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dotnmarty
Joined: 03 Nov 2003 Posts: 4196 City/Region: Sammamish
State or Province: WA
C-Dory Year: 1993
C-Dory Model: 16 Angler
Vessel Name: LIZZIE II
Photos: Lizzie
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Posted: Fri Jan 19, 2007 6:22 pm Post subject: antenna splint |
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My roof mounted antenna cracked in half. I had it laying flat under the full winter cover and it cracked at the end of the roof. Can I just splint it with a 3"piece of 1/2" dia galvanized pipe or will that interfer with reception somehow? Thanks _________________ MartyP
"...we're all in the same boat..." |
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Sea Wolf
Joined: 01 Nov 2003 Posts: 8650 City/Region: Redding
State or Province: CA
C-Dory Year: 1987
C-Dory Model: 22 Cruiser
Vessel Name: Sea Wolf
Photos: Sea Wolf
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Posted: Fri Jan 19, 2007 7:42 pm Post subject: |
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Marty-
The antenna is really a metal wire or ribbon inside the fiberglass sheath that holds it up and in position. The radio "pumps' an eletric charge on the metal part, sending out signal waves. A metal sheath around it to splint it would greatly interfere with the broadcasting of the waves, depending on how long it was. A three inch plastic or wooden splint shouldn't hurt your antenna too much, however.The metal part inside the antenna should be intact for good performance, as the length is "tuned" to the range of frequencies that the radio typically broadcasts.
However, in an emergency where there is no other alternative, a shortened antenna will work over limited distances, just keep the metal part that's left from being grounded out to anything.
Be careful with the fiberglass rod. The glass fibers are sometimes exposed and can be inserted into a person's fingers and skin quite easily, causing nasty itching and pain. I have clear coated with urethane and even wrapped with tape, a fiberglass antenna that was worn to keep it from displacing it's glass shards into someone .
If you have one that frequently abrades when trailering, a section of clear plastic tube (Tygon at the hardware store) can be placed where it usually rubs to stop the abrasion and problem exposure.
Joe. _________________ Sea Wolf, C-Brat #31
Lake Shasta, California
"Most of my money I spent on boats and women. The rest I squandered'. " -Annonymous |
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dotnmarty
Joined: 03 Nov 2003 Posts: 4196 City/Region: Sammamish
State or Province: WA
C-Dory Year: 1993
C-Dory Model: 16 Angler
Vessel Name: LIZZIE II
Photos: Lizzie
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Posted: Fri Jan 19, 2007 7:48 pm Post subject: |
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Thanks for the good advice Joe. |
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tpbrady
Joined: 08 Feb 2005 Posts: 891 City/Region: Anchorage
State or Province: AK
C-Dory Year: 2005
C-Dory Model: 25 Cruiser
Vessel Name: Bidarka II
Photos: Bidarka
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Posted: Fri Jan 19, 2007 9:40 pm Post subject: |
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Joe,
You're a one man help desk. _________________ Tom
22 Cruiser Bidarka 2004-2009
25 Cruiser Bidarka II 2010-2013
38 Trawler Mia Terra 2012-2015
42 Nordic Tug 2015-
28 KingFisher 2009-2014
14 Jetcraft 2000-
17 Scanoe 1981- |
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thataway
Joined: 02 Nov 2003 Posts: 20841 City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
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Posted: Fri Jan 19, 2007 9:56 pm Post subject: |
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Don't use the metal pipe. Often 1/2" CPVC pipe is the correct size to fit over the antenna--check it out. If the antenna is too big for the CPVC then the PVC will work. Slide the pipe over the antenna and pump in some sealant (silicone will work fine).
I would not use a shortened antenna or broken wire. The radio output transisters will shut down when there is a SWR mismatch--and the output may be very low. You can either carry an "emergency antenna" or make one--but it has to be a specific length of wire to have the proper SWR. _________________ Bob Austin
Thataway
Thataway (Ex Seaweed) 2007 25 C Dory May 2018 to Oct. 2021
Thisaway 2006 22' CDory November 2011 to May 2018
Caracal 18 140 Suzuki 2007 to present
Thataway TomCat 255 150 Suzukis June 2006 thru August 2011
C Pelican; 1992, 22 Cruiser, 2002 thru 2006
Frequent Sea; 2003 C D 25, 2007 thru 2009
KA6PKB
Home port: Pensacola FL |
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mikeporterinmd
Joined: 15 Sep 2006 Posts: 645
State or Province: MD
C-Dory Year: 2002
C-Dory Model: 22 Cruiser
Vessel Name: Shelly IV
Photos: Shelly-IV
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Posted: Fri Jan 19, 2007 10:43 pm Post subject: |
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thataway wrote: | Don't use the metal pipe. Often 1/2" CPVC pipe is the correct size to fit over the antenna--check it out. If the antenna is too big for the CPVC then the PVC will work. Slide the pipe over the antenna and pump in some sealant (silicone will work fine).
I would not use a shortened antenna or broken wire. The radio output transisters will shut down when there is a SWR mismatch--and the output may be very low. You can either carry an "emergency antenna" or make one--but it has to be a specific length of wire to have the proper SWR. |
How does the connecting cable figure into the SWR? Whoever installed
my old antenna cut the wire off at about 2'. Did this damage the
radio? I'd like to know because I replace the radio and wouldn't
mind selling it, but not if it is likely to be damaged.
