Signal generator for testing vor navigation receivers

Claim 2

A signal generator for testing a VOR receiver which receiver provides bearing information by comparing the phase of a variable signal with a reference signal, said reference and variable signals being transmitted to said receiver as a composite signal simultaneously frequency and amplitude modulated, comprising a stable oscillator operating at a frequency which is a high order harmonic of the frequency of said reference signal; digital means for dividing in multiple stages the frequency of said stable oscillator to the frequency of said reference signal; presettable logic means for detecting accumulation of count by said dividing means corresponding to a selected phase angle between said reference and variable signals; register means triggered by said logic means and settable upon receipt of trigger from said logic means to the relative polarity at the instant of triggering of the output of said dividing means; a subcarrier generator providing an output having a frequency substantially higher than the frequency of said reference signal; means for modulating the frequency of subcarrier output from said subcarrier generator by output from said dividing means; means for modulating the amplitude of said frequency modulated subcarrier output by output from said register means to provide a composite signal; and means for applying said composite signal to the VOR receiver to be tested.

Claim 3

A signal generator as claimed in claim 1 wherein the outputs of said dividing means and said register means are of square waveform and with additionally, means for converting output of said dividing means into sine waveform for modulating the frequency of said subcarrier; and means for converting the output of said register means to sine waveform for modulating the amplitude of said frequency modulated subcarrier.

Claim 4

A signal generator as claimed in claim 1 wherein said subcarrier generator and means for modulating the frequency thereof comprises the combination of a voltage controlled oscillator operating at the frequency of said subcarrier output; second dividing means for dividing the frequency of output of said voltage controlled oscillator by a fixed number substantially to the frequency of output of said first named diViding means; means for comparing the phase of output from said second dividing means with output from said first named dividing means; and means for combining output from said phase comparing means with output from said first named dividing means to provide control voltage for said voltage controlled oscillator.

Claim 5

A signal generator as claimed in claim 3, with additionally, means for measuring the deviation ratio of said frequency modulated subcarrier output, including means for comparing the time duration of a fractional part of one cycle of output from said second dividing means with the time duration of a similar fractional part of one cycle of output from said first named dividing means.

Claim 6

A signal generator as claimed in claim 1, with additionally, means receiving said composite signal and recovering therefrom the information signal conveyed by the frequency modulation thereof and the information conveyed by the amplitude modulation thereof; means for comparing the phase of said information signal recovered from frequency modulation with the output of said dividing means to provide a first phase error output; means for comparing the phase of said information signal recovered from amplitude modulation with the output of said register means to provide a second phase error output; and means for combining said first and second phase error outputs to provide a total phase error output.

Claim 7

A signal generator as claimed in claim 5, with additionally, a voltage controlled phase shifter for shifting the phase of output from said register means prior to the utilization of said register output in said means for modulating amplitude, said phase shifter receiving said total phase error output as control voltage.

Claim 8

A signal generator for testing a VOR receiver which receiver provides bearing information by comparing the phase of variable signal with a reference signal, said reference and variable signals being transmitted to said receiver as a composite signal simultaneously frequency and amplitude modulated, comprising, a stable oscillator operating at a frequency which is a high order harmonic of the frequency of said reference signal; digital means for dividing in successive stages the frequency of said stable oscillator output to provide an output corresponding to said reference signal; a phase selector switch settable to an angle at which the bearing angle indicated by said receiver is to be tested, said switch providing an output which is the binary coded decimal of the phase angle set thereon; logic circuits connected between said switch and stages of said dividing means with the least significant digit of output from said switch controlling the logic circuit connected to a stage of said dividing means nearest the input thereto from said stable oscillator and outputs from said switch representing more significant digits of selected phase angle being connected to successive stages of said dividing means in ascending order of significance; register means controlled by said logic circuits, saud register means having a capacity of a single bit of said reference signal output from said dividing means and providing an output corresponding to said variable signal, said register being cycled by said logic means upon accumulation of count by said dividing means equivalent to the phase angle selected on said switch; a subcarrier generator providing an output having a frequency substantially higher than said reference frequency output; means for frequency modulating said subcarrier output by said reference frequency output; means for modulating the amplitude of said frequency modulated subcarrier by said variable signal output of said register means to provide a composite signal; and means for applying said composite signal to the VOR receiver to be tested.

