Transmitter location system for frequencies below HF

Claim 1

Apparatus for locating unknown transmitters over great distances at a frequency f below HF comprising: a plurality of separated time synchronized receiver sites, each of said sites comprising a local station and a remote station separated a known baseline distance ΔR with respect to each other; receiver means at said remote station and said local station for producing a remote IF output and a local IF output, respectively, in response to received signals from an unknown transmitter having a bearing θ and a range D measured from the center of said baseline distance; data link means for coupling said remote output to said local station; phase comparator means at said local station for measuring the phase difference between said remote output and said local output, wherein said phase difference is related to said bearing; and, calibration means at each of said stations for phase synchronizing said stations with respect to each other whereby signals received from a transmitter located at a point equidistant from said stations produces a zero phase difference measurement at the output of said phase comparator.

Claim 3

A method for locating unknown transmitters over great distances at a frequency f below HF comprising the steps of: receiving signals transmitted by an unknown transmitter at different separated and time-synchronized pairs of local and remote receiver stations; phase synchronizing each of said pairs to produce zero phase differential when signals are received from a transmitter located equidistant from said local and remote stations; and, measuring the phase difference between signals received at said stations whereby said phase difference is directly proportional to the cosine of the bearing from the midpoint of a line between said stations to said unknown transmitter.

Claim 4

A method for locating unknown transmitters over great distances at a frequency f below HF comprising the steps of: receiving signals transmitted by an unknown transmitter at different separated and time-synchronized pairs of local and remote receiver stations; phase synchronizing each of said pairs to produce zero phase differential when signals are received from a transmitter located equidistant from said local and remote stations; and, measuring the phase difference between signals received at said stations whereby said phase difference is directly proportional to the cosine of the bearing from the midpoint of a line between said stations to said unknown transmitter.