7 SUMMARY
The topic «transmission of an audio-video signal
frequency by Radio- relay system and satellite» is a topic, which calls
with a development, which is based at the same time on the genesis and the
relative topicality on television. A video signal crosses several stages before
arriving at its final destination. That passes by the production, the transport
and the diffusion of this signal. It should be noted here that we have the
video signals analogical and numerical. The signal digital video can be either
monochromic or composite. There exist several standards of television color.
The analogical signals are digitized according to standards given. Out of
digital television, one uses several standards of coding. It is: MPEG1, MPEG 2,
MPEG-4 and also the Eurocrypt standard. The audio signal, in what relates to
it, knows also stages. The production and the treatment of the audio signal are
subjected to modes of modulation. There exist two systems of modulation that
are the multiplexing and the demultiplexing. Also, let us underline that
various types of modulation are used namely: analogical modulations, multiple
analogical modulations, numerical modulations, elementary modulations, complex
modulations and the amplitude modulations. There exists a very varied range of
audio equipment to knowing the audio cables (the armor-plated audio cable, the
audio cable without shielding,the coaxial cable) and the connectors (Cards
CINCH or RCA, cards stereo jacks 3.5 mm and 6.35 mm, cards XLR, and cards DIN).
The transmission by Radio-relay system is done by the means of the Radio-relay
system which is a system of transmission of signals particularly analogical,
numerical mono-directional or side and generally permanent between two fixed
geographical sites. These emissions are in particular sensitive to maskings,
precipitations, the conditions of atmospheric refractivity, to the
electromagnetic disturbances and have a rather strong sensitivity, with the
phenomena of reflexion.Several equipments are used at the time of emission and
of reception per Hertzien. We have the Yagi aerial, the parabolic aerial, the
head HF, the transmitter, and the receivers. The propagation of the Hertzian
wave is often attenuated for several reasons: propagation in free space and
release, atmospheric refraction, phenomena of guidance, attenuations because of
the hydrometeors, release/diffraction. The transmission by satellite is done by
the use of the satellite, which is another mode of reception of television
after the terrestrial hertzian
reception. As equipment used for this connection one can
quote: the transmitter, transposor RF/FI/RF, the modulator, the shielded cable,
the connector of the type F etc... The reception by satellite is done through a
satellite station, which includes /understands: the parabola, the head or LNB
(universal, Twin, mono block, or Quattro), reflectors, the receiver, the
demodulator. The polarization of the transmission differs according to whether
one is in the presence of an analog transmission or a digital transmission. The
satellites use several frequencies. These last vary from an area to another.
The quality of reception of a televisual signal by Radio-relay System depends
on the influence of the propagation, of the influence height of antenna,
evaluation of the received real level and the calculation of the assessment of
connection. The quality of reception of a televisual signal by satellite as for
it is prone to the calculation of the assessment of connection for the up line
and that of the assessment of connection for the down line.
| 
