Coaxial Cable Splitting

[nivrip]

A question which some may think a little dumb, but I have to know, and I'm sure there are people on this forum who can advise.

I've used a coaxial cable splitter to get the TV signal to two TVs. The splitter sits directly under the aerial in my loft. The two cables from the splitter are of different diameters but travel about the same distance to their respective TVs.

The TV served by the larger diameter cable seems perfect, in that it picks up all the signals from all the channels and works perfectly. The other TV served by the narrower diameter cable is a nightmare in that it will not pick up all the channels, frequently pixelates or simply has No Signal.

I've tried switching things around and even used a different splitter and the second TV seems fine when tuned from another separate aerial. My question is this. When a signal is split does it matter that the two outgoing cables are different (diameters) and would the signal be preferentially sent along the fatter cable?

My own feeling is that it shouldn't make any difference but can someone reassure me on this point. I feel that I may have to replace the cable to the second TV (? same diameter as the first) but it will be fiddly as it's an awkward route.

 

[muckshifter]

you will gate a better water flow in a larger diameter pipe.

Signals, via a wire, even just electricity, will meet with less resistance through a bigger core cable.

What is the signal strength on input, and what is the dB loss on the output side of the splitter, how long is the cable (you loose signal per 100tf), are there any copper piping the cables pass by? AND how old are the TVs.

 

[floppybootstomp]

Splitting a TV signal in two will weaken the signal. It looks as though the stronger of the two resulting signals is taking the path of least resistance and hogging the big cable leaving what's left of the signal to traverse the smaller cable.

The two most common types of coaxial cable differ by their impedances and are respectively 50 ohm & 75ohm. 75 ohm is used for video (TV) signals and 50 ohm is used for radio and data signals, commonly CB radio, mini cab firms and emergency services use 50ohm cable in their systems. If the thinner cable here is 50ohm that will degrade the signal.

However, unless a TV signal is at full strength then splitting it will require some amplification for distribution. Aerial amplifiers are cheap but they will need a permanent mains connection for powering. By far your best option is to fit an aerial amplifier, plug in the aerial lead and then plug both your existing signal cables into it.

I'd imagine this would be a lot less bother than replacing the thin coax cable even if it means taking a mains supply to the aerial amplifier.

The mains supply ideally should form part of a loop from one of the ring main circuits, 2.5mm T & E cable; 2nd best choice would be a spur from a ring mains cable. Third best and which is against the EEC installation rules, would be to spur off of an existing lighting circuit. This would be perfectly safe as a typical domestic aerial amplifier draws very little current.

If you have a mains socket in the attic you could run an extension cable from there to the amplifier location. It would be best to mount the amplifier on a wall or maybe one of the joists, most amplifiers will come with a mounting bracket for this.

Aerial amplifiers can be obtained from RS; Farnell; CPC; Maplins, B & Q; Wickes, Amazon and Ebay.

Good luck.

 

[nivrip]

Thanks for the replies, fellas.

I double checked the TV by trying to tune in a different one on the same aerial cable but get the same very poor signals so it's not the TV.

Mucks - no idea what the signal strength is or the dB loss either. The only info on the splitter is 5-1000 MHz. The fatter cable is about 20ft long and the thinner one is definitely longer at about 25ft.No copper pipes nearby. Fatter cable TV is about 3 years old and the other is about 2 years old.

Flops - I like your suggestion of an amplifier. It should be straight forward as there is a mains socket in the loft. With amplification will I get full strength signal down both cables? (or at least enough signal to make it work)

 

[floppybootstomp]

With amplification will I get full strength signal down both cables? (or at least enough signal to make it work)

As you have one good signal already and assuming the thinner cable has been proved good by working by itself then I'll stick my neck out and say yes.

I have a communal roof aerial here and use a three way distribution amplifier to feed all three sockets that I use (two of which I installed myself) and the signals are strong even when all three are in use simultaneously.

 

[nivrip]

Barking up the wrong tree I think it's called.

Whilst considering getting an amplifier I bumped into an old friend in the pub who is an electrical engineer and considered to be a bit of an expert on telecoms matters. I told him the story and he said that there was no way I would need an amplifier. This is simply because my TV transmitter at Bilsdale is less than 15 miles from my house and is clearly visible, not only at night when it's illuminated, but even in the daytime. Bilsdale Moor is over 1000 ft high and the mast itself is also another 1000+ ft.

He told me that he uses a splitter and, like me, has a fat and a thin cable coming from it and he has no problems whatsoever. He suggested that it could be the thinner cable that was at fault and that I should check that the outer copper shield was correctly attached to the two coaxial plugs.

When I looked at the plug to the TV I found that, sure enough, the copper shielding was not attached correctly and when rectified I got a perfect picture and all known channels.

I should have remembered to always check the basics before looking for more complicated problems.

Lesson learned, I hope.

 

[floppybootstomp]

Glad to see you got it sorted, and sorted economically as well.

Had I been 'on site' the first thing I would have done would be to check the integrity of the cables. Having only the info supplied here I assumed both cables were ok. I was also unaware of how close the transmitter was.

Still, sometimes one can overlook the obvious, me bad, think I'll hush up in future