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```									                           TV standards and the cable used to transport these signals into a community TV Network

The Decibel
Because of the use of the decibel measurement system in the following paragraphs, you will be introduced to it at this point.

In this document we are going to show gain and attenuation in dB, (gain or loss), dBuV (microvolt) and dBmV (millivolt)

The Decibel (dB) is used as a measurement system. It is often used for equipment gain ratings .

dB (Decibel) is a unit that expresses the logarithmic ratio between the input and output of any given component, circuit, or system and may be expressed in terms of
voltage, current, or power.
Gains and losses are not linear, and neither is the way you hear sound, therefore logarithmic values have to be applied, (remember your log tables book at school?)

The formulas used are relatively complex, however that is of no concern in this document since all the formula calculations have been done by the equipment
manufacturers and they are already expressed in dB.

Most often it is used to show the ratio between input and output power or voltage

Let's go then
Coaxial (Coax) cable characteristics
Coaxial cable by it's nature contains impedance ( A measure of the opposition to the flow of an alternating current in a cable)

This causes a problem with Television and Radio frequencies because this character changes with the frequency of the signal, the higher the frequency
the more it is attenuated by increasing the cable length. In basic terms this would mean the degradation of the signal mainly to it's amplitude and also to it's quality.

The higher the frequency the more it is attenuated by the cable, this is a fact!

The best way is to lower these frequencies (If possible) so that the TV/Radio signal will travel the required distance, without unnecessary amplification.
In a small urbanisations or a block of apartments high frequencies can be used since the distance they will travel is relatively small.

However, in larger urbanisations when cable runs are long it is necessary to either

(1) Use a cable that will attenuate the signal less!
(2) Amplify the signal at strategic points to maintain an acceptable level (this introduces noise)
(3) Lower the frequency so that it will travel further.

MULTI – SPLITTER (QPSK – SAT-IF) systems use high frequencies, 950 MHz – 2150 MHz, so high in fact that it is above the UHF band and into the
Microwave band.

These systems if incorrectly installed are characterised by white cable (RG 6 type) which is available from any DIY store and generally installed by
untrained - non qualified engineers, that in the terms of the Spanish are called “vaqueros”

These Multi- Splitter systems were designed for Apartment blocks where the cable runs are less than 100m, the advantage of them is that up to
200 TV channels can be achieved but 95% of these channels are rubbish anyway.

These systems if installed correctly will consume many hundreds of metres of cable since the main signal trunk requires 4 of them, 1 for each
polarity.

SINGLE USER
Satellite dish                This shows that a Set top Box 100m away from the source would work OK since the input level
dBμV
requirement for this type is 44 dBμV (-16 dBmV) and the level is 60dBμV (0dBmV)
Input level 60dBμV
Network Amplifier            Satellite TV Cable ( RG6) as available from most DIY stores usually white, not designed for underground.
and Distribution                                                                    100m           Average Cable loss -25 dB                            Set Top Box
100m away
Output level 85 dBμV (25 dBmV) average for Costa Blanca                                                                                                    from source
Now that is OK if you only have 1 user attached and they are 100m away from the source, however, it is not that easy there are normally dozens
of users connected, lets base our calculations on only 8.
In this case we need a special splitter called a Multi-user splitter, now these by their very nature split the signals)

These Splitters have ...
(1) Tap loss and
(2) Through Loss
both are measured in dB, so generally about 24 dB per user

This shows 8 Set top Box 100m maximum away from the source would not work OK since the input level
44dBμV                               dBμV
requirement for this type is 44dBμV (-16dBmV) and the level is 36 dBμV (-24 dBmV) , what would happen would be serious picture break-up
8 USERS
Satellite dish

Satellite TV Cable ( RG6) as available from most DIY stores usually white, not designed for underground.
Input level dropped to 36 dBμV
Head End                                                                                                                                   for a cable run of 100m
Max average Cable loss -25 dB + Multi-Splitter losses - 24dB
Network Amplifier
and Distribution             Multi-Splitter
Through losses
and Tap losses                                         Up to a max of 100m cable lengths
Output level 85 dBμV
(25 dBmV)                   -24 dB
average for Costa Blanca

What would the “Vaqueros” do? Stick in and Amplifier/Splitter half way down the line, bodged!!.. the amplifier gain should be set to increase
the levels so that the Set top Box sees a signal level of about 66 dBμV (6 dBmV) for continuous operation levels, this is a gain of 30 dB , twice the maximum most
51dBμV,
amplifiers can output, so the amplifier would be set to max and the input level would raise to only 51dBμV just workable but not ideal, the Satellite footprint shrinks at
least twice per day and the signal levels will drop, also the installers have introduced noise into the system from the amplifier (set to max), what would happen?
Break up of the picture at specific times of the day if the Set top Box levels dropped to critical levels and the noise levels introduced by the amplifier caused the signal
quality (Carrier to Noise ratio/Signal to Noise ratio) to deteriorate, causing again picture break up.

