I asked my buddies over on the repeater builder site about coax and got about the same mixed thoughts. However I did get many very good responses. Here are 2 that I found very helpful.
Hopefully this is helpful to you. If you need the Belden pamphlet the second guy was talking about I will find it and post it. Vern I suggest using some of the practices I employed in several control and repeater stations I have installed on the Pacific Coast, subject to corrosive salt air and runoff. First off, use genuine Military Specification RG-214/U silver-plated coaxial cable, and not any ersatz cable that has the word "type" in its identification. Second, use only silver-plated type N connectors with gold-plated center pins. Crimp connectors made by RF Industries are very good, when installed with the proper tools. Waterproof all connectors with self-vulcanizing rubber splicing tape, with an over-wrap of Scotch Super 88 plastic tape. To prevent the cable from whipping back and forth inside the mast, use spacers that support the cable at regular intervals. Use marine cable entry ports that seal around the cable, wherever the cable passes from a wet to a dry environment. Make certain that the antenna base is solidly connected to the mast, and that the mast is properly grounded for lightning protection. A surge arrestor should be placed at the radio, to protect it from lightning surges. Needless to say, a boat with a metal mast tends to attract lightning, so all radio equipment should be protected. One fellow down the reply list sent you the Belden marine pamphlet, give that man a prize. The short answer is the biggest **flexible** cable you can manage. But there are other considerations just as important; 1) Supporting the weight of cable. Clamp it at the top and bottom. Don't expect the connectors to support it. 2) Make sure it's not going to thrash around inside the mast. It will destroy the finish and the mast will rot from the inside out invisibly. One way to do this is support the cable from the bottom and let it 'Pile up" lightly inside the mast. This can be tricky because you want it tight enough to avoid rubbing. On one friend's boat we cut some plastic washers that looked like big external tooth lock washers. The coax, radar control cable, and mast light power went in the center hole and the outside was deformed to hold the whole assembly in place. These were installed every two feet by pushing them in place with a piece of PVC pipe (actually several pieces daisy chained.) The external notches insured air circulation and water drainage. . 3) Make sure that all water can drain. Don't wedge the cable with a piece of foam in a way that lets water collect. 4) Tape all connections with lots of overlap. I prefer to use self vulcanizing silicon rubber tape. Done properly, your metal parts will be *bright* after 20 years of exposure. If it's exposed to UV, put two layers of Scotch 88T over the silicon stuff that gets replaced every few years. A tape source: http://www.harmancorp.com/products/hightemperaturepaintmasks/siliconetape.as px $8.80 for 12 yards X 1" Stretch it to twice it's length and wrap to cover the green center stripe. This stuff it tapered with a thick center and very thin edge. It will reliably cover and seal almost anything in one pass.
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