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Go Back   SailNet Community > On Board > Gear & Maintenance > VHF Antenna install tools? and ??'s
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Thread: VHF Antenna install tools? and ??'s Reply to Thread
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Topic Review (Newest First)
03-02-2011 03:50 AM
john1066
Quote:
Originally Posted by johnnyandjebus View Post
Thanks for the details. I do have one question regarding RG8 cable. My local store sells it by the foot but it called RG8X.
Is this the same as RG8?
No. As I said earlier:
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.

Hope this helps.
03-01-2011 07:32 PM
johnnyandjebus hellosalior

Your timing is perfect on your advice, lowes just opened a store in my town, I'll be dropping by tomorrow night.

Thanks,
John
03-01-2011 07:23 PM
hellosailor John, if you use Solder-It paste (Lowes has it fresher and cheaper than Radio Shack) instead of regular solder, it is much easier to get the solder flowing into the coax shield. I'll dry-fit the connector, then apply the paste to the shield and reseat it in the connector. Now there's already solder INSIDE the fitting, so it is very easy to get it melted and filling properly.

Two drawbacks: it does cost a little more, and it goes stale (hardens) in the tube in a year or so. But it sure makes the soldering easy.
03-01-2011 06:43 PM
johnnyandjebus Again, thanks all for the replies.


SVA
Point taken on limiting the # of connections. With that said running a single cable thru the deck to the radio is problematic in my mind, having to disassemble a thru deck fitting twice a year may cause it's own set of problems.

At this point my own concern is weither to solder the connections or use fittings. I think what I may do is but several feet of cable and solder type connections and practice my soldering.

LakeSureriorGeezer.
Thanks for the details. I do have one question regarding RG8 cable. My local store sells it by the foot but it called RG8X.
Is this the same as RG8?
I will be dropping by their store this weekend to get more details

See link below for details on the cable they sell.

RG8X Coax Cable - Pride Marine - Ontario Canada

Thanks,
John
03-01-2011 09:28 AM
SVAuspicious
Quote:
Originally Posted by johnnyandjebus View Post
My thought is to use the gland with a one foot piece of cable, connectors at either end.
That is not a very good idea. Every connector causes an impendence bump and consequent loss. If you use male connectors at each end of your 1' cable, barrel connectors, and male connectors on the cables in each direction that is FOUR connections, two of which have to be completely waterproof.

Can't you just run continuous cable from the masthead to the radio? On the occasions when you do have to take out the mast you can disassemble the clam and pull the cable back from the radio to the deck. On most boats that isn't so awful.

The Dri Plug is interesting. I wish the pictures were bigger and the specs more apparent.
03-01-2011 06:36 AM
BubbleheadMd For the deck penetration, the Dri-Plug comes highly recommended. You can get one just for the coax, or you can buy one that passes mast power wiring AND the coax.

Dri-Plug
02-28-2011 10:09 PM
LakeSuperiorGeezer 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
02-28-2011 08:29 PM
fairbank56
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
02-28-2011 07:52 PM
chef2sail 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
02-28-2011 07:27 PM
johnnyandjebus 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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