Adding aerial sockets
Overview
First I must talk a little about TV. We now had analogue and digital and a TV set to see one will not see the other. We start at Channel 21 at 471Mhz and finish at Channel 68 at 847Mhz that's 49 channels sounds a lot but every area has 6 multiplex channels and 4 or 5 analogue channels so if you are able to receive 4 transmitters you would have 5 spare channels free and even if you have only one transmitter finding a free channel by chance is 77% chance of no interference. So before trying to add Sky, VCR, DVD, Games machine signals first job it to find out which channels are free.
Most TV's will allow one to scan for programs but analogue and digital are done separate so both must be scanned and notes made. There may be channels already used by next door or something you have missed so if you get problems worth trying again.
At my house in North Wales channels 30,33,34,35,40,42,43,45,48,49,52,54,55,56,58,59,60,61,62,63,64,65,66,67,68 were all in use so DVD and Sky were tuned to the lower channels.
Next the aerial back before channel 5 all the transmitters in the country transmitted the 4 channels very close together but first with channel 5 and then with digital they have tried to fit 11 channels on a system designed for 4 and in many areas this has resulted in the frequencies being all spread out so instead of selecting a colour coded small compact aerial a large wide band aerial is required which of course has more surface area and is more affected by the wind.
Although one can boost a signal you also boost any other rubbish received so the better the signal revived by a booster the better the signal transmitted so a mast head booster works best. Where you can't do that the closer the better so loft is next best and at TV when no other option.
Mast Head
The
mast head booster comes in two parts. The amplifier is of course either in or
right next to the aerial but one of the coaxial cables will have a double use it
send the signal down and also takes power up and somewhere there will be a power
supply sending power to the booster. Often although there are maybe 4 aerial
leads leaving the booster only one takes the power up. With quad LMB's which is
the equivalent for sky however normally it needs power on each coax used.
The loft
Where
sky and terrestrial TV is used the loft box is often the preferred method. Here
the sky and terrestrial are combined and sent to main TV. Here a special box
splits the two signals then the two leads feed the sky box. From hear it goes to
main TV and back to wall socket where the combined signals are sent back on a
second coax back to the loft here they are further boosted and distributed to
the other rooms. Also with this system one can add sky remote control so the
main sky box can be controlled from other rooms.
As well as these special boxes a normal 4 or 8 way booster could be used in the loft this would increase the number of cables between loft a main TV and would not have some of the extra functions.
Local
There
are times when it is not possible to use the remote amps and the only option is
a local split at the first TV. There are passive splitters (near left) and where
there is a good signal these may work. But where the signal is low an active
(i.e. battery or mains operated) splitter (far left) is required.
General
With high frequency AC impedance becomes very important and with that impedance matching it you break apart the Y splitter above you will find resistors used to match the impedance and the cable will be 50Ω, 75Ω, 95Ω or 30Ω ribbon feeder and with TV we use 75Ω getting a multi-meter you will not measure 75Ω and you just need to accept all items will be 75Ω. But in two areas you have to be careful. First is terminating into a box. There will be instructions with each box on how much cable needs to be stripped and how it is clamped these must be followed to prevent losses. The least amount of plugs and sockets the better and bringing cable direct out of the wall into a sky box does work better than using a wall plate but the plate looks better and more convent. Sending TV and Sky signals into a booster before they go to a plate will reduce loss of signal. Coax does not like sharp bends and is hydroscopic and any brakes will tend to draw in water which in turn will affect it's impedance and so loss of signal. The longer the cable also the more loses and with three story houses so form of booster (Pre-Amp) is a must. Running any data cable near to mains cable should be avoided and one should strive in any parallel wall runs to keep at least 100mm apart.
All boosters (Pre-amps) can amplify unwanted
signals as well as those wanted and where there are any transmitters close by
then band pass filters
many
of these seem a bit odd with just short lengths of coax some are home made and
some can be bought. Picture shows a mast head type. Many of the better wall
plates include band pass filters and the same with the better pre-amps
(boosters) taxi, police, fire, ambulance, railway, CB, and radio amateurs all
transmit and there signal can cause problems with the latter they are normally
helpful and will normally try to get rid of the problem for you the circuit
diagram is from a radio amateurs web site. But the rest seem to be un-interested
in your problems. There is now available twin coax which makes running cables to
and from loft easier and cable comes with different loss characteristics all
called low loss lets face it no manufacturer is going to call their cable hi
loss. There should be a spec for all cable but I have found it seems to be often
missing.
Cable
designed for satellite use is able to carry the DC power without problem some
older cable has a problem with DC. Numbers like RG59, RG6 and PF100 refer to
cable types RG6 (according to
wikipedia) is suppose to be better for long runs than RG59 and PF100 for
satellite use yet RG6 is half the price of RG59 in some outlets which tends to
make one wonder if the reports are right way around? RG6 it seems is a
generic number where RG-59/U is a specific
type which accounts for these anomalies. Basically
the more you pay the better the cable but do make sure the connectors will fit
the cable used. RG6/U has a 1mm centre core and RG-59/U has a 0.81mm
centre core which could become an issue using F type connectors. RG11 although
still 75Ω would be hard to use with stranded centre
core even though only 20db loss against RG59B/U 25DB per 100 meters at 470 to
500Mhz. the PF100/CT100 is better at 13.5DB loss per 100 meters. Looking at the
drawing with relation to RG59B/U data from
Batt cables
| No | Name | RG59B/U | CT100 |
| 1) | Inner | conductor 1/0.584 Copper clad Steel | 1/1.0 |
| 2) | Insulation | 3.71 +/- 0.10mm Solid PE | 4.45mm |
| 3) | Braid | 16/7/0.12mm Bare Copper Wire (Coverage: Min 95%) | 5.15mm |
| 4) | Jacket | 6.20 +/- 0.15mm White/Black PVC | 6.65mm Black |
Looking
at supplies like
Screwfix they give little or no information about the cable and had it not
been for the
Maplin web site saying how PF100 is the same as CT100 I would not have found
any information. The use of
coax strippers like shown to left can make life easy and I know my son uses
one every time but I am old school and struggle with a pair of snips slowly
going around the cable and I will admit I have from time to time had a stray
strand cause a short which is far less likely using a stripper but I flinch at
£13 price tag.
Faults
Weather conditions can reduce signal mainly with Isotropic Prorogation which the
old CB's called skip. In the old days of coal fires one could sometimes see this
where hot and cold air meet the smoke goes up then fans out. This layer can
channel and reflect radio signals and will CB they went up to it channelled
along and then down but TV broadcast aerials are much higher so the signal comes
down to this layer and then reflected up so reducing signal.
Changes in broadcast can also affect reception like the switching off of the
analogue transmitters or change to
digital transmitters
which can render your receiver obsolete.
Simple faults like unplugged boosters can be surprisingly hard to find
especially power to mast head amps. Even where a power supply has been swapped
for a booster and the person has been unaware the item they removed was not a
self contained booster.
Arial lead is hydroscopic and any water in the lead will destroy it and since it
normally gets in at one end it can gradually get worse.
Birds and wind can move aerials and also corrosion can cause bad connections or
bits to even fall off. Vaseline in the connection box can reduce the problems.
An Ariel will normally show short circuit if tested with a meter but where
filters are used this can change.
Ariel types
have also changed with analogue most areas could use a banded Ariel