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Solution for VHF Antenna cable breaking

Old 09-05-2017, 08:33 AM
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Default Solution for VHF Antenna cable breaking

Replacing the Shakespeare Galaxy 8' antenna on my Parker 2330 has become a seasonal occurrence. Basically what happens is that where the cable goes through the pilothouse top, there is a stainless cable clam/deck seal and then the antenna mount is located about 8" aft of the deck seal. Because of the low angle bend of the cable between where it comes through the top and the location of the antenna, it gradually develops a crack in the cable insulation that eventually turns into a break, which leads to radio signal degradation and then failure. This crack always occurs exactly where the cable exits the deck seal.

Mounting the antenna closer to the deck seal isn't really an option, and drilling another hole through the roof to move the deck seal closer to the antenna isn't either.

I have several questions:

1. Does anyone know of a way to protect this cable from breaking? Because it happens exactly where it exits the deck seal, putting a "chafing guard" doesn't help (it actually makes the problem worse).

2. Is there a way to replace just the cable on a Galaxy 8' antenna (at the base of the antenna). It looks like it is sealed

3. Is there a better antenna with a heavier-duty cable that might be more resistant to this problem? I am loathe to spend $300 to $500 on an antenna that will have a broken cable in 16 months...

Any other ideas?

Thanks!

Brent
Old 09-05-2017, 09:26 AM
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You would do better with a 34" long metal antenna from Digital, Shakespeare, or Metz. They have the UHF female at the bottom, and come with no cable.
I've done some field testing with the Metz against the 14' Galaxy. Results were close enough to convince me. Long VHF marine antennas are made to impress visually, but IMO, have marginal merit on a small boat.
Old 09-05-2017, 09:37 AM
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I would think you could put a length of shrink around the cable in that section that would give it some more protection. Even two layers staggered might help.
Old 09-05-2017, 09:54 AM
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I would put a little more coax length between the cable clam and the antenna. That would allow a larger radius coming out of the clam
Old 09-05-2017, 10:10 AM
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Originally Posted by km1125 View Post
...put a length of shrink around the cable in that section...
No--bad idea. Adding heat-shrink to the cable will make it stiffer; it will make it easier to break somewhere else. You want to improve the flexibility, not reduce it.
Old 09-05-2017, 10:10 AM
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Originally Posted by dons2346 View Post
I would put a little more coax length between the cable clam and the antenna. That would allow a larger radius coming out of the clam
Yes--good idea. Increase the bend radius to prevent damage to the transmission line cable.
Old 09-05-2017, 10:36 AM
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Originally Posted by dons2346 View Post
I would put a little more coax length between the cable clam and the antenna. That would allow a larger radius coming out of the clam
I had the same thought and did that on the last install - increasing the bend radius. Unfortunately it still broke right at the deck seal. It actually failed faster, and I think it was because of the extra weight of the increased length of cable bouncing up and down.
Old 09-05-2017, 10:37 AM
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Originally Posted by jhebert View Post
No--bad idea. Adding heat-shrink to the cable will make it stiffer; it will make it easier to break somewhere else. You want to improve the flexibility, not reduce it.
I considered this and had the same thought. The problem seems to be that the weight of the cable Length between the antenna and the deck seal "bounces" up and down when underway. Anywhere there is a transition from "rigid" to "flexible" (like at the exit of the deck seal) it will probably fail...
Old 09-05-2017, 10:42 AM
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Originally Posted by diver dave View Post
You would do better with a 34" long metal antenna from Digital, Shakespeare, or Metz. They have the UHF female at the bottom, and come with no cable.
I've done some field testing with the Metz against the 14' Galaxy. Results were close enough to convince me. Long VHF marine antennas are made to impress visually, but IMO, have marginal merit on a small boat.
This seems like the best option. Is the connection at the base of the antenna sufficiently weatherproof/marinized? Also, the mount that comes with the Metz appears to be designed to clamp to a handrail. How would one mount it to the top of a pilot house? (I already have a coupe of Shakespeare ratchet-type mounts).

