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Old 19-03-2013, 11:01   #1
Guy
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can you combine 2 coax cables?

Hard to believe but we have 2 RG-58 cables from the mast head into the cabin. The signal loss just using 1 cable is pretty high. We usually have one of the weaker VHF radios in an anchorage. Can I splice the 2 coax cables together at either end and have a lower signal loss with the combined cables?
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Old 19-03-2013, 11:10   #2
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Re: can you combine 2 coax cables?

Nope, doesn't work that way.
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Old 19-03-2013, 11:24   #3
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Re: can you combine 2 coax cables?

I think deck officer is right, but..... each cable has it's own resistance.. and two resistances in parallel halves the resistance...hmmm.... what's wrong with this thinking...?
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Old 19-03-2013, 11:26   #4
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Re: can you combine 2 coax cables?

Nope. RF signal lose is not just cable resistance in ohms. The cable at high frequencies has a property called charactoristic impeadance that must be matched and the loss is due to other factors; not resistance. Paralleling cables would actually spoil the transfer of signal between antenna and radio.
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Old 19-03-2013, 11:33   #5
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Re: can you combine 2 coax cables?

You have more trouble than this (I say this from experience with your situation with probably 100 boats) and there is only one way out:

- remove antenna, it's mount and both old cables
- use one of the old cables to get a messenger line in there.
- install brand new antenna
- pull a brand new RG-8X antenna cable
- have a pro or a good HAM solder new connectors to the new cable.

It'll be good then

p.s. forget anything else like combining etc.

Quote:
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Hard to believe but we have 2 RG-58 cables from the mast head into the cabin. The signal loss just using 1 cable is pretty high. We usually have one of the weaker VHF radios in an anchorage. Can I splice the 2 coax cables together at either end and have a lower signal loss with the combined cables?
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Old 19-03-2013, 14:25   #6
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Re: can you combine 2 coax cables?

I would have to take the mast down to change the coax, no question about that. How about an amp? I could have 12 volts at the mast head or down below perhaps.
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Old 19-03-2013, 14:45   #7
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Re: can you combine 2 coax cables?

Well do the easy stuff first. Inspect all connections for corrosion and good soldering, the PL-259's both at the antenna and radio and any barrel connectors, SO-239 at antenna. Hope you find the cure at this point but if not, are you sure you can't use one of those old coax to pull new coax through?
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Old 19-03-2013, 14:51   #8
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Re: can you combine 2 coax cables?

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I would have to take the mast down to change the coax, no question about that. How about an amp? I could have 12 volts at the mast head or down below perhaps.
You got the info about how to do it, there isn't another way. I did manage to change my cables without taking the masts down... my masts haven't been down in the 20 years that they exist.
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Old 19-03-2013, 14:53   #9
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Re: can you combine 2 coax cables?

Quote:
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I would have to take the mast down to change the coax, no question about that. How about an amp? I could have 12 volts at the mast head or down below perhaps.
... nope.

There's a slim chance that you might have a small problem - eg some bad splice or connector - which could be the biggest issue, but it is as the Jedi teaches us... once you've gone to all the effort to troubleshoot, you might as well just have replaced the whole antenna coax run.

If you can find a skinny fearless tech who will go up in a bosun's chair, the job might be doable without dropping the mast.
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Old 19-03-2013, 15:13   #10
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Re: can you combine 2 coax cables?

My stories are often not what the OP wants to hear but that is because I've been there myself too often

The thing is that even when you find a bad connection (and I am sure every connection is bad), you would need to buy a new connector. While trying to solder that onto the old cable, you will find that the old cable doesn't want to be soldered anymore. When you take that in consideration and also the little cost of new components, it's better to just rip it out and replace.

I would be willing to put a bet on that either the center conductor or the shield of the radio's connector has no connection at all with the antenna. I have found everything imaginable, from cables just stuck into connectors without soldering (duh... must that be soldered then? ) to unconnected & removed outer braids (duh.. they told me to only connect it at one end ) or (duh... it's only for protecting the inner core so no need for it inside the connectors ) to connectors so badly corroded that the center pin was missing.

cheers,
Nick.

Quote:
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... nope.

There's a slim chance that you might have a small problem - eg some bad splice or connector - which could be the biggest issue, but it is as the Jedi teaches us... once you've gone to all the effort to troubleshoot, you might as well just have replaced the whole antenna coax run.

If you can find a skinny fearless tech who will go up in a bosun's chair, the job might be doable without dropping the mast.
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Old 19-03-2013, 15:43   #11
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Re: can you combine 2 coax cables?

Not to mention when connections aren't dressed properly, coax has the nasty habit of wicking into it a lot of salty moisture.
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Old 19-03-2013, 18:27   #12
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Re: can you combine 2 coax cables?

You-all are very encourging but I am the fool who put the RG-58 in the mast in the first place and I know about how many ty-raps I installed, One about every 8 inches along the entire run. If I can offer an excuse, along with the cable size, as an aircraft mechanic this is how you would do it in an airplane. I guess that was wrong thinking.
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Old 19-03-2013, 18:41   #13
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Re: can you combine 2 coax cables?

Old boats and old masts used to just attach the cable on the outside of the mast. You could do it that way until you drop your mast. The other way would be to put a guy on the top of the mast and drop a weighted skinny messenger down (whole new cable) and see how that goes.
kind regards,
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Old 19-03-2013, 19:40   #14
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Re: can you combine 2 coax cables?

Guy, marine VHFs are pretty much mature technology by now. A "conventional" installation, done properly, is the way to go. That means your antenna and cable probably need to be replaced every five years, or at least inspected or tested for water intrusion and damage which will cause signal loss. And when you run the new cable, you pay more for premium low-loss cable, fully tinned to prevent moisture damage, or at least, tinned center conductor, with a water resistant solid dielectric. Properly installing the end fittings and sealing the connections with proper waterproofing (not juse some tape) pays you back many times.

And then once the cable and antenna are up to spec, you may still have a problem in your radio. You can buy a meter to test output power, or take it to a shop, or if the radio is old, ask the manufacturer about sending it in for testing and tuning if needed. Yes, sometimes they simply don't age well.

But oddball kludges, combining cables, putting magnets on the microphone cable...(G)...really no need for that stuff. This is a case of just "do it right" and it will work right, and there's no way to cut corners and economize on that.
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Old 19-03-2013, 20:17   #15
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Re: can you combine 2 coax cables?

Do you have to have the antenna on the top of the mast? My boat was hit by lightening a few years ago fusing the VHF coax to the top of the mast. Instead of trying to fix that mess, I installed a 4 foot 1/2 wave Shakespeare antenna off an existing aft pedestal. Theroritically you will lose some range but you will gain db because of the better antenna and shorter coax cable length
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