Hi Beswick, I've only just read your query, and whilst I would normally agree with Alan, Brian and eyeinthe sky over the use of the best co-ax (agreed Westlake is the best) available, with only 4 metres downlead length you can get away with any decent co-ax (even a HQ RG174, ie better than the standard used on the basic RB supplied antenna, with decent screening) this is thin enough to thread through a window frame and remain there. RG213 and Westlake is 10mm outside diameter and do not bend easily, being much stiffer. If you were going over 10m then heavier co-ax would be far more desirable. Bear in mind the standard supplied antenna only has 4 or 5m RG174 (od somewhat dubious quality) and look at the results achieved with that. For my money the most important thing is to get the external end of the co-ax and connections throughly water-proofed - electricians' silicone grease is great.