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Old 18-11-2016, 08:22   #1
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pirate VHF Antenna and Wiring

On my 1983 Catalina 38, I would like to replace the VHF antenna and all the wiring for the antenna that goes from the unit to the masthead. With the mast in my backyard I looked at the wire as it enters the base of the mast and noticed a loop and splice of some sort? All in the same single wire? What would be a reason for boatyard to place a loop and splice? And when I get new wire and antenna, any recommendations on the best ones to use? And will I need to attach the ends after running the wire up thru the conduit? Any special tools required for that? Any advice on this project is appreciated!
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Old 18-11-2016, 08:37   #2
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Re: VHF Antenna and Wiring

The loop was likely to leave extra coax in case either end needed to be replaced. This is typical. Are you sure there is a splice? That is not typical. You shouldn't splice coax together. You could put connectors and a female to female connector in between, but that also isn't something you normally want to do. You want a single run of coax from the radio to the antenna with a male PL259 on each end.

You have two choices for your connects...solder on or crimp on. Search the forum here and you'll get more info. I prefer solder, and since you've got the mast down that should be an easy job.

As for coax, you're at VHF (around 156 MHz) so you don't need to buy high-end coax. Here's an attenuation chart. RG58 would work, RG8X is better, and RG213 is probably the best you'd ever want to go with. RG8X is a good price/quality coax to use.

Youtube is a great resource for learning to put on connectors.
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Old 18-11-2016, 08:48   #3
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Re: VHF Antenna and Wiring

Universal Radio sells all the connectors and cables you will need to replace your cable.

PL259 and SO239 Connectors

Coaxial Cable by the foot

LMR-400 is the "best" cable in terms of performance. RG8X is about 3 times more lossy than LMR-400. The price for performance is of course cost. LMR-400 is about 3 times the price of RG8X.

Universal Radio or a local ham shop can help you choose the right connectors for the cable that you select.

Often times a "splice" will be done using 2 connectors and a female barrel to join them. This is done so the mast can be removed without removing the cable from the mast to the radio. There is almost no loss in this type of "splice" as long as no water gets into it. So usually it is covered in lots of rubbery tape to keep the water out.

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Old 18-11-2016, 08:49   #4
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Re: VHF Antenna and Wiring

Is the coax likely to be original? If so rip it all out and start again. 30 year old coax isn't good news if you want good comms. MB given some good advice on specs.
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Old 18-11-2016, 09:12   #5
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Re: VHF Antenna and Wiring

Thanks, appreciate all the good info!
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Old 18-11-2016, 09:25   #6
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Re: VHF Antenna and Wiring

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Originally Posted by mdbrown View Post
As for coax, you're at VHF (around 156 MHz) so you don't need to buy high-end coax. Here's an attenuation chart. RG58 would work, RG8X is better, and RG213 is probably the best you'd ever want to go with. RG8X is a good price/quality coax to use.
I would suggest that you *not* use RG58. You probably have about 50 ft of coax, and RG58 will lose about half of your signal (-3dB). You should use one of the better cables suggested.

Is that a splice, or is it a connector union (plug / barrel / plug) taped over? It's better to avoid extra connectors, but if that makes the job easier go ahead and do it. You won't lose more than a small fraction of a dB if you use good connectors and technique. Make sure to completely seal the connectors from water.

As for connectors and soldering, since you are a novice, either get a pro to do the soldering, or plan on spending some time practicing and ruining some connectors / cable. You will need the proper tools, in particular a big soldering iron. Correctly crimped connectors are almost as good as well-soldered ones. The insulation-piercing (vampire) connectors are generally not too reliable.
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Old 18-11-2016, 10:18   #7
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VHF Antenna and Wiring

While it's not ideal to have a splice, it does help if you need to remove the mast in the future. We have a splice in our lmr-400 and it didn't effect our vhf reception or transmission at all.
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Old 18-11-2016, 10:46   #8
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Re: VHF Antenna and Wiring

The myth that loss exists in connections is false.
There are a myriad of studies measuring loss through multiple coax connectors showing essentially zero loss. The key to achieving minimal loss is to use good quality silver plated PL 259 connectors and similar barrel connectors where disconnects are needed typically at the mast step and properly soldering them to low loss, direct bury rated coax such as the LMR brand.
Crimping is the lazy way of doing it and more often than not, results in pinched coax, damage to the dielectric and shorts.
There are numerous how-to's on YouTube if anyone doesn't know the proper method.
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Old 18-11-2016, 10:48   #9
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Re: VHF Antenna and Wiring

Lmr400 is good stuff but it is thicker. If you've got room then use it. Also forgot to tell you that depending on the size of the coax you use, you may need a reducer when putting on the pl259. Send along any questions you have...plenty of people on here have done this task before. I commend you for taking it on instead of calling out a radio repair guy!
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Old 18-11-2016, 10:52   #10
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Re: VHF Antenna and Wiring

Go for the thickest and best quality marine grade coax you can fit.

Recently used DX engineering to build an 83' LM400 VHF masthead coax. They shipped it in 3 days to replace the coax damaged when the mast was pulled.

The 83' ran all way from the masthead to our chart table mounted Icom VHF. Loop at the top and all exposed cable and fittings were wrapped against UV exposure. Also used the new stainless steel scan strut cable clams. Avoid unnecessary connections and you'll minimize transmission losses.

The 83' is a pain to route all the way to the chartable when pulling the mast. I'll always take inconvenience over transmission losses.

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Old 18-11-2016, 13:58   #11
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Re: VHF Antenna and Wiring

Quote:
Originally Posted by mdbrown View Post
.........plenty of people on here have done this task before. I commend you for taking it on instead of calling out a radio repair guy!
It's a safety issue so having a pro do it makes sense for someone without the tools and skills to do it correctly.

The test may come when you are 40 miles at sea with an emergency.
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Old 18-11-2016, 13:58   #12
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Re: VHF Antenna and Wiring

Old myths die hard. Properly installed connectors create no loss. PM me if anyone wants to see evidence
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Old 18-11-2016, 14:51   #13
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Re: VHF Antenna and Wiring

Well said from the start. The central point is that if you use good coax and make good connections marine VHF radios are just about idiot proof. At the top of the mast you're using a 3dB antenna (short) that flattens the signal less than a 6dB (long) antenna, but you've got the advantage of the antenna being at mast top for longer line of sight. Nothing like playing the same game with a marine HF radio.
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Old 18-11-2016, 15:03   #14
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Re: VHF Antenna and Wiring

Hey. I did manage to get a marine VHF to fail once. It would receive but not transmit, even to a portable on the boat. I searched everything, even bringing down the radar/antenna/lights mast and checking for grounds/faults. Nothing. Technician couldn't solve it. Hopped on my bike and rode to the marine supply in wherever we were. Replaced both radio and antenna. No luck. Second technician couldn't figure it out, either, but called a friend who gave him the necessary clue. Turns out I was storing our sat phone on top of the VHF where it protruded from the slanted instrument panel. The battery charger in the sat phone was blanking the transmissions....
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Old 18-11-2016, 15:12   #15
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Re: VHF Antenna and Wiring

You may find this interesting,
Easy VHF Connections Photo Gallery by Compass Marine How To at pbase.com
Whether you have a joint at mast base will depend on how often you unstep your mast,for me its every winter,also,if your mast is thru deck,as it is being pulled you may need to pull the cable into the mast underneath to prevent it getting pinched.
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