What they should have done is installed the correct cable in the first place!
To improve this situation use RG11 type (UG) Underground cable, this is much larger in diameter, needs special connectors, and crimping tools which
cable
any professional installer would possess.

Lets have a look at the calculations............

This shows 8 Set top Box 100m maximum away from the source would work OK since the input level
44dBμV                               46dBμV    dBmV),
requirement for this type is 44dBμV (-16 dBmV) and the level is 46dBμV (-14 dBmV), but it is still close to the minimum operating
8 USERS                     level of the Set top Box, and picture break up could still occur.
Satellite dish

Satellite TV Cable ( RG11 UG) as available from specialist suppliers usually black, and designed for underground.
Input level dropped to 46 dB
Head End                                                                                                                                  for a cable run of 100m
Max average Cable loss -15.00 dB + Multi-Splitter losses - 24dB
Network Amplifier
and Distribution               Multi-Splitter
Through losses
and Tap losses                                        Up to a max of 100m cable lengths

Output level 85 dBμV                 -24 dB
(25 dBmV)
average for Costa Blanca

What to do? Install 2 x Amplifiers/Splitters, both strategically placed by careful measurements, these should be set to increase the levels so that the Set top
Boxes see a signal level of about 66 dBμV (6 dBmV) each for continuous operation levels, this is a gain of 20 dB which is over the maximum most amplifiers
can output, but we can set them to % to reach acceptable levels (reduced noise since the amplifiers are not set to max) and the input level of each STB would
would be within a range to be workable and better.

You can see with the use of the correct cable and amplifiers working in a low noise situation the TV pictures would be acceptable under most situations.

But what happens if we have 16, 26, 50, 100, 300, 500 houses, this multi- splitter solution would not work especially if more that 50 houses needed to be
connected, very messy, logistic nightmare and severe increase in injected noise into the cable network. Not recommended.

and professionals who have been trained to high standards have the solution, and it is for houses up to 1000 +
SINGLE CABLE MULTI-USER SYSTEM ( English/German/French QAM TV system)

Remember we said that the higher the frequency the less distance it travels, so why don't we try lowering it to a point that it travels the maximum distance and
conforms to the basics (QAM) of sending TV signals down a coaxial cable.

We can lower it right down to channel S21 (302 MHz which is a vast difference to 950 MHz) however there are some 'trade offs' we are now beginning to restrict the
amount of TV channels we can view, although this is purely down to cost, since single cable multi-channels processing systems equipment costs are considerably
more than Multi-Splitter multi-cable systems.
Having said that, it is down to cost anyway, but the distinct advantage is that you can connect 100's of houses to one Satellite dish, and that in most urbanisations,
this single cable coaxial network has been already installed by the housing constructor.
Brilliant..... almost no cable costs!!
This shows 4 x Set top Boxes each 100m away from each other, and the last unit 400m away from the source, this would work OK since
dBμV                                                              dBμV     dBmV,)
the input level requirement for this type is 45 dBμV (-15 dBmV) and the level at the last Set top Box is still 78 dBμV (18 dBmV,) well above it's
minimum operating level. In fact theoretically you could attach Set top boxes up to 700 metres before the need for an amplifier,
1 every 20 metres that's 35 houses along 1 cable, install a signal splitter and add 6 more streets with a single coaxial cable and based on
Satellite dish   the calculations above you have connected over 200 houses all with a perfect digital picture and there could be 1 mile + between the end of line users.

Multi-Channel                                                                                           100m                     100m                        more
RG11 type (UG) Underground cable,                         100m
QPSK - QAM
processor            100m Average Cable loss -7 dB                            -7 dB                   -7 dB                    -7 dB
302 MHz start
Frequency
100dBμV
Output level 100dBμV
average for Costa Blanca
The limits are almost endless, but to improve on this we would begin to look at Fibre Optics..... but that is another story

Conclusion

The amplitude and quality of the signal depends on its attenuation in the cables and is directly affected by the type and the length used, and the
frequencies of the TV signals,
It is very important to use of the correct cable for each application, and above all only use installers who have professional knowledge of community TV.
Systems.

You only have to ask them a few specific questions and you will soon formulate your opinion as to their capabilities.

Those questions? Well they are in this document!
Finally, let us have a look at another standard that is frequently shipped down cable systems especially for Spanish communities.
The Spanish Technicians, some years ago must have thought of a way to use a single cable system that would transport Analogue Television to be available at
the TV wall socket, not for 1 user but the whole community.
They used, would you believe RG 11 type cable because they knew that it's characteristics was more than suitable for Television signals and to be reliable and robust,
they were not “ vaqueros” but trained technicians.
So with the advent of Digital Terrestrial TV (TDT) and we all know that this has got to be available to all community property boundaries by April 2010.

We are looking at a new standard COFDM.
This unfortunately, for transporting digital TV signals in this format poses a few problems but if we use a strategically placed amplifiers, reasonable distances can
be covered.

