Passive ranging system utilizing range tone signals

A passive ranging system for determining the straight-line distance between first and second points, comprising, in combination:

• a radio transmitter at the first point for transmitting constant frequency range tones received from remote radio beacons at diverse geographical locations of known finite distances from the second point, each of the range tones being unique for respective ones of said beacons;
• first receiver means at the second point for detecting the range tones from said transmitter;
• second receiver means at said second point for detecting the range tones by a wireless link directly from the radio beacons;
• selector means coupled to said first and second receiver means for passing the range tones unique to one of said beacons;
• comparator means coupled to said selector means for measuring the phase difference between the range tones from said selector means;
• and
• computer means coupled to said comparator means responsive to (a) the phase comparison, (b) the distance between said second point and the beacon associated with the selected range tones, and (c) the direction from said second point to said first point, for determining the straight-line distance between said first and second points.

A passive ranging system for a drifting radiosonde utilizing remote radio beacons at diverse geographical locations of known finite distances from a ground station, each beacon transmitting by wireless link a unique range tone signal of constant frequency, the system comprising, in combination:

• a first receiver within the radiosonde for detecting the signals from the beacons;
• a transmitter coupled to said first receiver for retransmitting the signals;
• a second receiver at the ground station for detecting the retransmitted signals;
• a third receiver at the ground station for detecting the signals from the beacons;
• selector means coupled to said third receiver for selecting a unique signal transmitted by one of the beacons and for providing an address signal indicative thereof;
• filter means coupled to said selector means and said second receiver responsive to the address signal for passing the corresponding unique signal detected by said second receiver;
• generator means for providing outputs of the direction from the ground station to the radiosonde, and of the distance between the ground station and the radio beacon associated with the selected range tone;
• and
• computer means coupled to said filter means, said selector means, and said generator means for providing the line-of-sight distance from the ground station to the radiosonde.

A method for passively determining the distance from a ground station to a radiosonde comprising the steps of:

• launching a balloon carrying the radiosonde for drifting in the upper air;
• detecting at the radiosonde range tone signals of substantially constant frequencies from remote transmitters at diverse geographical locations of known finite distances from the ground station, said signals being unique for respective ones of said transmitters;
• retransmitting from the radiosonde the range tone signals;
• detecting at the ground station the retransmitted range tone signals;
• detecting at the ground station the range tone signals directly from the remote transmitters;
• selecting one of the unique range tone signals detected at the ground station from the respective remote transmitter;
• comparing the phase of the selected range tone signal with the corresponding retransmitted range tone signal detected at the ground station;
• determining the direction from the ground station to the radiosonde;
• and determining the distance from the ground station to the radiosonde as a function of the phase comparison, the determined direction, and the distance from the ground station to the remote transmitter associated with the selected range tone signal.