Link below provided by, Don W7OXR
Did you ever wonder if there was a “cost” to having long lengths of extra coax? Suppose you just ran a nice long length of coax to your new J-Pole antenna. You thought it would be approximately 100 feet, but it ended up being only 50 feet. Should you just coil up the extra 50-feet of coax? Or is it worth it to purchase a second, shorter length of coax? Hm . . . Let’s see . . .
Like most things in this world, the answer is “it depends”. But an excellent source of information is the coax lost calculator here: http://www.qsl.net/co8tw/Coax_Calculator.htm might yield a useful data item. Key: it depends greatly on the type of coax (not surprisingly) and (surprise, surprise) the operating frequency! HF frequencies are pretty resilient. However at VHF and UHF frequencies, coax is very, very lossy unless you buy very expensive, low-loss coax, e.g. LMR-400.
(Share your experiences at the next club meeting! Speak up!)