Long Freeview TV aerial extension cable - use F plugs & satellite cable?

[John Stumbles]

I want to re-route our existing TV aerial cable which presently drops from the aerial on the central chimney down the roof and front of the house. Rather than try to sling the cable over the roof to hang down the back I plan to draw it into the attic and make an extension. We're in a weak signal area (Reading) which is not even suposed to be able to get Freeview (though we can - I've tried it). To keep losses down and make termination easier (than bloody BL plugs!) I'm thinking of using 'satellite' type cable (as used by NTL^H^H^HVirgin) and F plugs.

Does this seem like a good idea? And what type of cable? Some F plugs are specced to fit "PH100, PF100, RG6 and CT100" cable: what's the difference between them? Has CT100 been superseeded by H109F and WC100?

seems to have much lower prices on cables than anywhere else I've come across - anyone had any dealings with them? They suggest RG6 "for connecting additional TV sets via the RF out socket" which seems to indicate it's OK for UHF (though maybe not low-loss?)

And what about twist-on connectors versus crimp connectors, and if crimps are the bee's knees what sort of crimp tool?

tia

[Robin]

I expect someone will be along shortly who can answer on all points. In the meantime, if you have not seen it already, you might care to read Bill Wright's excellent (dare I say seminal?) article on cables

to see where RG6 stands in the rankings.

HTH

[Lobster]

Since the above will presumably involve roof work anyway, wouldn't it be possible simply to run a completely new cable from the aerial?

David

[Steve]

F plugs are far superior in every way to the old BL plugs.

As far as coax goes, you get what you pay for. Normally cheap versions have reduced braid coverage and an aluminiumised foil to make up for the lack of braiding. Good coax of this type (like proper CT100 or equiv.) has much more braid coverage and a copper foil under the braid. There are lots of cheap imitations about so beware. CT100 and the like are semi-air spaced whilst cables such as PF100 have a foam dielectric. RG6 has solid polythene dielectric, is thinner and is much more lossy but more flexible. RG6 is normally used for CCTV installations where loss is not a problem or for the situation you describe below again where loss is not so important.

Crimps are quicker and easier if you have lots to do. Electrically crimped and twist-on are identical if made correctly. So for the odd connection I would use the twist on. My crimp tool for these has a hexagonal die that deforms a circular ring to hex over the cable. Cable TV companies use a different type of crimp that only fits their cable along with special F plugs.

Steve

[John Stumbles]

I'm hoping to be able to fish it in between tiles from inside the attic. If it involved getting onto the roof I'd (a) put up a new aerial (b) get someone else to do it!

[Lurch]

On Thu, 10 May 2007 07:44:14 GMT, John Stumbles mused:

All sounds a bit DIY to me, oh, right. Well, I can see you're thinking there.

[Dave Liquorice]

Might be easier to fish it up from the eaves rather than between tiles. To do the latter you are going to have to puncture the sarking, thus creating a possible water ingress point.

Even with the eaves you'll probably need to get up to them to drill the hole and poke the cable through. Slinging a light bit of kite string on a

*small* weight over the roof (so as not to crack any tiles) and hauling the full current cable over with that might be easier.

[Dave Liquorice]

For good crimps you really need to match the connector to the cable to the crimp die/tool. The tools are not cheap, so for just a few one offs spend you money on decent cable and matching (again) twist on connectors.

[John Stumbles]

It does indeed - excellent, thanks. I've started a wiki page on it here

[Geoff Winkless]

Others have addressed this.

delivered for 100m

Geoff

[The Natural Philosopher]

Far better plan is to put a booster in the loft.

[Steve]

Very good.

Just to add that 50 Ohm cable is used, almost exclusively, in radio communications and this is its main use.

Steve

[The Natural Philosopher]

Odd. I have only ever uses 50 ohm cable around the lab. Or for Ethernet. All anteannae are fed via 75ohm cable, as this matches the natural impedance of a dipole.

[Steve]

Maybe I should have made that clearer and said commercial radio communications. 50 ohm is the industry standard.

All my aerials (yagis) were fed with 50 ohm coax 7/8" & 1/2" Heliax before I moved, but often, as you say, people do use 75 ohm for things like dipoles but rarely in the commercial world.

Steve

[The Natural Philosopher]

Ah, all now makes sense..yes for some reason 50ohm is the de-facto standard in high quality stuff. Where the cost of matching it to the antenna is trivial compared with the installation costs. It is a complete nono for domestic installations of aerials though. Without a balun etc anyway. Gets you nasty reflections and standing waves..

Once past the first amplifier..if the kit is designed for it, yep, BNC or better and 50ohm all the way..

[Steve]

Only if you are considering dipoles where the impedance will be about 73 ohm and only if that dipole is at a half wavelength or multiple thereof above average ground. Most dipoles are anything but 73 ohm in reality, depending on their surroundings. So most aerials need matching to their feeder anyway.

A lot of it is historical, dating back from WW2, as a compromise between loss, power handling and saving copper.

75 ohm cable uses less copper for a given cable diameter to achieve the same loss, because the inner conductor is thinner and the dielectric is correspondingly thicker. This makes 75 ohm cheaper to make than the equivalent 50 ohm version... all other things being equal of course.

Because of the fatter inner conductor and especially because of the "skin effect", 50 ohm cable can handle more RF power than 75 ohm of the same overall diameter for a given temperature rise. This is despite the additional current that must flow in a 50 ohm system for a given power and is all due to the increased surface area of the coax inner and with slightly less thermal insulation from the dielectric.

Once past the first amplifier, for household receiving purposes it makes little difference! In fact a properly made-off good quality F connector would probably outperform a BNC (given that both used comparable coax) which ultimately relies on friction for connection surface on both inner and outer whilst a F connector has only one friction connection.

Steve

[charles]

Most pro aerials use 50ohm. After all, there are very few simple dipoles in use and many of them are folded with a natural 300 ohm impedance.

[John Stumbles]

It's used for Ethernet too, but I was writing from the POV of TV+Sat

[John Stumbles]

Yebbut I still need a cable to get it downstairs. I'll put in a booster if I have to but not knowing if there are strong in-band signals as well as the weak wanted signals, just slinging in a booster might be a waste of money whereas spending it on decent cable seems less likely to be.

[Edster]

Would old ethernet cable be any good as a TV cable? I've got loads of that left over from when I switched to Cat5.