VOR RECEIVER WITH ADAPTIVE FILTERS AND PHASE SHIFTER FOR IMPROVED ACCURACY

• US 3,792,473 A
• Filed: 11/21/1972
• Issued: 02/12/1974
• Est. Priority Date: 11/21/1972
• Status: Expired due to Term

• Current Assignee: Joseph J. Sawicki
• Original Assignee: Joseph J. Sawicki
• Inventors: Sawicki, Joseph J.
• Primary Examiner(s): Wilbur, Maynard R.
• Assistant Examiner(s): Buczinski, S. C.
• Application Number:
  US05/308,393
• Time in Patent Office: 448 Days
• Field of Search: 343/16R 324/83R
• US Class Current: 342/401
• CPC Class Codes: G01S 1/02 using radio waves G01S19/00 takes precedence
• CPC Class Codes: H03H 11/1291 Current or voltage controlled filters

Abstract

An improved VOR receiver which includes adaptive band pass filters for the 30 Hz reference and variable signals and an electronic phase shifter for shifting the variable and reference signals into phase coincidence, the amount of phase shift thus introduced being a measure of VOR bearing angle. The phase shifter is controlled by a feedback loop having a limiter which controls the rate of change of phase shift as a function of distance from the VOR station thereby reducing effects of scolloping in the beam of the VOR transmitter upon bearing indications.

Claims

1. In a receiver for a VOR navigation system wherein bearing indicaTions are provided by comparing the phase of a reference signal and a variable signal received from a VOR transmitting station, the inprovement comprising, a voltage controlled phase shifter to which said reference signal and said variable signal is applied, said phase shifter including a clock oscillator having an output frequency substantially higher than the frequency of said reference and variable signals, said clock oscillator output frequency being variable as a function of a control voltage applied to said oscillator;

a frequency divider for said clock oscillator providing a first output signal substantially equal in frequency to the frequency of said variable signal, said divider also producing a second output in quadrature with said first output, a phase detector receiving said variable signal and said first and second outputs of said frequency divider for providing an error signal;

means for integrating said error signal and means for applying said integrated error signal to said clock oscillator to control the frequency thereof.

2. The improvement of claim 1 wherein said voltage controlled phase shift includes, a ramp generator providing an output of sawtooth waveform synchronized with said reference signal;

and, a sampling circuit, said sampling circuit being controlled by said divider to sample and hold a voltage from said ramp generator output corresponding to the difference in phase between said VOR reference and variable signals.

3. The improvement of claim 2 with additionally, a limiter interposed between said phase detector and said integrator for limiting the magnitude of said error signal.

4. An improved VOR receiver as claimed in claim 3 operating in conjunction with distance measuring equipment for determining the distance of said VOR receiver from the VOR transmitting station and with additionally, means for controlling as a function of the distance of said VOR receiver from the VOR transmitter the values to which the magnitude of said error signal is limited.

5. A receiver for a VOR navigation system in which bearing information is obtained by comparing phase of a variable signal with a reference signal, both signals being broadcast by a VOR transmitter, the phase between said signals being dependent upon the position of said receiver with respect to said transmitter, comprising a radio receiver including detector means for separating reference and variable signals transmitted by a VOR station;

a first adaptive filter for said reference signal;

a second adaptive filter for said variable signal;

each of said adaptive filters including an amplifier, a frequency selective network for said amplifier, said network including a voltage variable impedance, and means controlling said impedance including a detector for comparing quadrature phase relationship of the input signal to each said filter with the output signal therefrom;

means for determining the phase difference between output signals of said first and second adaptive filters; and

, means for indicating said phase difference.

6. A receiver as claimed in claim 5 wherein each said frequency selective network comprises an input branch through which signal is applied to said amplifier and an output branch through which output of said amplifier is fed back to the input thereof, said variable impedance forming a part of said output branch, and wherein said means controlling said impedance comprises means receiving output from said amplifier and producing a square wave therefrom, a detector receiving a signal simultaneously applied to said input branch of said network, said signal being either said reference signal or said variable signal, said detector being switched into and out of conduction by said square wave, and means providing the average value of signal conducted by said detector, said average value serving to control said variable impedance.

