Telecommunications – Wireless distribution system
Patent
1991-02-04
1994-01-04
Eisenzopf, Reinhard J.
Telecommunications
Wireless distribution system
455 62, 455131, 455275, 455282, 455293, H04B 116
Patent
active
052769046
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a direct demodulation microwave frequency head allowing the reception of television or telecommunications signals retransmitted by a terrestrial satellite. This unique head, located in the vicinity of the parabolic receiving antenna, allows the simultaneous demodulation of several transmission channels from among all the channels available on several satellites. It is connected to the multiplexer of an existing UHF and VHF microwave link receiving antennas and, because of this, uses the existing UHF-VHF down lead to the television receiver, or telecommunications equipment.
2. Discussion of the Background
One of the difficulties associated with the reception of signals retransmitted by satellites is caused by the multiplicity of the forms of retransmitted signals depending on:
the orbital position of the satellites located, for France, between 20.degree. East and 40.degree. West,
their carrier band frequency between 11 GHz and 12.8 GHz
the type of polarization of the wave transmitted by the satellite which is linearly polarized in the vertical or horizontal direction, or left or right circularly polarized.
This latter characteristic is related to the technology and type of source of illumination of the antenna and is excluded from the scope of the invention but the receiving electronics must still be able to be compatible with all of the covered bandwidth which is, at present, a bandwidth of the order of 1.8 GHz.
According to the prior art, the structure of a satellite TV reception system comprises two subassemblies: an external unit, located for example on the roof of a building, and an internal unit which is often in the form of a cabinet slid under the receiver.
The function of the external unit is:
to pick up the energy transmitted by the satellite by means of an antenna,
to amplify the received signal (about -80 to -90 dBm per channel),
to transpose the received signal (bands 10.95 to 11.7, 11.7 to 12.5, 12.5 to 12.75 GHz) into an intermediate frequency band of 950 to 1700 MHz.
The function of the internal unit is:
to select the channel to be received by means of a synthesizer and a frequency converter. A surface wave filter, normally a 480 or 612 MHz filter, allows the elimination of the adjacent channels.
to demodulate the frequency modulated signal by means of:
either a standard frequency discriminator,
or a phase locked loop allowing an increase in the sensitivity threshold of the demodulator (gain of 2 to 3 dB approximately).
The essential advantage of this structure is that it minimizes the complexity of the external unit.
In the case of the simultaneous reception of several satellites, each satellite requires a specific receiving antenna. It is therefore necessary to provide, between the external units (antennas and converters) and the internal units (satellite demodulators) as many down leads as there are satellites. When two different polarizations are used simultaneously on a same satellite, it is necessary to provide a switching of the intermediate frequencies, or two antenna down leads per satellite.
In the case of the sequential reception of several satellites, it is possible to simplify the problem by means of a switching box which allows the choosing of "n" outputs from among "p" possibilities and the routing of them to the users concerned. The limit case is of a single user who wishes to sequentially receive one polarization from one satellite at a time. In this case therefore a multi-satellite antenna is necessary which is electrically aimed at the chosen satellite and which has the number of types of microwave frequency sources and of compatible converters.
But in addition, recent television sets have a video frequency picture-in-picture channel which allows the simultaneous observation of what is happening on a main program and on another program for the purpose of recording it.
It is necessary to be able to have the simultaneous availability of:
a main program
any program in a picture-in-picture
REFERENCES:
patent: 4608710 (1986-08-01), Sugiura
Bert Alain
Cluniat Claude
Mutzig Jean-Paul
Eisenzopf Reinhard J.
Pham Chi
Thomson Composants Microondes
Thomson-LGT Laboratoire General des Telecommunications
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