choosing antenna cable

[1oldbuzzard]

I am going to replace a vhf antenna on top of the mast. 43' above deck and probably 75' of cable overall. I want to replace the cable too. The old one looks like about the rg59 or rg6 size cable. its a 1979 boat and probably original. These days what cable should I buy?

Additionally, I want to install a new am/fm antenna and cable. Can i use the same kind of cable so I can order all at once?

Does the height of am/fm matter much. Should I put it up top too?

I am definatly going to run 2 cables and not use a splitter.

We Travel with the Idea That If we have no schedule, we aren't late. If we don't care where we are, we aren't lost. If we have no itinerary we're exactly where we ought to be. If we can't see it this trip, we'll see it next time.

 

[Don S/V ILLusion]

There are lots of opinions on what is the best choice based on attenuation and weight aloft. Check out any of the coax loss tables you can find doing an Internet search to compare the former. Each table will give you relative signal strength attenuation per 100 ft at various frequencies.

Consider only direct bury rated cable which will withstand the constant moisture within the mast and don't skimp on connectors which canbe the greatest problem, particularly the crimp- on variety. Unless you are either very good or very lucky, you will pinch the dielectric with that junk.

My opinion is that LMR 240 is the standard by which you should compare other options.

 

[Brian D]

Your comparison frequency will be 150 MHz. Make sure you select the attenuation at 100 ft, not 100 meters. LMR240 is about 1/4" diameter and is very good. Very low loss. RG8 is very thick and heavy, and then there is RG8X. I don't recommend RG58 unless it is milspec'd. RG58 can be very lossy.

 

[coolista]

Just saw post. As past microwave downlink designer and NASA wiring engineer, I am sure you are right to run discrete wires. The deciding issue is guaranteed dB loss in the splitter itself. Just this very week I was contemplating an efficient (low mass) guide assembly inside my hollow Al mast which would alignment of the two wires with the inside surfaces of the mast - and keep them a specific distance from the surface. This is overkill but fun to think about as I plan to replace my radios and wire. So far I am hanging a long cable in the barn for a few weeks with a small weight at the bottom until it stabilizes torsion. Over the cable I intend to slip a wire loom tube, with similar weight. When the two quit unwinding, to pull them tight while aligning the cable in the loom's center (technically impossible), then fill the loom tube with expanding foam. Sounds like a lot of trouble, but as the mast lurches about, the loom tube takes the force, and the extremely fine coaxial filaments cannot receive shock or point loads - they do not fray inside the cable's plastic cover. Forty feet of small-bore loom tube weighs little, and the foam fill is almost free. At the extreme, I can form the tube from Saran Wrap, counting on the poly-urea to be all the structure needed. My goal is to guarantee the coax remains at 100% efficiency over 40 feet of shock hazard.