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32-3 mast antenna

Shawn Brooks

Member II
I think I have a problem with my vhf antenna and/or the cabling going to through the mast. While I can still receive AIS and VHF, I've recently discovered that satellite AIS can no longer find my vessel. Also when coming into Turks and Caicos, Radio Provo didn't seem to be able to read me until I was just a few miles away. They are typically super responsive (being part of a national SAR org) and can reach out 20 miles or more.

I haven't put eyes on the antenna yet, but I'm thinking the problem could be just a worn-out cable, antenna, connector, or all of the above. Does anyone have any experience with running new coax through the mast? Does it require taking the mast down? Anything useful to know? Any way to do some testing (aside from radio checks) to further diagnose the problem?
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
I had the coax replaced at the last re-rig, just a few years ago. The cable does indeed age from heat. I understand that, absent any physical damage, the impedance changes and the signal strength declines. I am not an engineer, tho, so others may have more learned commentary.

Back about a decade ago, I did have to have our antenna replaced by a rigger when the ss antenna detached from the little bottom loading coil, and fell down on our deck. (!) :(

Have you checked the cable exit from the spar, normally out of sight just above the headliner? There should be a coax metal connector there and it may shows effects of moisture or corrosion. From there another piece of coax should go to the panel where the radio is installed. That is my guess from observing similar installations in similar boats, anyhow.

Edit: maybe worth a passing mention is that almost all the technical/mechanical difficulties of a masthead antenna can be avoided. If... the owner decides on a location more easily accessible from the deck. The trade-off is "range anxiety" and there is indeed some reduction in transmission reach due the line-of-sight limitations of VHF. I mention this only because we got by fine for ten years with a stern rail mounted VHF antenna on our prior 26 foot sailboat.
FWIW, we could also mount a VHF antenna on a short stalk on our present boat's radar post, if we chose to.
On any boat I have been on, the most limited range was indeed found when using a handheld VHF in the cockpit, even lower in height.
 
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Shawn Brooks

Member II
I went up the mast today and the coax comes out of the top of the mast then loops around 360 degrees into the bottom of the antenna. The connector is good--the outside is grungy but the inside is clean metal. The coax, however, is brittle and the pvc cover has split in a couple of spots. I couldn't position myself well enough to see if the inner cable structure was also compromised, but I'm pretty sure it is or will be very soon. I'm convinced that a new coax is necessary and might as well get a new antenna while I'm at it.

Below deck looks good--cable is still pliable as if it were new and the connectors are it good shape.

I'm guessing the coax is run down through some sort of conduit, but I'm not sure. It could be fastened directly to the mast internally for all I know. I'm wondering if I can just cut the coax at the masthead and use it as a snake to pull a messenger line down inside the mast and follow it with a the replacement coax.

My situation is that I'm in a remote place without a lot of resources, and I could see making a bad situation (poor vhf range) worse (no vhf). I think for now I just cope and make the repair once I get back to civilization.
 

gabriel

Live free or die hard
I would have someone pull from the bottom while you hold the top and see if the cable can be pulled through. Just don’t loose the bitter end of it in the mast!

Did you uscrew the back of the connector as well? Water can seep into the back of the connector and degrade the connection while the front pin looks fine.

Also, it might be easier to run the cable from the top down, that way gravity helps you and you can make the connection between old and new cable thinner. Silicone spray.
 
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