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  #1  
Old 02-27-2011
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VHF Antenna install tools? and ??'s

Hello all

I will be installing a VHF antenna on my boat this spring and have a couple of questions.
First off the boat is a contessa 26, deck stepped mast.

1) Where can I buy(online) a crimping tool to make the required coaxial cable connections?
2) Given that the mast is deck stepped, where can I buy a piece of hardware that will allow me to pass the coaxial cable thru the deck? West Marine has something that will work but I am looking for alternatives.


Thanks,
John
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Old 02-27-2011
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John

I would suggest you solder the coax to the PL-259 plug. Also - look up your local HAM Radio club - there are lots of old HAMs who love to help. They will even help to "tune" the antenna for you.

There are a number of ways to go through the deck. A great way to seal the connections to the elements is with a thing called Coax Seal.

I hope this helps a bit.

Rik
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Old 02-27-2011
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The best way to pass a coax connection through a deck is probably one of these:



It also allows you to easily disconnect the VHF cable that goes up the mast from the cabin top when unstepping the mast.

As for making the connections, you should probably read this page.
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Old 02-27-2011
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John, you'll probably be using something like RG58, which is actually too thin to fit standard SO239/PL259 connections. They are made for thicker RG8 coax but there are different versions to fit the thinner cable. Make sure your cable and fittings are matched!

In any case, none of those are crimped. Crimps are for cableTV and similar coax, they aren't used with VHF. You either solder, or use compression fittings. (Plenty of coaching on both online.) Either way will work if you do it right. I'd suggest you buy a couple of extra fittings and an extra foot or two of cable so you can cut it shorter & try again if the fitting isn't right.

Take the time to make good connections and buy premium cable. Stress-relieve it, use silicon grease in the fittings, use "coax wrap" or butyl or silion tape over it, to keep water out. The little things like that are going to push up your cost and double the time it takes--but they'll also double or triple the life you get out of the job.
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Old 02-28-2011
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Quote:
Originally Posted by johnnyandjebus View Post
Hello all

I will be installing a VHF antenna on my boat this spring and have a couple of questions.
First off the boat is a contessa 26, deck stepped mast.

1) Where can I buy(online) a crimping tool to make the required coaxial cable connections?
2) Given that the mast is deck stepped, where can I buy a piece of hardware that will allow me to pass the coaxial cable thru the deck? West Marine has something that will work but I am looking for alternatives.
I would suggest you use RG8X cable for the length of run you will need. It is a 6mm cable and a good compromise between the 10mm RG213 or RG8 and the 5mm RG58 which should not be used for long runs, although often is. RG58 is just too lossy to give you the performance required by, for instance, the offshore racing authorities. RG8X is OK for up to 20m or so - more than that and you need RG8 or RG213.

Your cable should be tinned and the center core should be stranded so that it is flexible. The braid coverage should exceed 90%. Berkshire and Ancor are both good.

Use PL259 connectors, solder type. Maxgain in the US produce an excellent silver plated brass connector that is excellent. With the PL259 connector you use an RG8X adapter. You can see how to fit the PL259 here:
http://www.saltyjohn.co.uk/resources...al%20cable.pdf

To go through the deck you can use a bulkhead barrel connector, as SD says, but you will have to protect it well. You can also use a deck gland that will allow the cable with connector attached to pass through. That way you don't have to cut the cable if you remove your mast. You can make a connection inside the boat, so you don't have to strip the cable out from the headlining when you drop the mast, by using two PL259's and a PL258 double female.

Hope this helps.
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Old 02-28-2011
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The bulkhead barrel connector is a particularly poor choice for through deck connection. They are difficult to seal at the through-deck point and prone to leaking water into the coax below deck, destroying the cable.

Most boats have a J-tube and a drip loop for taking wires and cables from below up the mast. Look for how your current wiring is run for anchor light and steaming light as well as any wind instruments you may have at the masthead.

In the absence of a J-tube a cable gland is a perfectly acceptable solution. There is a short discussion and a link on a previous SailNet thread: Connector for running a wire through the deck .
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Old 02-28-2011
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thanks all for the replies, a followup question.
Hellosalior mentions Stress-relieve it Can anyone expand on this?

I have not yet made up my mind weither to go with the gland deck fitting or a barrel type connection, my local marine store has both. The barrel type connection is a little different than what SD suggests in that it has a plate, about 1 inch in diameter for better deck mounting. With that said I like the idea of the gland. My thought is to use the gland with a one foot piece of cable, connectors at either end. The idea being that if I happen to step on it and damage the 1 foot cable it would be easy enough to replace. With that said I have a thru deck 4 pin electrical connection at the base of the mast that has survived 30 years with out damage so perhaps I am over thinking things a bit.

Regardless thanks for the input, I am looking forward to the snow disappearing so I can get to work.

John
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Old 02-28-2011
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The key when putting the connections on the end of the cable was patience and making sure you dont bolux up the sheath on the cable where it connects to the fittings. Work accurately, have good stripping tools, a sharp exacto knife, and a good solder gun. Soldering the connection is the best way.

The fitting SD has recoomended os a good way to do it and even though we have a keel stepped mast we have a similar disconnect between the cable to the top of the mast, and the on to the radio.

Dave
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Old 02-28-2011
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Quote:
Originally Posted by hellosailor View Post
In any case, none of those are crimped. Crimps are for cableTV and similar coax, they aren't used with VHF. You either solder, or use compression fittings.
Not so, crimp connectors are used in RF applications everywhere including the VHF marine band. I'm a pro and use them all the time. They work just as well as soldered connectors when installed properly. The problem with DIY's using them is that the crimp tools are very expensive so it's not economical for you. If you don't have experience installing the solder types, I strongly suggest you get a pro to do it. I find faulty PL-259's to be the number one problem with DIY vhf and hf antenna installations. If your going to tackle it, get the silver plated PL-259 with UG/176 reducer for rg8x or UG/175 reducer for rg58.

Eric
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Old 02-28-2011
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Cable attenuation can be expressed as the watts transmitted into the cable and the watts radiated from the antenna. We could use dB loss which is based on a log scale, but lets not be complicated. We have two basic coaxial cables under consideration, RG58 with a diameter of 5 mm (.2 inch that looks about like a quarter inch in diameter but is actually a little smaller) and RG8 with a diameter of 10 mm (.4 inch). The installation is for a VHF boating frequencies so I used the 160 megahertz (MHz) frequency for calculations. Since the distance from top of mast to deck is 31.5 feet, I used 40 feet as the length of coax cable. At the VHF frequencies there is a lot of loss of power because of what are called surface effects and dialectic loss. There is a little less dialectic loss in cable that has a foam core. When transmitting at 25 watts using RG58 coax cable, 15 watts make it up to the antenna. With RG8 cable 20 watts make it to the antenna. Of course at 5 watts transmitting power the radiated power from the antenna is 4 and 3 watts for RG8 and RG58 coax. The impedance is 50 ohm. Do not use TV cabling, adaptors, antenna, and connectors which are 75 ohm.
Here is a web site for sealing coax connectors: Waterproofing a Coax connector splice
Here is one for putting the connector to the cable: How to install a coax connector- Boating and Fishing Forum
Here is the calculator for coax cable loss: Coax Loss Calculator

Last edited by LakeSuperiorGeezer; 03-01-2011 at 06:12 AM.
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