Splitting a tv signal - at the aerial or in the house?

[fuzzytrifle]

I've been converting a single storey barn now for some time and have put TV coax in to each room as I've progressed with the build - trying to make everything as future proof as I can.

Planning won't allow TV aerials or satellite dishes on the exterior of the building, and as the house has open ceilings we've had to install the aerial in the garage, which is a separate building.

We're currently only living in the far end of the barn, so the coax connected from the aerial to the TV is over 70m long - roughly 30m from the garage to the barn, 34m from what will eventually be an office to the temporary lounge, then another 10m from a wall mounted socket to the TV itself. According to the freeview tuner most channels are 2/3rds strength and the cable goes to both the TV freeview and a PS3 freeview box - so that we can record one thing whilst watching another.

I'd like to have up to eight TV outlets in the house in total, although we'll only ever use two at any one time.

Do I need to use some kind of splitter in the office:

http://www.screwfix.com/p/labgear-8-way-splitter-with-powerpass-all-ports/29730

with a single 30m cable connected to the aerial in the garage, or will I have to run separate cables for each outlet back to a masthead splitter? I'm guessing that I don't need to boost the signal as it currently copes with supplying two freeview receivers.

 

[Sam Gangee]

You have to amplify the signal before it runs down a long length of cable and/or before it passes through a splitter. In other words, you must compensate for losses before they occur.

Assuming that you use WF100 cable, the losses for UHF will be around 0.15 dB per metre. The loss in a 4-way splitter will be around 10 dB.

See http://www.satcure.co.uk/tech/cablespecs.htm
and http://www.satcure.co.uk/tech/amps.htm

Dependent on your layout, you could fit a 4-way masthead amplifier with variable gain, and four long cables from there. Or you could fit a single-output masthead amplifier feeding a length of cable to a 4-ways splitter followed by more lengths of cable. Either way you should make sure you have sufficient gain available then adjust it for best results.

BTW I would have put a log-periodic aerial in the roof space and painted it to match the beams or to stand out as a piece of modern art!

 

[fuzzytrifle]

Thank you for that - running 3 additional cables through the 2" ducting sounds like a much better prospect than trying to squeeze a further 7 through it - there's already the TV, telephone, ethernet and alarm cables going through it.

BTW I would have put a log-periodic aerial in the roof space and painted it to match the beams or to stand out as a piece of modern art!

I can't get a signal anywhere in the barn (even in the few small areas of loft space that we do have) due to the type of insulation that I've used.

According to the instructions the aerial currently fitted is a yagi wideband high gain, it's about 3' long and very flimsy, which isn't an problem as it's in the loft. Similar to this one:

http://www.screwfix.com/p/labgear-t...tracking url&gclid=CJ_61eKi0LwCFQjjwgod43UAyw

My wife wanted a TV in her workshop (the other half of the garage) so I connected a second piece of coax to the existing aerial. Both TVs worked until we had some bad weather. I connected the 2nd TV up to a really old aerial that came off my in-law's caravan, which looks something like this:

http://www.screwfix.com/p/labgear-18-element-high-gain-aerial/30788

It isn't even fixed to a bracket, just propped up between the roof trusses. Both aerials seem to work fine, but after discovering that there are so many different types available I'm starting to realize that there must be one better suited to my installation.

Thanks again for your advice.

 

[Sam Gangee]

The Screwfix links just go to a login page so I can't see those aerials.
You must never connect two coaxial cables directly to one aerial as that will never provide an optimum impedance match and could even lose some channels completely.

I can't think of anything to add to my previous advice.

 

[SimonH2]

According to the instructions the aerial currently fitted is a yagi wideband high gain, it's about 3' long and very flimsy

Sounds like a bacofoil contract aerial. I suspect many installers fit them because they are cheap, will last long enough not to have to replace it under warranty, but are guaranteed to fail sooner or later and hence need replacing (for more income) Perhaps I'm being too cynical.

I'd suggest getting a good aerial. The more gain you can get from the aerial itself, the more you can lose without having to boost the signal - work on the basis that while you can have too much signal, it's far easier (and better) to be throwing it away. As a mate puts it (usually when talking about installing cabling, "better looking at it than for it").
At home when we put a new aerial up I bought a big Yagi, but the next one I buy (for G/F's house) will be the log36 as it seems we might get shifted down into group A in a few years (where the Yagi 18 C/D has naff all gain).

You haven't said where you are, which transmitter you use, or what signal strength you have. Wolfbane have an excellent signal strength predictor. If you have a reasonably strong signal, you might get away with a good aerial and passive splitters.
Note that as you might have some very long and some short runs, you may need attenuators on the shorter runs to get the signal down to what the equipment can cope with (you can have too much signal).