Thanks,
Old 09-05-2017, 10:53 AM
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They sell waterproof bulkhead fittings where the cable exits straight up perpendicular to the hard top if that would help.
Old 09-05-2017, 11:00 AM
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Originally Posted by BACKTOTHESEA View Post
They sell waterproof bulkhead fittings where the cable exits straight up perpendicular to the hard top if that would help.
Like this? This is what I've got on my t-top.

https://www.wholesalemarine.com/shak...yABEgJGmvD_BwE
Old 09-05-2017, 11:09 AM
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Originally Posted by Cobia 217 View Post
Like this? This is what I've got on my t-top.

https://www.wholesalemarine.com/shak...yABEgJGmvD_BwE
Yep.
Old 09-05-2017, 11:14 AM
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Yea, I already have one of those fittings on the top. Its what I'm referring to as a "cable clam/Deck Seal" and is where the cable is breaking - right where it exits the top of the seal.
Old 09-05-2017, 11:25 AM
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Originally Posted by SBH20Man View Post
I considered this and had the same thought. The problem seems to be that the weight of the cable Length between the antenna and the deck seal "bounces" up and down when underway. Anywhere there is a transition from "rigid" to "flexible" (like at the exit of the deck seal) it will probably fail...
No, it's not a bad idea. Anytime you have mechanical stress, you reinforce the focused area and then distribute it to a larger area. That's how you solve cracking problems in the real world.
Old 09-05-2017, 12:12 PM
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Originally Posted by SBH20Man View Post
This seems like the best option. Is the connection at the base of the antenna sufficiently weatherproof/marinized? Also, the mount that comes with the Metz appears to be designed to clamp to a handrail. How would one mount it to the top of a pilot house? (I already have a coupe of Shakespeare ratchet-type mounts).

Thanks,
A few different ways. How thick is the roof? You could simply use a long UHF bulkhead coax fitting. The Metz, if you toss the metal bracket, has an O ring that will seal to a flat roof.

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removes all external coax, joints, rachets, etc.

I did exactly this for an AIS antenna on my center console.
Old 09-05-2017, 12:33 PM
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Originally Posted by diver dave View Post
A few different ways. How thick is the roof? You could simply use a long UHF bulkhead coax fitting. The Metz, if you toss the metal bracket, has an O ring that will seal to a flat roof.

Attachment 878787

removes all external coax, joints, rachets, etc.

I did exactly this for an AIS antenna on my center console.
The long UHF fitting was going to me my recommendation as well. Depending on the thickness of the hardtop this should work very well.
Old 09-05-2017, 12:43 PM
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Originally Posted by Chris@BOEmarine View Post
The long UHF fitting was going to me my recommendation as well. Depending on the thickness of the hardtop this should work very well.
Interesting idea. It creates two additional connections (one which is exposed) which I'm not crazy about, but it could clean things up nicely. The roof is 3/4" marine ply with a layer of glass over it, so I'd say overall thickness is around 1" or just a touch over that.
Old 09-05-2017, 12:48 PM
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Originally Posted by SBH20Man View Post
Interesting idea. It creates two additional connections (one which is exposed) which I'm not crazy about, but it could clean things up nicely. The roof is 3/4" marine ply with a layer of glass over it, so I'd say overall thickness is around 1" or just a touch over that.
Negative. The top "connection" is internal to the Metz and is O ring sealed.

You will use only one hex nut, and it is on the inside of the top (ceiling).
Old 09-05-2017, 01:35 PM
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Originally Posted by diver dave View Post
Negative. The top "connection" is internal to the Metz and is O ring sealed.
Roger that - so there would be:

1. Connection at the VHF radio
2. Connection at the interior bulkhead fitting
3. Connection at the exterior bulkhead fitting (direct exposure to salt spray)
4. Connection internal to the Metz

Total of four connections if I'm thinking this through correctly.

Current setup has a single connection (Galaxy cable is "hard wired" at the antenna mast).

Switching to a Metz but without the bulkhead fitting would have two connections - one at the radio and one at the internal antenna connector.

My original question about mounting had to do with the actual attachment of the antenna itself, not the wiring (but this is interesting nonetheless). It looks like the 3' base coil type antennae mount to an angled bracket - is there a way to adapt it to the typical Shakespeare ratchet mount?

Thanks for all the replies - all are super helpful.
Old 09-05-2017, 02:08 PM
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I used a PL259 bulk head fitting and it lasted for over 10 years with no issue. I put some dielectric grease lightly on the outside threads only to keep it sealed.

Jim

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