7. A receiver as claimed in claim 5 wherein said means for determining the phase difference includes a voltage controlled viable frequency clock oscillator having an output frequency substantially higher than the frequency of said VOR reference and variable signals, means for dividing the frequency of said clock oscillator substantially to the frequency of said VOR reference and variable signals;

and phase lock means receiving the output of said dividing means and one of said VOR signals, said phase lock means providing control voltage for said clock oscillator to cause output from said dividing means to maintain a fixed phase relationship with said one VOR signal received by said phase lock means.

8. A receiver as claimed in claim 7 wherein output of said dividing means constitutes two signals one of which is in phase with said one VOR signal received by said phase lock means and the other of which is in quadrature therewith and wherein said indicating means includes means for modulating the other of said VOR signals by said two signals from said dividing means to produce analog voltages of the sine and cosine functions of the bearing angle.

9. A receiver as claimed in claim 7 with additionally, second dividing means for further dividing the frequency of said clock oscillator to a sub-harmonic of the frequency of said VOR reference and variable signals, means receiving the output of said second dividing means and said VOR signal other than said one received by said phase lock means and providing a voltage related to said phase difference between said VOR reference and variable signals, said voltage exerting control on said clock oscillator in addition to said control voltage of said phase lock means.

10. A receiver as claimed in claim 8 with additionally phase shift means controlled manually to which said analog voltages are applied for shifting the phase of said analog voltages a preselected amount corresponding to a preselected bearing angle;

and, a phase detector receiving said phase shifted analog voltages from said manually controlled phase shifter and providing an output related to the difference between said preselected bearing angle and the VOR bearing angle.

11. A receiver as claimed in claim 10 with additionally;

means providing an analog voltage related to the distance of said receiver from said VOR transistor; and

multiplying means interposed between the output of said manually controlled phase shifter and said phase detector, said multiplying means supplying as input to said phase detector a voltage which is related to the product of said sine-cosine analog voltage and said distance analog voltage.

12. A receiver as claimed in claim 9 with additionally, a control gate receiving said VOR reference and variable signals and output from said clock oscillator, said gate being rendered conductive to transmit said clock oscillator output by one of said VOR signals and rendered non-conductive by the other of said VOR signals to block transmission of said clock oscillator output;

and, a counter receiving clock oscillator output transmitted by said control gate, said conductor accumulating a count of oscillations of said transmitted clock oscillator output to provide a digital representation of the VOR bearing angle.

13. A receiver for a VOR navigation system for vehicles wherein bearing indications are obtained in the receiver by comparing the phase of a variable signal with a reference signal both signals being broadcast as a composite signal by a VOR transmitter, comprising:

means for separating a received composite VOR signal into a variable signal and a reference signal;

an adaptive filter each for said variable signal and said reference signal. a voltage controlled phase shifter to which one of said filtered reference or variable signals is applied for shifting the phase of said one signal into coincidence with the other of said reference or variable signals;

a phase detector for comparing the phase of said other signal wIth output from said voltage controlled phase shifter to provide an error signal output;

an adjustable limiter to which said error signal output is applied for limiting the magnitude of said error signal to an adjusted maximum value;

means controlling said adjustment of said limiter as a function of the distance of said receiver from the VOR transmitter whereby said maximum value of said error signal is decreased at increased distances;

means for integrating said limited error signal to provide a control voltage for said voltage controlled phase shifter;

means for modulating output of said voltage controlled phase shifter by said one signal; and

, indicating means responsive to output from said modulating means for indicating VOR bearing data.

14. A VOR receiver as claimed in claim 13 wherein said indicating means includes a manually controlled phase shifter to which output from said modulating means is applied for shifting the phase thereof an amount corresponding to a selected VOR course;

multiplying means receiving output from said manually controlled phase shifter and data representative of the distance of said receiver from the VOR transmitter to provide an output proportional to the product of said distance and said manually controlled phase shifter output; and

, a null detector receiving said product from said multiplying means for indicating deviation of the vehicle carrying said receiver from said selected course.

15. A VOR receiver as claimed in claim 13 wherein said voltage controlled phase shifter comprises a ramp generator synchronized by said one signal to produce a sawtooth output waveform having a period which is an integral multiple of the period of said one signal;

a voltage controlled oscillator operating at a frequency substantially higher than that of said variable and reference signals;

means dividing the frequency of the output of said voltage controlled oscillator to the frequency of the output of said ramp generator;

means synchronized by output from said dividing means for sampling output from said ramp generator; and

, means applying output from said sampling means as a portion of the control voltage for said voltage controlled oscillator, the remainder of said oscillator control voltage being comprised of said integrator output.