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Author Topic: Coaxial cable to masthead  (Read 3667 times)

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John Langford

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Coaxial cable to masthead
« on: August 03, 2012, 10:46:10 AM »

My VHF radio (ICOM) reception capacity has fallen off dramatically so I did some tests and found that the radio receiver section was fine. So it has to be the coax run to the masthead or the antenna itself. Before going to the masthead to check out the antenna and the coax connection up there. I was wondering if any owners of a MK II who have taken your mast down could tell me how the coax cable running from the radio up through the mast support post in the cabin is connected at the base of the mast to the coax cable that runs up the mast itself. Since the whip antennas are generally pretty foolproof, I am assuming that it is one of the coax cables that is the problem. If so, I assume that I have to take the mast down if the cable has become wet and needs to be replaced. Since I am not too keen to do that I am also considering installing a new antenna on the pushpit or radar mast. So any advice about successful relocations of the VHF antenna at deck level would also be welcome.

BTW, the Shakespeare radio tester I used also provided the option of testing the radio's transmit capacity. In my case the 25 watt setting only produced about 12 watts and the 5 watt setting about 2 watts. The dealer who loaned me the tester said that this is not unusual in his experience.

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John
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patrice

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Re: Coaxial cable to masthead
« Reply #1 on: August 03, 2012, 11:35:46 AM »

Hi,

Good chance it is the connection itself that is corroded.  If you have the mast deck step.
My mast site on the keel, and the connection is inside under the settee. :-)
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Patrice
1989 MKI #970
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Mike and Joanne Stimmler

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Re: Coaxial cable to masthead
« Reply #2 on: August 03, 2012, 01:10:19 PM »

Hi John,
First off, I would suggest that you keep the antenna at the masthead for best reception and range.
I think the biggest culpret is going to be the coax connectors. Check those first and repair or replace any that look suspicious. If that doesn't help and you feel that you need to replace the coax cable, you should be able use the existing cable to pull in a new one and if you don't feel comfortable doing that yourself, a rigger could certinly do that for you cheaper than pulling the mast. Also, if you replace the cable, do it in one piece without intermediate connectors but leave enough slack at the base of the mast so that if and when you ever have to pull the mast in the future, you can cut the cable and put connectors on it then. Also, you may as well replace the antenna while you're up there so you have a clean start.

Mike
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Mike and Joanne Stimmler
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Ron Hill

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Re: Coaxial cable to masthead
« Reply #3 on: August 03, 2012, 01:51:38 PM »

John : With a deck stepped mast on your MK II, you are going to have to rely on the experiences of another MK II owner that has had some VHF radio antenna problems.
BTW, all MkIIs and some of the 1986 (it was an $ option) have deck stepped masts.  All 1987 thru 1994 C34s are keel stepped.

I do agree that usually the culprit is in those PL 259 connectors. I've always favored the soldered on type.  So you may want to check those connectors/connections.

A thought
« Last Edit: August 09, 2012, 05:43:34 PM by Ron Hill »
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Jim Hardesty

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Re: Coaxial cable to masthead
« Reply #4 on: August 03, 2012, 02:44:27 PM »

John,
Your hull number is close to mine so probably the same.  Guessing that you have a deck steped mast, you have 3 connectors, one at the radio, one at the mast base (need to unstep the mast to get to it) and the one at the antenna. 
Because it's easy, I'd first check the one to the radio.  Next I'd check the antena and connector at the masthead.  I've had the antena, the stainless steel rod part, loose to the base.  And they do go bad, had to replace my antena this spring.  If that doesn't fix it I think that the mast needs to come down to check out the last connector and the wire.
One other thing that came to mind.  When I first got my boat after a long rain, the base of the mast would take days to drain.  I took the mast down that winter and made the drain slot and holes larger.  The connections inside the mast were getting wet.  The problem is fixed.
I agree that the masthead is the best place for your antena.  Unless you get a powerboat type whip antena, your fixed radio won't be much better than a hand held.
My bet would be on the masthead connection or antena.  Unless you have the draining problem, then the mastbase.
Jim
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Jim Hardesty
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John Sheehan

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Re: Coaxial cable to masthead
« Reply #5 on: August 04, 2012, 09:22:57 AM »

John,

Last year I had to change out the Shakespeare antenna on our Mk II after only three years of service.  The connectors were all fine.  A quick way to check the coax and connectors would be to have someone disconnect the antenna at the masthead and using an ohm meter check for an open circuit at the end of the coax that goes into the VHF in the cabin.  If there is anything other than an open circut you have a problem in the coax or a connector.  Then have them short across the center of the connector at the masthead and the outside of the connector and it should show a short down below at the meter with just a few ohms of resistance that is in the cable normally.

John
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John Sheehan
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Stephen Butler

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Re: Coaxial cable to masthead
« Reply #6 on: August 04, 2012, 04:40:02 PM »

When we repainted our mast and boom last summer, we had the good fortune of having a marine electronics tech stop by and inspect our mast-head vhf antenna and coax.  We had planned a total replacement of the 20+ year materials, figuring that newer meant better performance, but after some measurements, were shown that all we needed was to replace one connector, and even this was in servicable condition.  If initially installed well, and inside the mast, the system seems to survive for a very long time.
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John Langford

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Re: Coaxial cable to masthead
« Reply #7 on: August 05, 2012, 01:11:19 PM »

Thanks very much all for the many suggestions.

As owners of MK IIs indicated, there is no way to simply pull a new coax cable through from the radio because of connectors in the base of the deck steppped mast. So I will be doing the masthead and sort tests before going further. I even have a new antenna to try as well. Apropos of that, my local electronics dealer says that they have stopped selling the Shakespeare masthead antennas because of failures and now only stock GAM SS IIs made by GAM Electronics in New Hampshire. Check them out at: http://www.gamelectronicsinc.com/

I will report back after the contnuity/short tests and a poke at my existing drain holes at the mast base.
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John
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stevewitt1

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Re: Coaxial cable to masthead
« Reply #8 on: August 15, 2012, 11:43:20 AM »

I'm not an electronics Guru but on my last sailboat 31' Allmand I replaced all coax with heavy coax much like the LMR400 with soldered PL259 connectors..  I believe I used a Celwave Antenna.  With a simple Standard Horizon VHF I outperformed most everyone else over the water, with the exception of the Coast Guard.

Steve

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« Last Edit: March 07, 2013, 06:27:08 AM by stevewitt1 »
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