lower signal reference voltage levels.

Claim 5

A monitor system as claimed in claim 1 wherein said signal reference level circuit comprises an amplifying means connected to said one of said monitor receiver channels, said amplifying means being operable to amplify the detected carrier envelope to derive a D.C. voltage proportional to the carrier envelope as a power level voltage signal, a calibrated standard D.C. voltage source, and means for comparing said power level voltage signal with the output of said standard D.C. voltage source to determine the existence of a low power level in said one of said monitor receiver channels.

Claim 6

A monitor system as claimed in claim 1 wherein there is provided a common shut-down control means connected to all of said monitor receiver channels and operable in response to a deviation of the signal from any one of said channels from values within said predetermined limits to shut down the transmitter.

Claim 7

A monitor system for a radio navigation aid transmitter of the kind which transmits radio signals in a pattern defining a course plane in space, said monitor system including a plurality of separate monitor receiver antennas arranged at different displacement positions in space with respect to the course plane to monitor the signal pattern at each of said positions, a plurality of monitor receiver channels equal in number to the number of said monitor receiver antennas, a separate one of said monitor receiver channels being connected to each of said monitor receiver antennas for separately determining for each monitor receiver antenna the presence of deviations of the received signals from values within predetermined limits, a common shut-down control means connected to all of said monitor receiver channels and operable in response to a deviation of the signal from any of said channels from values within said predetermined limits to shut down the transmitter, a separate persistence circuit means connected from each monitor receiver channel to said common shut-down control means, each persistence circuit means being operable to cause the delivery of a deviation signal from the associated channel to said shut-down control means only after the deviation signal has persisted for a period long enough to be indicative of a serious continuing malfunction rather than a harmless transient condition.

Claim 8

A monitor system for a radio navigation aid transmitter of the kind which transmits radio signals in a pattern defining a course plane in space, said monitor system including a plurality of separate monitor receiver antennas arranged at different displacement positions in space with respect to the course plane to monitor the signal pattern at each of said positions, a plurality of monitor receiver channels equal in number to the number of said monitor receiver antennas, a separate one of said monitor receiver channels being connected to each of said monitor receiver antennas for separately determining for each monitor receiver antenna the presence of deviations of the received signals from values within predetermined limits, a common shut-down control means connected to all of said monitor receiver channels and operable in response to a deviation of the signal from any of said channels from values within said predetermined limits to shut down the transmitter, a separate persistence circuit means connected from each monitor receiver channel to said common shut-down control means, each persistence circuit means being operable to cause the delivery of a deviation signal from the associated channel to said shut-down control means only after the deviation signal has persisted for a period long enough to be indicative of a serious continuing malfunction rather than a harmless transient condition.

Claim 9

A system as claimed in claim 6 wherein each of said persistence circuit means comprises a digital counter which is operable to issue a shut-Down control signal to said shut-down control means upon the achievement of a predetermined count value, said counter being enabled to commence counting upon the initiation of a deviation signal from the associated channel and to continue counting as long as said deviation signal persists, and means for periodically resetting all of said digital counters.

Claim 10

A system as claimed in claim 7 wherein said means for periodically resetting all of said digital counters comprises a separate reference digital counter operable to continuously repeat a counting cycle and to emit a reset signal to all of the others of said digital counters whenever a particular count value is achieved in said reference counter, the complete cycle period of operation of said reference counter being longer than the individual periods of operation of said digital counters from reset to said predetermined value when continuously enabled.

