Things I did not know about co-axial cable

[catalac08]

Issues at home with poor tv signal and I found that the co-ax cable from chimney mounted aerial was badly corroded in the copper stranded shield, the cellophane coated with aluminium was just down to powder and the outer plastic was so brittleit just came apart by pulling at it with the fingers. On reading about co-axial cable I was amazed to read that it only has a life of 5 years outdoors, before corrosion and degradation and loss of signal takes place.

It is not something I had given any thought to previously but I assumed that it lasted pretty indefinitely. I had planned to replace the boat aerial at the masthead over winter (poor reception and even poorer transmission) but it seems to me know that the cable should also be replaced, at 39 yars old I suppose it had done it's time even though only the top few feet is out of the mast.

 

[lw395]

It can last much longer than that, or a very short time.
You don't need much oxide/corrosion on the braid, or water in the dielectric to put the loss up dramatically.
It's worth using connectors that keep the water out and fitting them carefully.
UV will attack the sheath, but you can cover the small length out of the mast in heatshrink or self amalgamating tape, or even insulating tape and re-do it every couple of years.

Living somewhere salty, the TV coax can have a short life, the aerials don't seal the cable at all well. A smear of silicone grease seems to help.

 

[elton]

I've found coax cable with the shielding completely oxidised to a light green powder.

I rented a house with the rooftop aerial cable, continuously but slowly dripping rainwater down the back of the telly!

 

[rob2]

Just a precautionary note - your TV cable must be 75 ohm, whereas the boat's VHF aerial requires 50 ohm.

Rob.

 

[ctva]

A treasure trove of information (not geeky) is here...

http://www.aerialsandtv.com/cableandleads.html

 

[prv]

I had planned to replace the boat aerial at the masthead over winter (poor reception and even poorer transmission) but it seems to me know that the cable should also be replaced

Errm - YES!

Your radio problems are probably just as much cable trouble as aerial, quite possibly more. The cable run is a very important part of the system.

There is quite a range of cable quality out there; it's worth choosing the right one rather than whatever the chandler has on his single spool in the shop (probably far too lossy for a 20m run to the top of a yacht mast).

Salty John has some useful information: http://www.saltyjohn.co.uk/resources/Marine VHF Antennas aerials and their installation.pdf

Pete

 

[mlines]

It depends on the material used to make the co-ax cable. UV stable and UV resistant versions are available with much longer life (and, of course, higher cost)

 

[NickRobinson]

I've found coax cable with the shielding completely oxidised to a light green powder.

I rented a house with the rooftop aerial cable, continuously but slowly dripping rainwater down the back of the telly!

Same drip with my GF's TV feed. As it still worked the freeview stuff, I broke the cable at the lowest point and fitted a M/F/M inline connector to drain it before the rather nice TV

 

[Ruffles]

Lime mortar and a damp wall will eat through the braid on cheap TV aerial cable in no time.

I replaced my pushpit light cable some years ago. It did occur to me at the time that as the cable is only exposed in three places and only for a few inches that some kind of UV resistant sheath would be a great idea. The same would apply to VHF coax. But I couldn't find anything. I know PVC sleeving is available - I think I have some knocking around from when I was an engineer. No idea if it's any better than the cable.

 

[catalac08]

A treasure trove of information (not geeky) is here...

http://www.aerialsandtv.com/cableandleads.html

Thanks for this link it is amazingly detailed and surely good for understanding all sorts of tv/radio/vhf problem, and hopefully resolving them. Just good entertaining reading as well. I love the "rogues gallery" of poor installations, bad fitting and things that could never possibly work.

It seems that something else I did not know is that the modern 4G mobile masts can interfer with tv and some modern tv aerials now have filters built into them to stop this. Also the older signal strength meters can be totally confused by the 4G signals and give all sort of strange readings more related to the 4G signals than Tv signals.
Amazing the things I do not know!