Automatic direction finding system

Apparatus for use in an automatic direction finding system, the combination comprising:

• a. a radio receiver for receiving audio signals from modulated radio frequency signals, said receiver having an antenna input terminal and an audio output terminal;
• b. a first directionally sensitive antenna means for providing information about a received signal for a first vector, said first vector being a component of the direction from which said received signal arrived;
• c. a second directionally sensitive antenna means for providing information about a received signal for a second vector, said second vector being a component of the direction from which said received signal arrived, said second directionally sensitive antenna means being oriented to be directionally sensitive in a different direction than said first directionally sensitive antenna means;
• d. means for alternately, at a first rate, making said first antenna means and said second antenna means operatively coupled to the antenna input terminal of said radio receiver;
• e. means for modulating received signals from said first and second antenna means to incorporate said directional vector information as modulation which is at an audio frequency rate, said audio frequency rate being substantially greater than said first rate;
• f. detection and storage means coupled to said audio output terminal for alternately, and in synchrony with said first rate, detecting the audio frequency information and separately storing it to establish individual vector values for each said antenna means;
• and
• g. indicator means responsive to said stored information to indicate the actual direction represented by the stored values.

Apparatus for use in an automatic direction finding system, the combination comprising:

• a. first directionally sensitive antenna means for providing information about a received signal for a first vector, said first vector being a component of the direction from which said received signal arrived;
• b. second directionally sensitive antenna means for providing information about said received signal for a second vector, said second vector being a component of the direction from which said received signal arrived;
• c. multiplexing means for processing said received signal (1) to be modulated to include include a first constant frequency audio component at a level corresponding to said first vector and having at least several adjacent audio frequency cycles corresponding to said first vector and (2) to be modulated to include a second constant frequency audio component at a level corresponding to said second vector and having at least several adjacent audio frequency cycles corresponding to said second vector;
• d. audio detecting means to detect an audio signal from said multiplexed received signal;
• e. vector detector means to separately detect from said audio signal signals corresponding to said first and second vectors;
• and
• f. indicator means responsive to said vector detector means to indicate the actual direction from which said received radio frequency signal arrived.

A direction finding antenna array for use with a frequency modulation receiver having an antenna terminal to receive a frequency modulated audio frequency signal and for use with an FM automatic direction finding system having first and second antenna commutation switching signals, said direction finding antenna array comprising:

• a. first pair of antennas means, said pair of antennas means spaced less than one half wavelength apart and first switching means for switching between said first pair of antennas means in response to said first antenna commutating switching signal;
• b. second pair of antennas means orthogonally opposed to said first pair of antennas means, said second pair of antennas means spaced a distance equal to the spacing of said first pair of antennas means and second switching means for switching between said second pair of antennas means in response to said second antennas commutating switching signal;
• and
• c. means for connecting together the outputs of (1) said first antenna means switched by said first antenna commutating switching signal and (2) said second antenna means switched by said second antenna commutating switching signal, whereby said switched rf signals may be connected to said antenna terminal of said frequency modulation receiver through a single coaxial cable.

An automatic direction finding system used with an FM receiver having an antenna terminal to receive a frequency modulated radio frequency signal and an audio output terminal said combination comprising:

• a. oscillator means to generate a clock source of frequency;
• b. divider means connected to said oscillator means to selectively divide said frequency of said oscillator means and generate chopper signals;
• c. latch means connected to said divider means to retain a selected count of said divider means;
• d. segmented circular display means connected to said latch means to display the retained count;
• e. switching signal means connected to said divider means to generate antenna commutating switching signals and synchronous detector switching signals;
• f. sweep display means connected between said oscillator means and said switching signal means and to said latch means to sequentially illuminate said display means in a circular direction when said receiver is not receiving a radio frequency signal of sufficient strength;
• g. direction finding antenna array means including antenna means orthogonally positioned with respect to each other, switching means for switching said antenna means and said antenna means switched by said antenna commutating switching signals of said switching signal means and said antenna means connected to said antenna terminal of said FM receiver;
• h. first filter means connected to said audio output terminal of said FM receiver;
• i. synchronous detector means serially connected with buffer means to said first filter means to process vector information for each of said antenna means and said synchronous detector means switched by said synchronous detector switching signals of said switching signal means;
• j. chopper means connected to each of said buffer means and switched by said chopper signals of said divider means;
• k. second filter means connected to said chopper means to integrate said filter said signals from said chopper means and outputting a signal having a phase component;
• and
• l. sweep signal control means connected between said second filter means and said latch means to detect a zero crossover of the phase component of said signal from said second filter means whereby said sweep signal control means latches said latch means on a count of said divider means and said divider means phased locked to said chopper signals thereby selectively illuminating a segment of said display means indicating the direction of arrival of the rf signal received by said direction finding antenna array means.