Claim 11

A monitor system for a radio navigation aid transmitter of the kind which transmits radio signals in a pattern defining a course plane in space, said monitor system including at least three separate monitor receiver antennas arranged at different displacement positions in space with respect to the course plane to monitor the signal pattern at each of said positions, a plurality of monitor receiver channels equal in number to the number of said monitor receiver antennas, a separate one of said monitor receiver channels being connected to each of said monitor receiver antennas for separately determining for each monitor receiver antenna the presence of deviations of the received signals from values within predetermined limits, said monitor receiver antennas being positioned at distances from the navigation aid transmitter antennas sufficient to receive and sample the fully defined radiation pattern to be received by the receivers of vehicles using said radio signals, said system including a switched scanning beam radio navigation aid transmitter to be monitored, said radio navigation aid transmitter including a plurality of individual antenna elements combined in an array, said transmitter being operable to switch the signal radiations in sequence to all of said transmitter antenna elements in rapid succession to thereby set up a switched scanning beam radiation pattern comprised of sequentially switched individual radiation beams from each transmitter antenna element, the radiation beams being modulated with two different navigation signal tones, the mix of navigation tone signals being different on the beams from different transmitter antenna elements, said different displacement positions of said monitor receiver antennas comprising positions angularly spaced between adjacent transmitter antenna elements so that each of said monitor receiver antennas is in a position to respond primarily to the two adjacent beams from said adjacent transmitter antenna elements to detect variations in the balance of the signals contributed by the respective adjacent beams.

Claim 12

A monitor system for a radio navigation aid transmitter of the kind which transmits radio signals in a pattern defining a course plane in space, said monitor system including at least three separate monitor receiver antennas arranged at different displacement positions in space with respect to the course plane to monitor the signal pattern at each of said positions, a plurality of monitor receiver channels equal in number to the number of said monitor receiver antennas, a separate one of said monitor receiver channels being connected to each of said monitor receiver antennas for separately determining for each monitor receiver antenna the presence of deviations of the received signals from values within predetermined limits, said monitor receiver antennas being positioned at distances from the navigation aid transmitter antennas sufficient to receive and sample the fully defined radiation pattern to be received by the receivers of vehicles using said radio signals, said system including a switched scanning beam radio navigation aid transmitter to be monitored, said radio navigation aid transmitter including a plurality of individual antenna elements combined in an array, said transmitter being operable to switch the signal radiations in sequence to all of said transmitter antenna elements in rapid succession to thereby set up a switched scanning beam radiation pattern comprised of sequentially switched individual radiation beams from each transmitter antenna element, the radiation beams being modulated with two different navigation signal tones, the mix of navigation tone signals being different on the beams from different transmitter antenna elements, said different displacement positions of said monitor receiver antennas comprising positions angularly spaced between adjacent transmitter antenna elements so that each of said monitor receiver antennas is in a position to respond primarily to the two adjacent beams from said adjacent transmitter antenna elements to detect variations in the balance of the signals contributed by the respective adjacent beams.

Claim 13

A system as claimed in claim 1 wherein said system includes the radio navigation aid transmitter to be monitored, said transmitter including means for transmitting a standard radio frequency within the same frequency band with the transmitter signal carrier frequency and having a predetermined difference frequency from the carrier frequency, a connection from said navigation aid transmitter for carrying the standard radio frequency to said monitor receiver channels, each of said monitor receiver channels including a mixer connected to receive said standard radio frequency and operable to convert the modulated carrier frequency signal in said receiver channel to a difference frequency signal consisting of the difference between the carrier frequency signal and the standard frequency.

Claim 14

A system as claimed in claim 10 wherein the standard frequency is transmitted from said transmitter to said monitor receiver channels in The form of a frequency which is a predetermined fraction of said standard frequency to prevent high frequency energy losses, said monitor including a frequency multiplier to raise the frequency of the transmitted fractional frequency to the full standard frequency value.

Claim 15

A system as claimed in claim 1 wherein separate switching means are provided in each monitor receiver channel, said switching means being operable to switch synthesized deviation signals into said monitor receiver channels to check the integrity of said monitor receiver channels by determining whether or not said channels are operable for determining the presence of deviations from values within said predetermined limits.

Claim 16

A monitor system as claimed in claim 1 wherein the radio navigation aid signals transmitted by the navigation aid transmitter to be monitored to define the course plane in space comprise carrier signals modulated with different predetermined mixtures of two navigation signal tones at different positions with respect to said course plane, each of said monitor receiver channels being operable to determine whether or not the correct mixture of modulation tones exists in the signals received by the antenna associated with said monitor channel.

