Abstract: Apparatus and a method are disclosed for synthesizing a pseudorandom communications signal having a smooth, flat, power spectrum. The system comprises frequency modulation circuitry for deriving a first analog signal from a digital encoding signal. The first analog signal is derived to have a substantially constant amplitude and a frequency varying in response to the amplitude of the digital encoding signal. Fourier transform circuitry is connected to the modulation circuitry and is operative to derive a second analog signal from the first analog signal. The resulting second analog signal is the fourier transform of the first analog signal, having a substantially constant power spectral density over the bandwidth of said second analog signal, and having an amplitude that varies in response to the amplitude of the digital encoding signal.

Abstract: A Minimum-Shift Keying (MSK) modulator is described, wherein a feedback scheme is used in combination with a precise frequency reference to enable the production of MSK modulation at the output of an off-the-shelf voltage controlled oscillator (VCO). The upper and lower drive voltages for the VCO, corresponding to the upper and lower frequencies characteristic of MSK, are individually and independently corrected to compensate for imprecisions or fluctuations in the VCO characteristics. The correction increments are derived from phase excursion measurements over individual keying intervals.

Abstract: Method and apparatus are disclosed for improving the anti-jam performance of a processing circuit to increase conversion gain and reduce small signal suppression resulting from processing a phase modulated input signal accompanied by jamming interference. Input signals are each segregated into signal chips by a matched filter 23, and by an adaptive threshold circuit 13 in accordance with a predetermined relative threshold. The threshold is set to repeatedly distinguish a predetermined number of signal chips having greater signal amplitude. The absolute amplitude threshold level may, therefore, vary in accordance with the particular signal chips forming each input signal segment. A phase quantizer 29 operates to extract phase information from the signal chips.

Abstract: A method is provided for achieving initial synchronization of the transmission and reception of a frequency hopped communication signal, which comprises the steps of transmitting a preamble defined by a sequence of synchronizing pulses on a single channel and transmitting random dummy pulses over the remaining channels to hide the preamble. The received signal is filtered to obtain the preamble which is then convolved with a stored replica of the preamble to produce a synchronizing signal that is used to synchronize frequency hopping of the receiver and transmitter in preparation for the transmission of information. The received, constituent pulses of the preamble are delayed and accumulated by a baseband correlator (18) to form a composite pulse whose magnitude is detected by a threshold detector (20). The threshold detector produces the synchronizing signal (22) when the accumulated pulse reaches a prescribed value indicating that all of the bits of the preamble have been received.

Abstract: A pseudorandom noise generator which operates in different modes is disclosed. The pseudorandom noise generator (10) includes circuitry (11,13) for providing a digital signal having a pseudorandom sequence at a selected clock rate; a modulation control circuit (15, 17, 20, 23) for selectively providing a modulation control signal that corresponds to either a non-filtered or filtered version of the digital signal, and for controlling the mode of operation of the noise generator; a modulation circuit (27, 29, 31, 33) responsive to the modulation control signal for providing a modulation signal; and a voltage controlled oscillator (VCO) (35) responsive to the modulation signal for providing a VCO output having a relatively constant output spectrum and high spectral containment for each mode of operation pursuant to control by the modulation control circuit and the modulation circuit.