In a combination of an automatic direction finding system used with an AM receiver having an antenna terminal to receive an amplitude modulated audio frequency signal, having an audio output terminal and generating an automatic gain control signal, said combination comprising:

• a. oscillator means to generate a clock source of frequency;
• b. divider means connected to said oscillator means to selectively divide said frequency of said oscillator means and generate chopper signals;
• c. latch means connected to said divider means to retain a selected count of said divider means;
• d. segmented display means connected to said latch means to display the retained count of said latch means;
• e. switching signal means connected to said divider means to generate loop antenna commutating switching signals, synchronous detector signals, and a loop commutating signal;
• f. sweep display means connected between said oscillator means and said switching signal means and to said latch means to sequentially illuminate said display means in a circular direction when said receiver is not receiving a radio frequency signal of sufficient strength;
• g. direction finding antenna array means including two loop antennas means orthogonally positioned with respect to each other and a sense antenna positioned at the intersection of said loop antenna means;
• h. loop antenna selector means connected to each of said loop antenna means and switched by said loop antenna commutating switching signals of said switching signal means;
• i. loop antenna phase splitter means serially connected to said loop selector means;
• j. loop commutator means connected to said phase splitter means and switched by said loop commutating signal generated by said switching signal means;
• k. automatic gain control and threshold adjustment means connected to said AM receiver;
• l. first filter means connected to said audio output terminal of said AM receiver;
• m. synchronous detector means serially connected with buffer means to said first filter means to process phase information for each of said loop antenna means and said synchronous detector means switched by said synchronous detector switching signals of said switching signal means;
• n. chopper means connected to each of said buffer means and switched by said chopper signals of said divider means;
• o. second filter means connected to said chopper means to integrate and filter said signals from said chopper means outputting a signal having a phase component;
• and
• p. sweep signal control means connected between said second filter means and said latch means to detect a zero crossover of the phase component of said signal from said second filter means whereby said sweep signal control means latches said latch means on a count of said divider means and said divider means phased locked to said chopper signals thereby selectively illuminating said display means indicating the direction of arrival of the rf signal received by said direction finding antenna array means.

An automatic direction finding signal processor, for use in an automatic direction finding system having synchronous detector and chopper switching signals phase locked, which processes a demodulated audio output signal from a receiver having direction finding antenna means, said signal processor comprising:

• a. first filter means connected to said audio output terminal of said receiver to filter said carrier phase shifted signal from said audio signal;
• b. synchronous detector means serially connected with buffer means to said first filter means to process phase information for each of said means and switched by said synchronous detector antenna means and said synchronous detector switching signals of said automatic direction finding system;
• c. chopper means connected to each of said buffer means and switched by said chopper switching signals of said automatic direction finding system;
• d. second filter means connected to said chopper means to integrate and filter said signals from said chopper means outputting a signal having a phase shift component indicative of the direction of arrival of the received rf signal;
• and
• e. control means connected to said second filter means to detect a zero crossover of said phase component of said signal whereby said zero crossover point is indicative of the direction of arrival of the radio frequency signal.

In apparatus for use in an automatic direction finding system, the combination comprising:

• a. indicator means suitable for display of directional information of a received radio frequency signal and including:
• (1) an oscillator means to generate a clock source of frequency;
• (2) divider means connected to said oscillator means to selectively divide said frequency of said oscillator means and generate phase coherent chopper signals;
• (3) latch means connected to said divider means to retain a selected count of said divider means;
• and
• (4) display means connected to said latch means to display the retained count of said latch means;
• and
• b. direction determining means including:
• (1) means for obtaining two individual vector value signals which are representative of vector components of the direction of arrival of the received radio frequency signals;
• (2) chopper means for chopping said vector value signals in response to said chopper signals and for combining the chopped signals;
• and
• (3) phase detector means responsive to the phase of the combined chopped signal for latching said latch means in synchrony with the phase of the combined chopped signal.