Groundspeed measurement system
AssigneeUnited States of America
InventorForrest G. Yetter
Life of this patent
Estimating the term…
Abstract
A measurement system for determining the groundspeed of an aircraft during final approach and landing, by measuring at the aircraft the Doppler shift of a radio signal, and/or its modulation components, transmitted by a fixed ground station. The carrier signal is allowed to drift; it is provided with a modulated tone on the carrier having a frequency signature that identifies the direction and magnitude of this carrier frequency drift. In a second embodiment the Doppler cycles are not counted directly, but rather fixed increments of a cycle wavelength are measured; the time period of each segment is inverted to obtain a value proportional to the Doppler frequency.
Claims12
A method of measuring the motion of a receiving station relative to a transmitting station, comprising:
- generating electromagnetic energy in the radio frequency spectrum at the transmitting station;
- radiating said energy;
- detecting said energy at the receiving station;
- heterodyning said detected energy at said receiving station to generate a first reference frequency;
- synthesizing a second reference frequency at said receiving station which has a value equal to said first reference frequency when there is no relative motion between said transmitting station and said receiving station;
- mixing said first reference frequency with said second reference frequency to isolate a Doppler frequency;
- and
- processing said Doppler frequency to generate a signal having a value that is functionally related to said relative motion.
A method for measuring the motion of a receiving station relative to a transmitting station, comprising:
- generating electromagnetic energy in the radio frequency spectrum at the transmitting station;
- sampling a part of said energy;
- generating a first reference frequency;
- mixing said sampled energy and said first reference frequency to generate a difference frequency;
- modulating the energy output of said transmitting station with said difference frequency;
- detecting said modulated energy output at said receiving station;
- generating a second reference frequency at said receiving station;
- synthesizing at said receiving station additional frequencies from said second reference frequency;
- heterodyning said detected energy with said synthesized additional frequencies to produce a third reference frequency;
- demodulating said detected energy;
- mixing said demodulated energy with said reference frequency to produce a Doppler frequency;
- and
- processing said Doppler frequency to produce a signal having a value that is functionally related to said relative motion.
A method of measuring the motion of receiving station relative to transmitting station, comprising:
- generating electromagnetic energy in the radio frequency spectrum at the transmitting station;
- generating a modulation signal and applying said signal to said energy;
- radiating said electromagnetic energy with said modulation signal impressed thereon;
- detecting at the receiving station said energy radiated by said transmitting station;
- demodulating said detected energy;
- generating a reference frequency at a value having a known relation to the frequency of said modulation signal impressed on said energy radiated by said transmitting station;
- and
- mixing said demodulated signal with said reference signal to generate a Doppler signal having a parameter value that is functionally related to said relative motion.
A method of measuring the distance of a receiving station from a reference location comprising detecting a directional beam of electromagnetic energy radiated from a first ground station;
- generating pulses having a repetition frequency proportiponal to the range rate of said receiving station relative to a second ground station;
- counting said pulses for a finite period of time, initiating said counting action in response to the detection of said directional beam;
- and converting the quantity of pulses counted in said finite period of time to units of distance.
Dependencies are inferred from the claim text.