US 5,335,006 AGranted

Method and device for transmitting video signals in confined spaces

AssigneeCharbonnages de France

InventorsDominique Charpentier, Pierre DeGaugue, Daniel Degardin, Jacques Baudet

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Abstract

A UHF carrier signal modulated by a video signal, where the frequency and the format of a line synchronization signal are known, is transmitted in a transmission region in a confined medium by a microwave link. In a reception region, two signals are received along two angularly offset privileged axes, each is frequency-demodulated along identical processing channels, the existence in the signal emitted from one of the channels, the "starting channel", of a periodic signal with the line synchronization frequency is checked and this signal is selected if the check proves positive. If the periodic signal disappears, the test is applied to the other channel; if that check is positive, this other channel is selected until this periodic signal disappears. Such a process is especially applicable in tunnels.

Claims34

Dependent claims

A method of transmitting video signals formed by a succession of video picture line signals beginning with a known format synchronization signal of a known period representing a known line synchronization frequency between a transmission area and a reception area, both included in a confined space, comprising the steps of:

producing a first video signal in the transmission area;
modulating said first video signal at a carrier frequency in the microwave band to produce microwave transmission signals;
transmitting said microwave transmission signals from a transmitting antenna directed to the reception area provided with two receiving antennae, each receiving antenna provided on an angularly offset privileged axis with respect to each another;
receiving separate microwave transmission signals produced by said transmitting step in each of said two receiving antenna;
processing and demodulating said microwave transmission signals in separate but identified first and second demodulation and processing channels connected to a respective receiving antenna to produce a second video signal in said first demodulation and processing channel and a third video signal in said second demodulation and processing channel;
connecting said second video signal to a picture forming apparatus;
detecting, in said first and second demodulation and processing channels, the presence of a periodic signal with a frequency equal to the video line synchronization frequency in said second and third video signals;
and
connecting said third video signal to the picture forming apparatus if said periodic signal is no longer detected in said first demodulation and processing channel, but is detected in said second demodulation and processing channel.

6 more elements

A system for transmitting video picture line signals beginning with a known format synchronization signal with a known period representing a known line synchronization frequency between a transmission area and a reception area, both included in a confined space, comprising:

a video recording device producing a first video signal;
a modulation means connected to said video recording device for modulating said video signal at a carrier frequency in the microwave band to produce microwave transmission signals;
a transmitter associated with said video recording device and said modulation means for transmitting said microwave transmission signals in the confined space directly to the reception area, said transmitter including a first antenna;
a receiver means provided in said reception area for receiving said microwave transmission signals, said receiver means including second and third antennae with radiation patterns defining two angularly offset privileged axes;
first and second demodulation and processing channels, each of which is connected to the output of one of said second and third antennae, respectively, for demodulating said microwave transmission signals received by each of said second and third antennae to produce respective second and third video signals, said first and second demodulation and processing channels detecting the presence or absence of a periodic signal with a frequency equal to the video line synchronization frequency in said second and third video signals, said first and second demodulation and processing channels each producing an output including said second or third video signals and a signal indicating the presence or absence of said periodic signal;
an analyzer circuit connected to said first and second demodulation and processing channels for receiving said second and third video signals as well as said output indicating the presence or absence of said periodic signal, said analyzer circuit determining the reception quality of said second and third video signal as well as which of said second and third video signals should be displayed, said analyzer circuit producing an output;
and
a display device connected to said analyzer circuit for displaying either said second or third video signal, based upon said output produced by said analyzer circuit.

5 more elements

Dependencies are inferred from the claim text.