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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 02-11-2008
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Coax Replacement

I have a 1981 C 30 and think it is past due for a coax replacement. I have tried to determine the best method for removal of the old coax and replacement with new. The existing coax appears to be secured in some way inside the mast and I cant determine how. Has anyone done this. Can you describe what proceedures you used and any difficulties or suggestions.

Thanks in advance for any and all advice.
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George,

Depending on how the old coax was secured inside the mast, it may be very difficult or impossible to remove it without major surgery, involving removing all mast wiring.

On a 30-footer, I'd think about simply running new coax and leaving the old coax in place. Use RG-8X which has less loss at VHF frequencies than RG-58 (or a more exotic even lower loss coax if you wanna spend money).

If there is no wiring channel inside the mast through which you can pass the new coax, you'll have to come up with some means of keeping it from slapping about inside the mast (which can be both annoying and damaging to the coax over time). Some folks have had success in simply using plastic wire ties arranged in threes (grouped and at 120-degree angles to one another) every few feet. These can be compressed and pulled into the mast, where they'll open and serve as standoffs for the coax.

Bill
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Old 02-12-2008
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I read an article not too laong ago about this very thing but I can't remember what magazine it came from.
The general idea was that you run the coax and any wires INSIDE of a piece of polypropolene rope ( the yellow stuff ) and secure the rope at the top and bottom of the mast. This prevents chaffing of the wire. Also use the zip tie idea to keep things from slapping around inside the mast.
Looked like a little bit of work but the finished product was nice.
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Quote:
Originally Posted by btrayfors View Post
George,

..... Use RG-8X which has less loss at VHF frequencies than RG-58 (or a more exotic even lower loss coax if you wanna spend money).....Bill
Any idea how much of impact would the loss in signal strength be between RG8X and RG58 ?
I'm also planning to replace my coax and is toying between these two cable type. The thickness of RG8X will be a pain to run within the mast cable channel. I'm attempted to go with RG58 (high quality Belden cable - US made?).
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What makes you think your coax is bad? Have you tested it or is there a physical problem?

The issue with coaxial cable loss is a function of cable length, cable characteristics, SWR, and operating frequency. With the length required for a C-30 being less than 50', I would worry more about using a quality coax, protecting the weather end from water intrusion, and minimizing SWR if possible.

I've operated the world on ham radio SSB and CW at 5 watts with RG 58 into a 40 meter dipole, so far out of frequency the SWR was through the roof. The line loss was high but it was matched with a transmatch and worked good enough. I'm not suggesting this for VHF operation but I don't think it will be required to use a large diameter low loss coax for a short run at about 150-160 mHz.

For specifics on coax loss look here:
http://www.timesmicrowave.com/cgi-bin/calculate.pl
http://www.ac6v.com/techref.htm#coax
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Old 02-12-2008
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Thanks for the advice. I was having a real problem removing the existing coax.

mrjogrers

With the coax most likely 20 + years old I felt it prudent to consider replacing it even though I have not had any problems. Is this the type of equipment that dosent degrade just as a matter of age? If so I could be better off with if it aint broke, dont fix it???

Thanks

George
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George,

1. Replace the coax.

2. Use RG-8X marine coax. It is only a tiny bit more expensive than RG-58, and is just about the same diameter...a tiny fraction larger. Note that this is NOT the same larger diameter as RG-8 or RG-213.

Here's a good source for the coax: http://www.therfc.com/

What you want is RG-8X marine (C8X) @ $ 0.38 per foot.

You also want good quality UHF connectors (PL-259) with reducers (UG-176/AG) for RG-8X coax. Amphenol's are good; I've found the imported silver ones they carry to be of high quality, too. It's worth a call to ask them about the current best connectors, since all connectors are NOT created equal.

Bill

Last edited by btrayfors; 02-12-2008 at 01:39 PM.
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Old 02-13-2008
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George,
I'm not as familiar with marine grade coax. That being said, yes coax degrades with age, some slower than others. On one hand if it ain't broke don't fix it sounds good. On the other hand if you may need to rely on the VHF for safety replacing it could be a good idea.

Use high quality cable like btrayfors suggested, and pay attention to the end connectors. I use a 100 watt soldering iron that has a lot of mass to solder them on. Don't use the pistol shaped sldering guns, they get too hot and don't have enough mass to transfer the heat effectively. Seal the mast head end with proper coax sealer. If your library has it, you can look at the ARRL Antenna Book for some good info.

I wouldn't worry about thick, low loss cable. Just use a high quality coax that fits. Connecting and sealing the ends is extremely important. Pay attention to what the connectors are. PL259 most likely, but N connectors are much more waterproof and it is possible to have these on the outside run.
Michael
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Old 02-13-2008
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Thanks to all for the great advice. Makes it easier to do it right the first time and have it work!
George
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sv "New Perspective" C-30

"Nothing on land prepares you for the scale of the Sea.
It's principle dimensions lie beyond the muscle of language to gather it in."
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