Claim 9

A signal generator for testing a VOR receiver which receiver provides bearing information by comparing the phase of variable signal with a reference signal, said reference and variable signals being transmitted to said receiver as a composite signal simultaneously frequency and amplitude modulated, comprising, a stable oscillator operating at a frequency which is a high order harmonic of the frequency of said reference signal; digital means for dividing in successive stages the frequency of said stable oscillator output to provide an output corresponding to said reference signal; a phase selector switch settable to an angle at which the bearing angle indicated by said receiver is to be tested, said switch providing an output which is the binary coded decimal of the phase angle set thereon; logic circuits connected between said switch and stages of said dividing means with the least significant digit of output from said switch controlling the logic circuit connected to a stage of said dividing means nearest the input thereto from said stable oscillator and outputs from said switch representing more significant digits of selected phase angle being connected to successive stages of said dividing means in ascending order of significance; register means controlled by said logic circuits, saud register means having a capacity of a single bit of said reference signal output from said dividing means and providing an output corresponding to said variable signal, said register being cycled by said logic means upon accumulation of count by said dividing means equivalent to the phase angle selected on said switch; a subcarrier generator providing an output having a frequency substantially higher than said reference frequency output; means for frequency modulating said subcarrier output by said reference frequency output; means for modulating the amplitude of said frequency modulated subcarrier by said variable signal output of said register means to provide a composite signal; and means for applying said composite signal to the VOR receiver to be tested.

Claim 10

A signal generator as claimed in claim 7 wherein said logic means are arranged to cycle said register means after accumulatioN of count by said dividing means corresponding to the phase angle selected on said switch when the selected angle is less than 180* and is arranged to cycle said register after accumulation of count by said dividing means corresponding to the difference between the selected angle and 180* when the selected angle is 180* or greater.

Claim 11

A signal generator as claimed in claim 8 wherein said logic means control said register to produce an output of the same polarity as said reference signal output from said dividing means when the selected angle is less than 180* and to produce an output of opposite polarity to said reference signal output when the selected angle is 180* or greater.

Claim 12

A signal generator as claimed in claim 7 wherein said subcarrier generator and means for modulating the frequency thereof comprises a voltage controlled oscillator operating at the frequency of said subcarrier output; second dividing means for dividing the frequency of output of said voltage controlled oscillator by a fixed number substantially to the frequency of said reference signal output from said first named dividing means, means for comparing the phase of output from said second dividing means with said reference signal output; means for integrating with respect to time the output from said phase comparing means; means providing a fixed bias output; and means for combining said reference signal output, said fixed bias output and output of said integrating means to provide control voltage for said voltage controlled oscillator.

Claim 13

A signal generator as claimed in claim 10 with additionally means for measuring the deviation ratio of said frequency modulated subcarrier output, including a pulsewidth subtractor providing an output related to the difference between the periods of one-half cycle of output from said second dividing means and one-half cycle of said reference signal output; a clock oscillator; means controlled by said pulsewidth subtractor for storing pulses from said clock oscillator; and means for indicating the number of said clock pulses contained by said storing means.

Claim 14

A signal generator as claimed in claim 7, with additionally, means for determining phase error in said composite signal, including means receiving said composite signal and demodulating the same to provide recovered reference and variable signals; means for comparing the phase of said recovered reference signal with said reference signal output to provide a first phase error signal; means for comparing the phase of said recovered variable signal with said variable signal output to provide a second phase error signal; means for combining said first and second phase error signals to provide a total phase error signal; and means for quantitatively indicating said total phase error signal.

Claim 15

A signal generator as claimed in claim 12 with additionally a voltage controlled phase shifter effective to shift the phase relationship between said reference signal output and said variable signal output prior to utilization of said reference and variable signal outputs in said frequency and amplitude modulation means; and means applying said total phase error signal as control voltage to said phase shifter to cause said phase shifter to reduce the total phase error.