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 fast and inexpensive set-on oscillator is disclosed. According to the invention, the input signal is processed in two paths. In the first path, a coarse estimate of the input frequency is made. In the second path, the input signal is down converted to a baseband. The frequency of the relatively low frequency baseband signal is measured and a new signal at this frequency is synthesized. The synthesized signal is up converted in frequency. The down-conversion process is performed ambiguously and circuitry is included to resolve the ambiguity. The up conversion process is also performed ambiguously. The coarse estimate of the input frequency is used to resolve this ambiguity.

Abstract: A discrete coherent chirp generator capable of generating a plurality of coherent sinusoidal signals. The chirp generator comprises a programmable read only memory containing samples of one period of a sine wave. Additional circuitry generates addresses to the programmable read only memory at periodic intervals to cause samples of a sine wave of the desired frequency to be read out of the programmable read only memory. As a particular application, a plurality of frequency modulated signals can also be generated.

Abstract: A digital frequency synthesizer is provided for producing a signal having a predetermined frequency. Such system includes: a computer for calculating the residue of the frequency to be synthesized modulo a predetermined frequency, f.sub.LO, and the nearest modulus frequency; an intermediate frequency generator for generating an intermediate frequency signal having a frequency equal to the determined residue; a harmonic generator section for combining the intermediate frequency signal with a plurality of harmonics of the predetermined frequency, f.sub.LO, to produce a composite signal having a plurality of frequency components separated one from another by the predetermined frequency, f.sub.

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 digital memory system adapted to store a sequence of one bit quantized samples of an input signal having a frequency within a predetermined band of frequencies and to produce a replica of such input signal from such stored one bit samples. A control signal is produced indicative of the particular portion of the band of frequencies which includes the frequency of the input signal. A plurality of filters is provided, each one tuned to a different portion of the band. In response to the control signal the sequence of bits read from memory passes through the filter which is tuned to the portion of the band which includes the frequency of the input signal. With such arrangement many unwanted harmonics produced because of the one bit quantization of the input signal are removed.

Abstract: A digital frequency synthesizer is disclosed wherein a series of binary level signals are produced, the level of such signals changing at a frequency related to a selected frequency f. The synthesizer includes a counter which counts clock pulses fed thereto at a pulse repetition frequency f.sub.cp producing a first digital word representative of the number counted clock pulses. An adder cumulatively adds a second digital word representative of f.sub.cp /nf, where n is an even integer, each time the whole number portion of the cumulatively added second digital word equals the first digital word. A comparator produces a control signal indicative of whether the whole number portion of the cumulatively added second digital word is equal to the first digital word. A flip/flop, responsive to the control signal, produces a binary level signal, the level of such signal changing at a frequency related to the frequency f.

Abstract: A memory system adapted to receive a radio frequency signal and produce a signal having a frequency related to the frequency of the received signal for an extended, predetermined period of time. The received signal is heterodyned to an intermediate frequency signal. The intermediate frequency signal is sampled and digitized by an analog-to-digital converter. One bit of each digitized sample has a logic state related to the polarity of the intermediate frequency signal. The bits associated with the samples are stored for a time interval beginning at a time the intermediate frequency signal changes polarity with a predetermined sense, i.e. the start of a complete cycle of the signal. A control signal is produced providing an indication of the portion of the bits stored in the shift register at the end of the time interval which is associated with complete cycles of the stored signal and the portion of the stored bits which is associated with an incomplete cycle of the stored signal.

Abstract: An electronic countermeasure system wherein signal processing apparatus is included to enable only a predetermined number of digital words associated with one of a plurality of radio frequency energy sources to pass to a general purpose digital computer. Also, such signal processing apparatus modifies the digital word passed to such digital computer to simplify the processing required by such digital computer.

Abstract: A frequency measuring apparatus is disclosed wherein a plurality of sets of harmonic signals is mixed with a received signal to produce a plurality of groups of beat frequency signals. A plurality of filters, each one being fed by a corresponding one of the groups of beat frequency signals, is provided to reject the beat frequency signals in such group having frequencies greater than one-half the fundamental frequency of the set of signals producing the group of beat frequency signals fed to such one of the filters. A plurality of counters, each one coupled to the output of a corresponding one of the filters, converts the frequency of the beat frequency signals fed to such counter to corresponding digital words. A logic network is provided to calculate the frequency of the received signal from the digital words provided by the counter.