Mike |
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dotnmarty
Joined: 03 Nov 2003 Posts: 4196 City/Region: Sammamish
State or Province: WA
C-Dory Year: 1993
C-Dory Model: 16 Angler
Vessel Name: LIZZIE II
Photos: Lizzie
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Posted: Fri Jan 19, 2007 11:06 pm Post subject: |
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Thanks Dr. Bob, I will do that. |
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Captains Cat
Joined: 03 Nov 2003 Posts: 7313 City/Region: Cod Creek>Potomac River>Chesapeake Bay
State or Province: VA
C-Dory Year: 2005
C-Dory Model: 22 Cruiser
Vessel Name: Captain's Choice II
Photos: Captain's Cat
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Posted: Sat Jan 20, 2007 8:45 am Post subject: |
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While the connecting cable has some to do with the Standing Wave Ratio (SWR), it's not much. If the radio works (transmits/receives) on high and low power, it's not "damaged". The shutdown mentioned is a temporary thing the output circuits do to protect themselves. When the high SWR condition goes away, they're back up and running.
Charlie _________________ CHARLIE and PENNY CBRAT #100
Captain's Cat II 2005 22 Cruiser
Thataway (2006 TC255 - Sold Aug 2013)
Captain's Cat (2006 TC255 - Sold January 2012)
Captain's Kitten (1995 CD 16 Angler- Sold June 2010)
Captain's Choice (1994 CD 22 Cruiser- Sold Jun 2007)
Potomac River/Chesapeake Bay
K4KBA |
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dotnmarty
Joined: 03 Nov 2003 Posts: 4196 City/Region: Sammamish
State or Province: WA
C-Dory Year: 1993
C-Dory Model: 16 Angler
Vessel Name: LIZZIE II
Photos: Lizzie
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Posted: Sat Jan 20, 2007 10:37 am Post subject: |
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Well, thanks to your help, she's up and running. But I am worried about 'next time'. Is there a recommended 'shorter' VHF antenna that won't overhang the roof when folded down? My mount is simple and on the hand rail. I don't want to move the whole thing down and have to drill holes. Thanks again. |
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journey on
Joined: 03 Mar 2005 Posts: 3597 City/Region: Valley Centre
State or Province: CA
C-Dory Year: 2005
C-Dory Model: 25 Cruiser
Vessel Name: journey on
Photos: Journey On
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Posted: Sat Jan 20, 2007 11:57 am Post subject: |
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One can buy all lengths of VHF antennae, down to the short 3 ft. sailboat antennae. The tradeoff is gain (the taller put out twice as much electrical power: 6 dB vs 3 dB,) and height. I have a 8' plastic antenna and of course need to lay it down when we're trailering. To do it neatly, I have to remove the antenna from the mount, and then tie it to the handrails. I left enough of a service loop in the cable to be able to do this. Pain in the rear, but it works.
Boris |
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dotnmarty
Joined: 03 Nov 2003 Posts: 4196 City/Region: Sammamish
State or Province: WA
C-Dory Year: 1993
C-Dory Model: 16 Angler
Vessel Name: LIZZIE II
Photos: Lizzie
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Posted: Sat Jan 20, 2007 12:25 pm Post subject: |
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Boris-I only trailer the boat and since it is a 16 footer I'm gonna have overhang. I really don't want the extra nusiance of doing that disconnect every time. Also and probably more importantly, I don't want to poke a hole in my winter cover to avoid the stress on the fiberglass pole. I wonder how much practical difference 3db vs. 6 db gain really would make in my Puget Sound boating? Thanks |
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Alasgun Guest
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Posted: Sat Jan 20, 2007 1:25 pm Post subject: Antenna Splint |
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We have an 8 ft digital antenna , rail mounted on Huda Thunkits roof. When folded about 4 inches hangs off the back of the cabin. When trailering and when in winter storage we just slip a 6 inch piece of 3/4 pipe insulation over the antenna end. Using one of those smallest bungee cords, the one with a ball on the end, we can hold everything securely to the rail.
We are into our 2nd winter with this arrangement and it has endured numerous snow removals with out incident.
Mike on Huda Thunkit |
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dotnmarty
Joined: 03 Nov 2003 Posts: 4196 City/Region: Sammamish
State or Province: WA
C-Dory Year: 1993
C-Dory Model: 16 Angler
Vessel Name: LIZZIE II
Photos: Lizzie
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Posted: Sat Jan 20, 2007 1:33 pm Post subject: |
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Mike-Your response couldnt have come at a better time I just bought 8 feet of PVC pipe to get the 3 inches I need for a sleeve/splint. You know, between the help I get on this site and the guy at ACE hardware, I might actually build a bird house before I die. Thanks |
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thataway
Joined: 02 Nov 2003 Posts: 20841 City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
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Posted: Sat Jan 20, 2007 4:35 pm Post subject: |
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Agree that trimming down the coax to the antenna will make little if any difference in the SWR. Most antenna manufactures will say not to make the coax shorter than 3 feet. There is a little loss in Coax, but it is so little that not negiable.
For a short antenna, I used a 3 foot Metz SS whip base loaded on top of a 2 foot SS extension. This prevented the broken whips which overhung the cockpit or top.
I like the digital over the Shakespheare. I take my antenna analyzer to the store when I buy an new antenna, and find that the SWR seems slighter better on the Digital.
Bob Austin |
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dotnmarty
Joined: 03 Nov 2003 Posts: 4196 City/Region: Sammamish
State or Province: WA
C-Dory Year: 1993
C-Dory Model: 16 Angler
Vessel Name: LIZZIE II
Photos: Lizzie
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Posted: Sat Jan 20, 2007 6:48 pm Post subject: |
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thataway wrote: |
For a short antenna, I used a 3 foot Metz SS whip base loaded on top of a 2 foot SS extension. This prevented the broken whips which overhung the cockpit or top.
Bob Austin |
OK, that's good enough for me, a 3 foot Metz SS whip base etc. it will be. Thanks again. |
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