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Old 12-10-2015, 03:57 PM   #1
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question: fiberglass VHF antenna

My sailboats always had relatively small metal antennas at the top of the mast, but my trawler has a couple large fiberglass antennas. As I understand it, after 10 years or so, the sun's UV radiation does enough damage that the antennas need to be replaced. My question is: are you replacing the antenna because the fiberglass looks awful, or because the UV radiation somehow limits the antenna's ability to transmit and receive? Also, is there some way to determine when it is replacement time?
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Old 12-10-2015, 04:19 PM   #2
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Greetings,
Mr. sbg. I suspect antennas are replaced because of the degradation of the fiberglass rather than failure to transmit or receive. I think an antennas performance is that it either works or it doesn't. Nothing in between. Mine were in pretty rough shape but a couple of coats of white paint cleaned them right up.
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Old 12-10-2015, 04:20 PM   #3
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Strictly appearance. The antenna is a wire that run inside of the fiberglass.

But... The exterior coating can degrade so much that you get itchy after touching it.
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Old 12-10-2015, 04:36 PM   #4
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Greetings,
Mr. sbg. I suspect antennas are replaced because of the degradation of the fiberglass rather than failure to transmit or receive. I think an antennas performance is that it either works or it doesn't. Nothing in between. Mine were in pretty rough shape but a couple of coats of white paint cleaned them right up.

RTF, I have somewhat similar dilemma.
During delivery of our boat by the broker, they broke both our 8' fiberglass antennas clearing a bridge (?) I did not pick up on that until they were gone so it's my loss. I was thinking of just replacing them both with Sailboat type antennas for aesthetic reasons if anything. I am aware of the loss of Gain with the shorter antennas but we have an arch above flybridge and that's where they would go, out of sight & mind. You appear a Trawler veteran, what you think ? or anyone else .. ? cheers Frank B.
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Old 12-10-2015, 04:36 PM   #5
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Strictly appearance. The antenna is a wire that run inside of the fiberglass.

But... The exterior coating can degrade so much that you get itchy after touching it.
Exactly. In addition, some corrosion around connections can degrade the signal, and to some degree corrosion goes with age. A new antenna is pretty cheap (compared to most boat things, I mean).
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Old 12-10-2015, 04:40 PM   #6
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RTF, I have somewhat similar dilemma.
During delivery of our boat by the broker, they broke both our 8' fiberglass antennas clearing a bridge (?) I did not pick up on that until they were gone so it's my loss. I was thinking of just replacing them both with Sailboat type antennas for aesthetic reasons if anything. I am aware of the loss of Gain with the shorter antennas but we have an arch above flybridge and that's where they would go, out of sight & mind. You appear a Trawler veteran, what you think ? or anyone else .. ? cheers Frank B.
As just a general statement, the longer the antenna, the better the signal. That said, most likely the little 1/4-wave antennas would serve you just fine, especially since you can put them up high.
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Old 12-10-2015, 05:52 PM   #7
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Paint w/ non-metal pigment white paint to contain the itchys
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Old 12-10-2015, 06:17 PM   #8
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Strictly appearance. The antenna is a wire that run inside of the fiberglass. .
It's a wire or a brass "element" (rod). Regardless, it's what's inside of the fiberglass tube that makes it work. You can paint the outside, just don't use paint with metal in it.

Or, buy a new one.
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Old 12-10-2015, 06:24 PM   #9
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You can paint the outside, just don't use paint with metal in it.
Uh, yeah!
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Old 12-10-2015, 06:30 PM   #10
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Can I cut about 6" off and antenna still be good .I have to lay it down just a little to get under cover .
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Old 12-10-2015, 06:58 PM   #11
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just be sure to cut it off the bottom.
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Old 12-10-2015, 07:08 PM   #12
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It's 8 ft . Think I'll just get a 6 ft .
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Old 12-10-2015, 07:48 PM   #13
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I believe the antennas are pre tuned and cutting off a section may degrade the signal. I would not mess with safety equipment.
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Old 12-10-2015, 08:00 PM   #14
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Can I cut about 6" off and antenna still be good .I have to lay it down just a little to get under cover .
Or, just use a mount like this where it's easy to reach and lay it down before docking:


Even if you don't use the radio much, you do want to maximize its range in case you ever need it in an emergency.
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Old 12-10-2015, 08:15 PM   #15
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The antenna is cut to a specific length to match the frequency of your transmitter . It can be a 1/4 wavelength,1/2, or full wavelength of that frequency range, but DON'T cut it to a convenient length or your signal can be severely degraded. If a 1/2 wavelength is too long, just get a 1/4 wavelength unit. After that, the only thing that affects your signal is the height and the connectors, (including the coax cable). Ben
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Old 12-10-2015, 08:18 PM   #16
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just be sure to cut it off the bottom.
If you cut an antenna off, it will change the optimum wavelength and the SWR. If you use an antenna tuner, it will have to correct that loss in the tuner.
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Old 12-10-2015, 08:40 PM   #17
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If you cut an antenna off, it will change the optimum wavelength and the SWR. If you use an antenna tuner, it will have to correct that loss in the tuner.
missed the sarcasm huh?
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Old 12-10-2015, 08:44 PM   #18
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Have no problem with fiberglass degradation. A "sailboat" anntennae works fine with my motor vessel.



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Old 12-10-2015, 09:25 PM   #19
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The "Sailboat"antenna has a pattern that allows it to be almost as efficient in transmitting and receiving when heeled over as it is when the boat is standing upright. The longer fibreglass antenna has a pattern that is much narrower, so is not appropriate on a sailboat.
On a powerboat, there will be a difference in signal strength between the two. The longer one will have a stronger signal.
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Old 12-10-2015, 09:49 PM   #20
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The sailboat antenna is also acceptable because it is up high. Since VHF is line of sight, higher means longer range. For example my antenna on my sailboat is 50' above the water at its base.
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