Claim 17

A monitor system for a radio navigation aid transmitter of the kind which transmits radio signals in a pattern defining a course plane in space, said monitor system including a plurality of separate monitor receiver antennas arranged at different displacement positions in space with respect to the course plane to monitor the signal pattern at each of said positions, a plurality of monitor receiver channels equal in number to the number of said monitor receiver antennas, a separate one of said monitor receiver channels being connected to each of said monitor receiver antennas for separately determining for each monitor receiver antenna the presence of deviations of the received signals from values within predetermined limits, the radio navigation aid signals transmitted by the navigation aid transmitter to be monitored to define the course plane in space comprising carrier signals modulated with different predetermined mixtures of two navigation signal tones at different positions with respect to said course plane, each of said monitor receiver channels being operable to determine whether or not the correct mixture of modulation tones exists in the signals received by the antenna associated with said monitor channel, said system including a radio navigation aid transmitter to be monitored, separate detector gating devices being provided for respectively detecting the presence of said separate modulation signal tones within each channel, connections from said transmitter to said detector gating devices for carrying said respective modulation tone signals from said transmitter to said gating devices, said gating devices being operable to gate on and off in synchronism with the individual cycles of said tone signals received from said transmitter to detect the depth of modulation of each of said tones in the radio carrier signals received by the associated monitor channel.

Claim 18

A monitor system for a radio navigation aid transmitter of the kind which transmits radio signals in a pattern defining a course plane in space, said monitor system including a plurality of separate monitor receiver antennas arranged at different displacement positions in space with respect to the course plane to monitor the signal pattern at each of said positions, a plurality of monitor receiver channels equal in number to the number of said monitor receiver antennas, a separate one of said monitor receiver channels being connected to each of said monitor receiver antennas for separately determining for each monitor receiver antenna the presence of deviations of the received signals from values within predetermined limits, the radio navigation aid signals transmitted by the navigation aid transmitter to be monitored to define the course plane in space comprising carrier signals modulated with different predetermined mixtures of two navigation signal tones at different positions with respect to said course plane, each of said monitor receiver channels being operable to determine whether or not the correct mixture of modulation tones exists in the signals received by the antenna associated with said monitor channel, said system including a radio navigation aid transmitter to be monitored, separate detector gating devices being provided for respectively detecting the presence of said separate modulation signal tones within each channel, connections from said transmitter to said detector gating devices for carrying said respective modulation tone signals from said transmitter to said gating devices, said gating devices being operable to gate on and off in synchronism with the individual cycles of said tone signals received from said transmitter to detect the depth of modulation of each of said tones in the radio carrier signals received by the associated monitor channel.

Claim 19

A system as claimed in claim 14 wherein said gating devices for detecting the depth of modulation of said two tone signals within each channel are connected to a common output, and means for reversing the phase of said tone gating signals from said transmitter for one of said tones supplied to one of said gating devices for each channel so that the d.c. component of the output signal from one of said gating devices is opposite in polarity to the d.c. component of the output from the other one of said gating devices for subtraction therefrom, and means for detecting the difference in said d.c. components of said detected depth of modulation signals to directly provide a difference in depth of modulation signal.

Claim 20

The combination of a radio navigation aid transmitter of the kind which tranSmits radio signals in a pattern defining a course plane in space and a monitor system for said transmitter, said monitor system including a plurality of separate monitor receiver antennas arranged at different displacement positions in space with respect to the course plane to monitor the signal pattern at each of said positions, a plurality of monitor receiver channels equal in number to the number of said monitor receiver antennas, a separate one of said monitor receiver channels being connected to each of said monitor receiver antennas for separately determining for each monitor receiver antenna the presence of deviations of the received signals from values within predetermined limits, said radio navigation aid transmitter including means for providing an identity code signal in the form of a predetermined signal tone which is modulated upon the radio navigation aid carrier signals in an interrupted Morse code pattern identifying the station from which the signals are transmitted, said system including an identity code monitor comprising an identity code generator operable to generate Morse code signals corresponding to the identification Morse code signals carried by said identity code signal tone modulation, and means associated with one of said monitor receiver channels for detecting the presence of identity code tone modulation and for comparing the resultant Morse code identity signals received from said transmitter with the identity code signals from said monitor identity code generator to conform the correctness of the identity code signals transmitted by said transmitter.

