Abstract: Apparatus for detecting FM signals, such as from a radio altimeter, is disclosed. The apparatus contains a phase detector which has as inputs the received signal and a delayed replica of the input signal. The output of the phase detector is filtered in a filter bank, the outputs of which feed a logic circuit. The logic circuit selects the output with the largest signal level. If the selected output has a level exceeding a threshold, the presence of an FM signal is indicated.

Abstract: A memory system adapted to store samples of a finite portion of a periodic signal and produce an output signal having the same frequency as the periodic signal for a relatively longer time duration. The system includes a network for comparing the initial and terminal portions of the finite portion of the stored signal to determine the relative phase shift therebetween. Portions of the samples of the stored periodic signal and of the phase delayed replicas which extend from the first sample to the next to the last sample thereof are sequentially coupled to an output selectively in accordance with the determined relative phase shift to produce the output signal.

Abstract: A digital memory system is provided wherein a received radio frequency signal is separated into a pair of quadrature signal channels, the signals in each one of the channel being sampled and stored in a digital memory at a rate substantially lower than the Nyquist sampling rate. During recall the stored samples are sequentially read from the memories at the rate at which they were stored. The samples read from the memories in each of the channels are sampled at the relatively low sampling rate and are then combined into a single channel after shifting the phase of the signals in one of the channels 90 degrees, to form a composite signal having a plurality of radio frequency signal components, each one being separated in frequency from another one by an amount having a predetermined relationship to the pulse repetition frequency of the sampling pulses; one of such radio frequency signal components having the frequency of the received signal.

Abstract: A digital memory system is provided wherein a received radio frequency signal is separated into a pair of quadrature signal channels, the signals in each one of the channel being sampled and stored in a digital memory at a rate substantially lower than the Nyquist sampling rate. During recall the stored samples are sequentially read from the memories at the rate at which they were stored. The samples read from the memories in each of the channels are sampled at the relatively low sampling rate and are then combined into a single channel after shifting the phase of the signals in one of the channels 90 degrees, to form a composite signal having a plurality of radio frequency signal components, each one being separated in frequency from another one by an amount having a predetermined relationship to the pulse repetition frequency of the sampling pulses; one of such radio frequency signal components having the frequency of the received signal.

Abstract: A digital memory system adapted to store samples of a received radio frequency signal and enable retransmission of a radio frequency signal from such stored samples, such retransmitted radio frequency signal having a frequency related to the frequency of the received radio frequency signal. The received signal is heterodyned to a periodic sinusoid video frequency signal having a predetermined average level. A sequence of one-bit logical signals representative of the amplitude of the video signal relative to a predetermined level other than the predetermined average level is stored. The stored samples are returned and converted to a radio frequency signal having a frequency of the received signal. By using a non-average level as the threshold voltage, the spectrum of the signal retrieved from the memory will have reduced harmonic components relative to the fundamental frequency component.

Abstract: A multiplexer circuit is disclosed wherein a diode ring circuit is coupled to a pair of logical signal sources and a first winding of a transformer. A second winding of the transformer is coupled to a control signal source. One of the pair of logical signal sources is coupled to a center tap of the first winding selectively in accordance with the control signal.

Abstract: A radio frequency signal direction finding system wherein radio frequency signals received at output ports of a multibeam array antenna are sequentially sampled, in response to a sampling signal, at a frequency f.sub.s. The sampled signals are fed to a receiver channel which is tuned to the sampling frequency to produce a composite signal having a frequency f.sub.s and a phase angle, relative to a reference phase angle of the sampling signal, which provides an indication of the relative signal levels received at the output ports and hence an indication of the angular direction of a source of the radio frequency signals.