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 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

Mast Head AmpThe 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

Loft Box BMPWhere 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.Loft Box JPG

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

Active-AmpT-SplitterWall SocketsThere 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.

F-PlugCoaxial Plug

The are many types of wall socket with both F type on right or standard TV as on left. I do find the standard type a tad of a fiddle and tend to use adaptors with F type which are easy to fit. The coax cable by the drum is quite cheap and often better getting drum than a length.

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 300Ω 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 Band Passmhf_masthead_filtersmany 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. coaxCable 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 75 Ω 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/UCT100
1) Inner conductor 1/0.584 Copper clad Steel 1/1.0
2) Insulation 3.71 +/- 0.10mm Solid PE4.45mm
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

The PF100 will have a foil as well. Again the slight difference in thickness could affect the use of F type connectors and getting cable and connectors from same supplier would be prudent. Coax-stripperLooking 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.

 

Return to main page