Claim 21

The combination of a radio navigation aid transmitter of the kind which tranSmits radio signals in a pattern defining a course plane in space and a monitor system for said transmitter, said monitor system including a plurality of separate monitor receiver antennas arranged at different displacement positions in space with respect to the course plane to monitor the signal pattern at each of said positions, a plurality of monitor receiver channels equal in number to the number of said monitor receiver antennas, a separate one of said monitor receiver channels being connected to each of said monitor receiver antennas for separately determining for each monitor receiver antenna the presence of deviations of the received signals from values within predetermined limits, said radio navigation aid transmitter including means for providing an identity code signal in the form of a predetermined signal tone which is modulated upon the radio navigation aid carrier signals in an interrupted Morse code pattern identifying the station from which the signals are transmitted, said system including an identity code monitor comprising an identity code generator operable to generate Morse code signals corresponding to the identification Morse code signals carried by said identity code signal tone modulation, and means associated with one of said monitor receiver channels for detecting the presence of identity code tone modulation and for comparing the resultant Morse code identity signals received from said transmitter with the identity code signals from said monitor identity code generator to conform the correctness of the identity code signals transmitted by said transmitter.

Claim 22

A monitor system for a radio navigation aid transmitter of the kind which transmits radio signals in a pattern defining a course plane in space, said monitor system including a plurality of separate monitor receiver antennas arranged at different displacement positions in space with respect to the course plane to monitor the signal pattern at each of said positions, a plurality of monitor receiver channels equal in number to the number of said monitor receiver antennas, a separate one of said monitor receiver channels being connected to each of said monitor receiver antennas for separately determining for each monitor receiver antenna the presence of deviations of the received signals from values within predetermined limits, means connected to a first one of said monitor receiver channels for measuring the power level of the carrier signal received by said first receiver channel, means for measuring the power level of a signal received in a second one of said monitor receiver channels, and means for comparing the carrier power level measurement from said power level measuring means for said first channel with said power level signal from said second channel to detect any deviations beyond predetermined limits in the relative power levels from said channels.

Claim 23

A monitor system for a radio navigation aid transmitter of the kind which transmits radio signals in a pattern defining a course plane in space, said monitor system including a plurality of separate monitor receiver antennas arranged at different displacement positions in space with respect to the course plane to monitor the signal pattern at each of said positions, a plurality of monitor receiver channels equal in number to the number of said monitor receiver antennas, a separate one of said monitor receiver channels being connected to each of said monitor receiver antennas for separately determining for each monitor receiver antenna the presence of deviations of the received signals from values within predetermined limits, means connected to a first one of said monitor receiver channels for measuring the power level of the carrier signal received by said first receiver channel, means for measuring the power level of a signal received in a second one of said monitor receiver channels, and means for comparing the carrier power level measurement from said power level measuring means for said first channel with said power level signal from said second channel to detect any deviations beyond predetermined limits in the relative power levels from said channels.

Claim 24

A system as claimed in claim 17 wherein the signal received in said second channel which is measured by said second channel power level measuring means comprises a detected modulation signal, said comparing means being operable to determine whether or not the depth of modulation indicated by said detected modulation signal is within predetermined limits while at the same time accomplishing a comparison in power levels in said first and second channels.

Claim 25

A system as claimed in claim 18 wherein said first channel comprises the center channel of the monitor system which is arranged to monitor the signals at the course plane in space, said system including a plurality of additional monitor receiver antennas and separate monitor receiver channels respectively associated therewith, a comparison means associated with each of said monitor receiver channels and operable to compare depth of modulation signals in each of said channels with power level signals from said center channel to accomplish a combined monitoring of the depth of modulation in each Channel and monitoring of the power level in each channel with relation to the power level of the center channel.