I would say ct100 cable or even better WF100 if you can get it.
Or HD100,
Seriously @Marc it would be benificial upgrading to CT100 or WF100 as both are double screened compared to the single braid your likely to see on R6 and RG11 coax. The cable screen in CT100 and WF100 will dramatically improve cable performance it will also improve signal losses and protect against RF, EMF interference along with RF leakage. The difference between HD100 and CT/WF is its triple screened.
CT100 and WF100 are very similar and offer the same performance. The main difference is CT100 contains a plastic air spaced dialectic insulation and WF100 is hd foam filled insulation and is harder to kink. It is also much more resitant to water ingress than the plastic honeycombe shape dialectic that can fill with water over time.
You can pick up 25m Smedz branded WF100 for £18.95 or 25m or 25m CT100 £16.00 Toolstation. If you have an aerial/satalite shop near you they will sell you Webro or Triax coax in the length you require and you would beable to ask them to crimp on waterproof F connectors, not as this matters as there are otherways listed above.
Moving on from that there is the possibility to install a mast amplifier, which is the correct way because it amplifies the signal before any signal is lost, but only in the right conditions and as a last resort. Mast amplifiers along with a booster aren’t the perfect world scenario as they will without a doubt come with trade offs. Put simply, by amplifing signal you will will make it stronger, at the same time you are likely to amplify things you don’t really want and introduce noise, interferance and the possibility of inducing signals from other Transmitters nearby. By using better coax this will limit noise and interference to some extent….
There is also the possibilty of sticking the aerial on a 10 or 12ft pole and turn the pole by means of alignment.
Any questions please ask 🙂