Satellite cable.

While I'm sure you're not planning to use 50m in one run, nor even two runs of 25m, (or I certainly hope not) for anything more than about 10m I'd suggest you forget about RG6 and instead look for WF100. 

It's all about the attenuation, or in plain English losses, which to one degree or another all cables are subject to with (on paper at least) RG6 typically exhibiting twice the loss of WF100 for any given length.

In the most simplistic terms what that means is that a 1.8m dish with 30m of RG6 may actually provide no more signal than a 1.4m dish with the same length of WF100!

Matters are further compicated by the fact that RG6 and WF100 have become  generic names which refer more to their physical dimensions than actual performances. 

Needless to say there are good and bad of both types on general sale so despite the paper advantage of WF100 a length of 'good' RG6 might well out perform a similar length of 'bad' WF100! 

The proper way to select a cable then is to look at it's actual specifications and choose the one with the lowest losses AT SATELLITE FREQUENCIES typically expressed in dB/100m. 

Unsurprisingly the quality of a cable will usually be reflected in it's price which, except for the shortest of runs, pretty much rules out those to be found in the China Mercas. If the dish is in an inaccessible location then it becomes even more important to use the best cable you can afford because anything saved by skimping will very quickly be lost when you have to call somebody in to replace it!

Probably the best source is a reputable local satellite installer.

Thanks for the information. I'm no satellite engineer but even I was surprised the previous owner of the house used a very long cable. He worked in the forces in telecoms! The existing cable is Rg6 which was installed prior to us moving in. It is at least 40m long and has worked well for at least 4 years. We are now losing channels in the main house. In our casita where the cable is about 5m in length, the system works perfectly well. Soo, I'm guessing the long cable has become an issue. It is worse in hot or damp weather. My first thought was to replace the cable even at that 40m length as it has been fine, then look at other potential issues. Perhaps a rethink is needed on how we receive UK TV. The dish is a long way from the house. 

I just purchased this from Amazon

https://www.amazon.es/gp/product/B00FRVX6T4/ref=ppx_yo_dt_b_asin_title_o00_s01?ie=UTF8&psc=1&tag=cstareg0f-21

Much better quality than the cable you get from the Chinese shop.

Installed 30 mtrs for the tv outdoors. Perfect picture HD

Hope this helps

Regards

John

Thank you. I'll give it a go. 

I have got some from Ferri's in Villena.  They have small coils in the shop but of you ask they will cut whatever length you want from a reel round the back.

I seems to work OK and my dish is a long way from the house too.

Thank you.