Second VHF- antenna splitter?? - SailNet Community
 
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post #1 of 9 Old 08-16-2010 Thread Starter
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Second VHF- antenna splitter??

Sorry if this is elsewhere in the forum, I couldn't find it.

I have a serviceable iCom VHF at the nav station of our 50' sloop but want a radio at the cockpit. I have selected what seems like an adequate unit with DSC etc, and will install it soon. I would like to share the use of the same antenna with both the old unit and new unit.

A Google search of "VHF antenna splitter" yields results that range from a $0.65 coax splitter to $250 unit that seems to be powered separately. What do I actually need?

Thanks

Dennis

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post #2 of 9 Old 08-16-2010
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Does your icom have a ram mic capability? May be easier & cheaper than a whole new radio + wiring + splitting.

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post #3 of 9 Old 08-16-2010
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I'd point out if you're going to be installing a second VHF unit, you'd be better off installing a second antenna to give you real redundancy. However a RAM mic makes a lot more sense, if your iCom unit can handle one.

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post #4 of 9 Old 08-16-2010 Thread Starter
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Quote:
Originally Posted by night0wl View Post
Does your icom have a ram mic capability? May be easier & cheaper than a whole new radio + wiring + splitting.
No, I've looked for a RAM mic, and it doesn't seem to; the existing radio is not a top line item. The wiring is not hard; the cockpit location is just 10 feet of service space from the current nav station installation.

Good point about "real redundancy"

d

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post #5 of 9 Old 08-16-2010
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Splitters serve a purpose arguably but all of them share one common problem - loss. The loss of adding the splitter plus the requisite connections with their inherent additional loss usually offsets any benefit to be derived from sharing an antenna. When one considers they can often fail (and you don't know when), the argument(s) against splitters become overwhelming against them.

The obvious question is how much loss - this can't be precisely answered without knowing what splitter and more insidiously, how well or poorly your connectors are made and installed.

Long story short - splitters are a poor choice
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post #6 of 9 Old 08-16-2010
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The obvious question is how much loss - this can't be precisely answered without knowing what splitter and more insidiously, how well or poorly your connectors are made and installed.
However we do know, conclusively, that it will be at least 3 dB (that's 50%) on receive on each radio unless the splitter is "active," because you can't divide something in two without... well, dividing it in two. As for an active splitter: If such a thing existed: You just added another point-of-failure to your radio.

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Long story short - splitters are a poor choice
Concur. Bad idea.

You want VHF in two places: Either add a 2nd antenna or upgrade the existing radio to one with RAM capability and install a RAM. (The latter is what I'd do. If I wanted a backup radio I'd either have a backup radio stashed aboard or a hand-held.)

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post #7 of 9 Old 08-16-2010
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Worst case scenario, you hit a container and grab the mic to call mayday. And, your crew down below grabs the mic down below to do the same thing. What's going to happen with one shared antenna? Nothing good.

Another vote for using a second antenna, or keeping a high quality h/t at the helm. Which is handy if you're using it to call a launch or going ashore and the main power is alreaedy shut down.
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post #8 of 9 Old 08-16-2010
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With a second VHF in the cockpit, you definitely want a separate antenna. I'd put one on the pushpit. It will have plenty of range for the type of transmissions you'd normally do from the cockpit (contacting other boats within visible range, port facilities, etc.).

I have a RAM mic and, while I like it OK I'm not sure I'd go for one a second time. Good waterproof VHF radios can be had for the same price and, with a second antenna, provide 100% redundancy....a good thing.

Whatever you do, don't go the splitter route...losses, potential damage to radios, unnecessary complication, etc., etc.

IMHO,

Bill
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post #9 of 9 Old 08-18-2010
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Quote:
Originally Posted by dtempleton View Post
A Google search of "VHF antenna splitter" yields results that range from a $0.65 coax splitter to $250 unit that seems to be powered separately. What do I actually need?
As an electronics engineer and radio ham, I can tell you that practically speaking, you can split a receive antenna (with the loss others mentioned), but NOT a Transmitter antenna. The $250 unit might be some automatic power-sensing device that is a possible failure point, but otherwise transmitting is going to burn up a passive splitter and possibly the other radio that is still in receive mode (regardless of what channel it is on), and the transmitter won't like it either.

Separate antennas, or a remote control microphone, are definitely the way to go. Two antennas gives complete redundancy, which is hard to beat.

Norman
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