Abstract: A miniature handheld receiver contained in a metal shielding enclosure incorporating a slot type directional antenna as a part of the structure such that when the antenna is aligned with a radio frequency signal of interest, a null is produced in the signal level. The antenna is coupled to receiver circuitry which includes an oscillator used to FM modulate the signal by tone injection when an unmodulated carrier is present, an FM detector for demodulating the RF signal, an audio amplifier for amplifying the demodulated audio and an acoustically coupled earphone to prevent stray RF pickup from the earphone cord.

Abstract: A variable aperture direction finding system which uses a circular array of vertical receiving antennas connected to a capacitive type goniometer located in the center of the array to receive signals from radio frequency transmission sources. The goniometer has a stator plate for each antenna and a number of rotor plates which allow for the provision of selecting suitable apertures and antenna combinations to form Lobe or Split-lobe directional patterns. The goniometer's rotation is controlled by a servo drive system which provides for both manual positioning as well as automatic operation from a remote control unit.The system utilizes a remote control panel to allow selection of either manual or automatic rotation, azimuth indication, aperture and pattern selection, and manual positioning of the goniometer.An azimuth indicator system is driven in synchronization with the goniometer.

Abstract: An automatic radio direction finding (ADF) system having inputs for four quadrature antennas each having a cardioid pattern. Each input is amplitude modulated in quadrature and then combined in a hybrid circuit to produce a nondirectional pattern. The combined rf signal is carried through the receiver as a normal signal and the AM detected intermediate frequency of the receiver is fed to a processor. The sum quadrature modulation is recovered, filtered, and accumulated in such a manner that random signals will cancel and any repetitive signals at the modulation frequency will increase in amplitude and be stored. The vector information of this recovered modulation when decoded with respect to the phase of the original modulation, contains the actual bearing information. The signal is then averaged over several cycles and displayed in digital format in degrees of azimuth with respect to car heading. This averaging eliminates jitter in the last digit of the numerical readout.