 |
HISTORY
Problems with reception of television and radio
signals raised simultaneously with the
transmission of the first television programs in
the 30-th.
Up to 50-th there were not a
lot of owners of TV sets and they were receiving
the signal with individual antennas. After the
II World war the extension of house-building
resulted a lack of space on the roofs for
individual antennas installation. Solution was
founded in installation of one receiving TV
antenna for one building. This way of TV
programs' distribution was called TV Multiple
Receiving System (TMRS).
This system
had become so popular in our society that now in
every building project they use such system.
Such technical solution permitted to reduce the
number of receiving antennas up to one for the
whole building and to achieve a better quality
of TV signal.
Further development of
many-storied house-building in 60-70-th
negatively influenced the quality of the
reception of TV signal even in the areas with a
consistent TV signal reception. In 60-70-th
there were a lot of claims concerning the
receiving devices operation after the
introduction of color TV.
Almost
simultaneously in the USSR and in the USA the
devices allowing to connect tens of TV sets to
one antenna were designed. These systems had the
similar structural principals, though they
solved different problems. In the USSR first of
all the TMRS was created as a mean for
distribution of TV signals among the multilevel
buildings to limit the number of individual
outdoor antennas. In the USA, similar systems
were used first of all to provide TV reception
in the regions with low field strength. Systems
containing high-performance antenna devices and
cable distribution network have made it possible
to extend an active area of TV transmitters.
The investigations and the maintenance
experience shows that TMRS is the most efficient
way of receiving networks creation. It has good
performance characteristics and provides an easy
way to create the receiving networks in case of
multiprogram broadcasting and also the better
coupling with the transmitting network together
with the possibility to use the normal TV
sets.
The mentioned
circumstances determined the wide spread and
rapid development of TMRS all over the world.
During the short period of time the systems
characteristics have grown up immensely
providing the sufficient improvement of the
quality of transmitted signals' quality and the
increase of their number. That allowed the users
to receive the radio programs and additional
information together with normal TV programs and
also to increase the number of users of one
system.
The
initial TMRS settings were designed for user
service in separate part of many-storied
building (normally from 10 to 50 subscribers).
For these purposes different types of receiving
TV antennas were designed, in particular
single-channel and double-channel antennas of
"wave channel" type operating on the
same frequency range with various channel
combinations as well as broadband ones for
operation in 5-7 channels.
Different types
of TV amplifiers (channel and wide-band types)
were designed and wide spread. They provided the
possibility of creation of receiving and
distribution signal systems in the ranges of
48,5-100 and 174-230 MHz. Firstly there
were vacuum tube amplifiers. Later the new
uniformed transistor TV complexes were designed.
It results higher reliability and economy of
TMRS.
Different
elements for splitting, alignment and filtration
of TV signals were designed for TMRS as well as
efficient subscribers' and distributing coaxial
cables.
Familiarization with UHF band
(470-790 MHz) for TV broadcasting needs required
for the diversification of equipment necessary
for TMRS creation. For these purposes UHF
antennas and converters were designed and
applied in industry. They provided the reception
and frequency conversion of any UHF band channel
to metric band channel (48,5…230 MHz).
It appears from the above-said that
initially the development of TMRS in our country
was directed to the modernization of the
existing equipment and did not affect the
principles of networking. According to this
policy "one antenna for one building"
systems had been
created.
With the
extension of the territory for TMRS installation
in the apartment and administrative buildings
the cases of unsatisfactory performance of TV
programs used to appear more often. The reasons
were the following: a lot of receiving antennas
turned out to be in the "shadow" zone
with an extremely low field strength or in zone
with high intensity of the delayed signal
determined by the reflection of electromagnetic
waves in the signal pass. This situation became
extremely difficult with the construction of new
buildings of different height. It resulted the
appearance of "distracted" areas
affecting the whole districts. The same
situation appeared with the reception of stereo
radio signals in intensive reflected signal
conditions.
The
executed researches shown that the most
effective solution of these problems was the
creation of large TMRS (LTMRS). Each of LTMRS
was designed to provide service for several
thousand of subscribers from a single antenna
located in a point with good receiving
conditions. They began the mass LTMRS
construction from the beginning of the 70-th.
However, they used the TMRS equipment in these
new systems that is why they couldn't provide
necessary quality and reliability of reception
of TV signal subscribers. The number of received
and distributed TV channels was limited by five
ones as Ostankino TV Tower had got only 5 TV
transmitters
and
there
were no plans to increase the
number of transmitted channels in the nearest
future.