SINGLE CABLE MULTI-USER SYSTEM ( Spanish TV COFDM)

This shows 4 x Set top Boxes each 100m away from each other, and the last unit 400m away from the source, this would not work OK
47dBμV                                                            dBμV,
for 3 of them since the input level requirement for this type is 47dBμV (-13 dBmV) and the level at the last Set top Box is also 47dBμV,
Terrestrial Antenna         right at it's minimum operating level. Any signal level drop to the final unit could cause it's picture to break-up!
So in this scenario it would be safe to presume that only 3 units 100m apart would be acceptable.
You could of course install 1 every 20m, up to 300m and get an acceptable signal level, then use Amplifiers adjusted only to maintain levels
without introducing noise ( hence loss of quality “ Picture-breakup”) to extend the distances.
Head End                RG11 type (UG) Underground cable,                              100m                     100m                     100m                more
TDT (COFDM)
470 – 860.75 MHz          100m     Average Cable loss -10.7 dB                         -10.7 dB                   -10.7 dB           -10.7 dB
output
dBμV
Output level 90dBμV
average for Spanish TV system Head Ends

Install a signal splitter at the Head-End and add 6 more streets with a single coaxial cable, and based on the calculations above
you have connected over 90 houses all with a perfect digital picture and there could be 100's of metres + between the end of line users,
then use Amplifiers adjusted only to maintain levels without introducing noise (hence loss of quality “Picture-breakup”) to extend the distances
and add more users.. The limits are almost endless, but to improve on this we would begin to look at Fibre Optics..... but that is another story

Simple, isn't it?

Phil. BEng Electronic Engineering
Phil

Specialist in Electronic Engineering, Computer & Internet Technologies, Computer Programming (VB 6, Flash 8)
Signals, Telecoms and Communication, Engineering Mathematics, Digital Signal Processing
and Digital Media

Masters of Digital Community Television

Table showing 3 different TV standards and the cable used to transport these signals into a community TV Network

Cable TV Systems Cable characteristics

Satellite TV Multi-Splitter systems                Cable Types                             Cable Types
Modulation QPSK (SAT IF Band)           RG 6 (Standard Satellite TV cable)      RG 11 (Long Distance CATV cable)

Frequency Range 950 – 2150 MHz

Frequency of TV signal             Loss of TV signal for every 100m         Loss of TV signal for every 100m
9150 MHz                                20.83 dB                                 12.00 dB
2150 MHz                                29.50 dB                                 18.50 dB

TDT Terrestrial TV (e.g. Spanish)                  Cable Types                             Cable Types
Modulation COFDM (UHF Band)             RG 6 (Standard Satellite TV cable)      RG 11 (Long Distance CATV cable)

Frequency Range 470 – 860.75 MHz

Frequency of TV signal             Loss of TV signal for every 100m         Loss of TV signal for every 100m
470 MHz                                13.30 dB                                  8.75 dB
86.75 MHz                               18.20 dB                                 12.60 dB

Single Cable Processor Systems                     Cable Types                             Cable Types
Modulation QAM (TV Hyper Band)           RG 6 (Standard Satellite TV cable)      RG 11 (Long Distance CATV cable)

Frequency Range 302 – 444.75 MHz
( also 470 – 860.75 MHz, rarely used)

Frequency of TV signal             Loss of TV signal for every 100m         Loss of TV signal for every 100m
302 MHz                                 11.25 dB                                  7.05 dB
444.75 MHz                               13.50 dB                                  8.50 dB
Satellite Signals standard now generally use.......

QPSK [Quadrature Phase-Shift Keying] is a system of modulating digital signals onto a radio-frequency carrier signal using four phase states (four
symbols) to code two digital bits per symbol. Frequency range 950- 2150 MHz which is above the UHF band, the signals are notoriously weak but
acceptable if the receiver is within close proximity of the Satellite dish. Or for short distance cable networks.

Cable TV systems now generally use..........

QAM ( DVB-C) [Quadrature Amplitude Modulation]

QAM is digital signals which modulate both Amplitude and Phase of a radio-frequency carrier signal .
This system is widely used in Europe, Australia and America for trans-modulating the weak QPSK to QAM signals for cable TV operators, these
signals operate from the Hyperband channel S21 and through the UHF band to channel 69.
Also used for terrestrial microwaves links, MMDS and for us CATV (cable television).

Terrestrial TV systems now generally use ........

COFDM (DVB-T) [Coded Orthogonal Frequency Division Multiplexing]

COFDM often called TDT(Spain) and DTTV (UK). Used for terrestrial transmissions using existing style TV antennas since the frequencies are in
the UHF TV band. It is a single-carrier or multiple sub-carrier modulation format. The data is split into many closely spaced sub-carriers. Multiple
physical TV channels combined into one multiplexed TV channel, these range from UHF band C 21 - C 69 in Spain and C21- C68 in UK.
These TV signals can also be transported into single cables for Community TV systems

In all digital modulation schemes the carrier continuously moves on various predefined positions
of phase and/or amplitude (Symbols) (basically the digital modulation rate, called Symbol rate).

Another quality document from the professionals

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