Abstract: A balanced modulator, producing a double sideband suppressed carrier (DSBSC) output achieves carrier suppression and linear performance suitable to modulate frequency division multiplexed signals with stringent interchannel interference requirements. It is simply and inexpensively realized through the use of two logic gates which are arranged in a dual complementary fashion, so that their output terminals go high and low alternately, and which drive a center-tapped transformer through coupling capacitors to provide the required switching function necessary to produce the DSBSC output. The modulator circuit has the added feature that the square wave carrier source that is applied to the logic gates can be the means of activating the circuit, thereby eliminating the need for a separate power supply.

Abstract: Source intelligence within a predetermined bandwidth is normally provided to a transmission channel having a bandwidth constraint of the predetermined bandwidth. For privacy transmission, a first pulse train indicative of the source intelligence is derived and is enciphered by addition of pseudo-random values to the pulses, either directly or modulo some specified constant. The enciphered pulse train is converted to first and second symbol pulse trains at subharmonic frequencies of the first pulse train. Energy within a selected spectrum is derived from each symbol pulse train, such as by filtering, and used to modulate first and second channels of a quadrature modulator having a carrier frequency centered within the predetermined bandwidth. A suppressed carrier quadrature modulated output is transmitted along with a carrier frequency component.

Abstract: Single sideband modulation system. A first single sideband of radio frequency is generated with first audio modulation on the lower side of an assigned frequency, the first single sideband bandwidth being equal to the highest frequency of said first audio modulation. A second single sideband of radio frequency is generated with second audio modulation on the upper side of the assigned frequency, the second single sideband bandwidth being equal to the highest frequency of said second audio modulation. A first stereo channel is modulated on the lower sideband frequency. A second stereo channel is modulated on the upper sideband frequency. The stereo channels are combined whereby a receiver tuned to the assigned non-transmitted carrier frequency will receive both stereo channels.

Abstract: A single sideband signal can be demodulated by using sampled data techniques. An intermediate frequency (IF) radio signal is split into two branches and is sampled by two sample and hold devices; each sample and hold device operates at a rate that is not only a submultiple of the carrier frequency, but is also at least twice the information bandwidth. Prior to, or during sampling of one branch (the quadrature branch), a Hilbert's transform is performed upon the IF signal which results in the output of the two sample and hold devices being in phase quadrature. A phase shift of 90.degree., using a baseband finite impulse response Hilbert's transform filter, is performed upon the output signal of the quadrature branch's sample and hold device. The sum of the inphase sampled signal and the filtered quadrature phase sampled signal produces the demodulated lower sideband while the difference between the two produces the demodulated upper sideband.