A system for transmitting television signals on a radio link. The system includes a transmitter having a modulator for modulating a carrier signal to produce a vestigial sideband amplitude modulated signal for transmission. The modulator includes a first converter for converting the frequency of video signals to an intermediate frequency and a second converter for converting the intermediate frequency of the video signals to a radio frequency. The system further includes a receiver having a demodulator for demodulating a received vestigial sideband amplitude modulated signal. The modulator includes a Nyquist filter connected between the first and second converters, and the demodulator includes a filter having a rectangular characteristic for processing the signal to be demodulated.

Transmission system for TV signals on radio links

An envelope detector with an extended linear dynamic range. A first amplitude modulated carrier signal, which can be of an intermediate frequency, is supplied to a first input terminal of a mixer, preferably balanced. The said first signal is also amplified and limited to produce a second signal which is phase synchronized with the carrier signal of said first signal, and which is supplied to the local oscillator input terminal of the mixer. The mixer responds to said first and second signals to produce a substantially dc (baseband) output signal whose waveform is similar to the envelope of said first signal.

Envelope detector using balanced mixer

SYNCHRONOUS DETECTOR PARTICULARLY ADAPTED FOR A VIDEO IF SIGNAL ABSTRACT OF THE DISCLOSURE A synchronous detector adapted to detect a modulated information signal, such as a video IF signal. The modulated information signal is provided in the form of a vestigial side-band signal. A band-pass filter including a tuned circuit tuned to the frequency of the carrier on which the information signal is modulated has a pass band which is less than the frequency spectrum of the vestigial sideband signal so as to limit the frequency spectrum of the signal passed by the filter to a double sideband signal. A limiter is coupled to the band-pass filter to receive the double sideband signal and for deriving a switching carrier therefrom, the frequency of the switching carrier being equal to the frequency of the carrier on which the information signal is modulated. An emitter-follower circuit is connected between the band-pass filter and the limiter so as to couple the double sideband signal from the filter to the limiter. A multiplier circuit has first input terminals coupled to the limiter for receiving the derived switching carrier and second input terminals for receiving the modulated information signal, whereby the modulated information signal is multiplied with the switching carrier to obtain the information signal. -i-

Synchronous detector particularly adapted for a video if signal

Demodulating apparatus for a modulated signal comprised of a carrier deriving circuit which is supplied with the modulated signal and which derives an unmodulated carrier therefrom, the carrier deriving circuit including a tuned circuit having a center frequency substantially coincident with the carrier frequency of the modulated signal and a limiter circuit in which the limiter circuit imparts a phase shift to the signal supplied thereto in connection with its elimination of the amplitude fluctuations in the signal produced by the tuned circuit. A synchronous detector receives the modulated signal and the derived carrier so as to detect the modulated signal with the derived carrier. A phase shift circuit supplies the synchronous detector with a phase shifted modulated signal, the phase shift substantially compensating for the phase shift imparted by the limited circuit in the carrier deriving circuit, whereby the modulated signal and the carrier which are applied to the synchronous detector are substantially in phase with each other.

Demodulating apparatus with phase shift compenstion

A first modulation at an arbitrary frequency and a second modulation at an arbitrary frequency. Demodulation (844) uses (838) the same reference oscillator signal as modulation (816, 820). Subsequent re-modulation (858) can be readily achieved at a second arbitrary frequency (864).

Method and system for re-modulation using zero if

An arrangement for carrier recovery in carrier frequency video and data transmission systems comprising transmitting and receiving converters which operate with over modulation has a suppressed carrier modulator in the transmitting converter with a Nyquist filter connected to its output for creating a vestigial side band and a pre-emphasis circuit connected at the input for strongly damping low frequency signals so that a degree of modulation of less than 100% results in carrier frequency signals. The receiving converter includes a carrier recovery device having a band pass filter followed by a limiter. The limiter is connected to a demodulator and a de-emphasis circuit is connected to the output of the demodulator.

Guenther Pexa

Papers

Arrangement for carrier recovery in carrier frequency video and data transmission systems

Schaltungsanordnung zur Traegerrueckgewinnung bei TF-Video- und Datenuebertragungssystemen