Cable Lenth vs Guage for Mast Antenna

[Terry]

After installing my antenna at the top of my M mast last summer I later read somewhere that if the cable length exceeds 30' it should be heavier guage than the standard RU32 or whatever that standard is called. I bought a 50' length (standard cheap stuff) which allows me enough extra to have the cable grommetted (so to speak) along the hatch and held in place even with the mast down and base attached to the pulpit. With the mast up I have the excess coiled near the VHF radio. I have to keep the cable held in place and out of the way so that I do not trip over it when on the deck. (yes, I know I should get a thru hull fitting and run it inside, just have't done so yet, but I would still need more than 30' and extra fittings) It did not cost very much so I can afford to remove it and buy a heavier one for transmitting over the longer length. I vaguely remember reading that the signal loses strentgh over longer cable and that one should upgrade the cable for such a length. Does this sound legitimate to anyone else?

[kmclemore]

Wow. Seems like a lot of work, coiling and stowing all that cable every time you re-mast. Plus the danger of tripping over the cable, too.

Why not just install the thru-deck plug, and then when you want to use an antenna whilst the mast is down, pick up one of these:



If you look closely you can see it suction-cupped to my mast pulpit (we were running without mast due to a serious hand injury I had in early August):

[m26roy]

I had an 8' antena on the boas and I replaced by an antena at the end of the mast. I did not took a chance and I installed the bigger coax cable RG-8X.

perfect performance.

[Paul S]

From what I understand. the length of the wire should be RG-8U, or close to it. Might be able to get away with thinner gauge wire..but since the antenna is one of the most important pieces of emergency equipment on board, I did go with the RG-8U on our 04M

Pics are here of part of the installation:

http://home.comcast.net/~testdelete/mac ... index.html

I also did purchase the emergency antenna for just in case...and for when motoring with the mast down .

Paul

[baldbaby2000]

Here is an online calculator for cable loss that might give you an idea. http://www.ocarc.ca/coax.htm. Enter 157 MHz for the frequency and select your cable. The calculator will show you the loss in dB (every 1dB is about a 20% loss) but it's easier just to look at the power lost by viewing the "power in" and "power out" fields. Notice that not all RG58 (or any other designator) cables are the same as far as loss goes. I'd say most RG58 is too lossy. RG8U is good but physically heavy. I think I'd go with RG8X as a good compromise.

There's also a chart in the West Marine catalog:

http://ecatalog.westmarine.com/0065.asp ... ckProdId=3. It shows the maximum length for a 3dB loss which is probably the worst you want. 3 dB means half your power is lost.

BB

[pokerrick1]

That Mac doesn't look bad as a powerboat with no mast!

Rick

[James V]

I had mine installed on the Mast support. Any antenna on the mast will attract lightening to your gear. Putting it on the mast support will reduce the coverage a few miles but 1 strike and you have not VHF.

Ahhh, living in Florida.

Also, If you have to travel with the mast down you still have the VHF.

[Moe]

If you don't have the new M mast support, you might also consider putting a 3' whip or 4' fiberglass antenna on a 4' extension tube on a good stainless ratchet rail mount on one of the aft pulpits. GAM Electronics makes an adapter that connects the 5/8-24 thread of the SO-239 on the bottom of whip antennas to the 1-14 thread on extensions or mounts for fiberglass antennas. It's available in either a model that brings the cable out the side, or one which continues it down through the extension and out the rail mount. This should get the antenna up over the boom and also allow the antenna/extension to be laid down for trailering.

--
Moe