At
the beginning of the 80-th the USSR Government
has paid attention to a problem of providing the
inhabitants with a high quality TV programs
reception and assigned necessary financial
resources for the development of new equipment
by issuing of the appropriate Decree. After that
they began to construct the LTMRS and Cable TV
Systems (CTS) everywhere. The classification of
television receiving systems has changed
slightly, so it began to look like this:
- TV Multiple Receiving System (TMRS).
- Large TV Multiple Receiving System (LTMRS).
- Cable TV Systems (CTS)
It
means that TMRS provide the service of
subscribers of one building, LTMRS - for tens of
buildings, CTS - for large city regions.
One
of the distinctive features of this stage was
the fact that all new constructed systems could
distribute only 5 TV channels and had
distributive network with the operating
frequency range of 40…240 MHz. Their only
difference from old systems was the utility of
broadband equipment with better technical
specifications instead of channel and band
equipment.
It is necessary to mark that the
indispensable condition of successful
development of CTS was the selection of such
scheme of construction that would allow using
LTMRS and TMRS as the lowest links of a
distributive network without essential
alterations. Otherwise, the implementation of
CTS in regions with complete building-up was
connected with some additional extra
investments.
At the
beginning of 90th practically all the territory
of Moscow was enveloped by LTMRS and CTS. With
the city population of about 10 millions the
total number of systems was about 3000 with the
number of subscribers about 22000. As before
these systems provided high quality reception
and distribution of 5 TV
programs.
In this
period of time the economical and political
situation in the country had been changed
sufficiently. Of cause all that influenced the
development of a cable
television.
Rapid
development of market economy, reversal of the
restrictions on a transmission of information,
sharp increase of quantity of transmitted TV
channels have changed a situation in a cable
television.
The
first sign of this marked by the viewer, was the
appearance of a large number of local cable TV
studios. Now in Moscow it is about 100 of them.
The large present cable networks have submitted
them a capability at minimum expenses to provide
the transmission of one TV channel. At the same
time, by the coupling of present systems with
the help of lines on a coaxial cable some
studios manage to increase an audience up to 100
and more than thousand viewers while
transmitting with one technical
hardware.
Only in 5 years
the number of TV transmitters on air at
Ostankino TV Tower has increased from 5 up to
13.
Therefore, in view of
one television channel reshaped by local cable
TV studio the inhabitant of Moscow could receive
today 15 television programs. The real situation
is the substantial part of city population is
provided with the reception in average only of 9
TV programs.
Besides the above-mentioned the Government of
city adopts the projects of creation of a
unified urban fiber optic network. The
implementation of this project is laid upon
Moscow Telecommunication Corporation. The
created fiber optic network is intended not only
for
the
transmission of high-speed digital volumes of
information, but also for TV signal distribution
control.
Today, it is possible to
tell that the time when it is necessary to look
at development of a cable TV from other points
of view has come.
It is clear, that
realization of activities on backfitting of the
existing receiving TV systems can not result the
desired effect because of the restricted
operational frequency band (the high limit of
distributive networks operational range is 230
MHz). The extension of this range up to 300 MHz
will not give an actual financial efficiency.
Only creation of modern cable TV systems with an
operational range up to 600... 800 MHz could
change a situation
considerably.
Unfortunately, now Russian companies do not
produce such professional cable TV equipment and
the only solution of this problem is to address
to the foreign companies.
The renovation of a
cable TV receiving network on a city scale is a
rather difficult technical-organizational and
financial problem. Such kind of activity should
be executed during a long period of time.
Therefore, today the most actual problem is
maximally effective usage of an existing cable
TV networks infrastructure. It should consist of
two primary goals.
The 1st: maximally
effective utility of the existing receiving TV
systems providing the reception and distribution
of the additional TV programs transmitted from
the Ostankino Tower. In this case it implies 27,
31, 35, 38, 49 and 51 frequency channels TV
signals. This problem now is successfully
deciding by MRC. The realization of activities
on backfitting of the existing equipment is in
the process now.
The
2nd problem envisions realization of activities
on distribution of the local television programs
including the municipal, prefecture, district
and metropolitan-area programs. Taking into
account rather low capabilities of the existing
cable distribution systems, unfortunately these
programs can be distributed only within one
frequency TV channel (the 5th one) which is
intended for Moscow. In this connection the only
possible decision in this situation is the time
division of broadcasting of the above-mentioned
programs within one frequency channel.
That is why
now the most actual problem is unification of
the existing LTMRS and CTS in a single whole. It
is necessary to create a unified cable network
in large urban areas, municipalities and
prefectures. The engineering state of the art
now allows to decide this problem on the basis
of utility of fiber-optic communication lines,
coaxial cable lines and radio-relay
equipment.
 Back to main page
|
|
)
)
)
)
)
