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Old 05-07-2013, 10:00   #1
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VHF range and static trouble

My VHF communications have always made me feel like I'm not reaching very far. I also seem to get a lot of static even while talking to someone close by.

I just added an AIS transceiver to the boat. It is confirmed, a following AIS boat didn't come on the screen until about 1 mile away. I called him on VHF and he said that I just showed up on his screen too and that I was intermittently coming on and off.

I have the standard short flexible VHF antenna at the top of the mast. I think I need an expert in Boston/Plymouth are to check it out but even if I do:

Is it advisable to upgrade to the ~5' stiff longer range antenna's? (Height is not an issue since we are 76' already we won't be ICW worthly anyway) We are going to be world cruising and I'd like to see cargo ships from far away!

Anybody know a tech in the Boston/Plymouth area that is an expert on the subject?

Mark Powell
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Old 05-07-2013, 10:26   #2
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Re: VHF range and static trouble

Hi Mark,

There is a little meter called an VSWR meter. Does your AIS come with PC softwear?
Is it a raymarine or AIS that uses Pro-AIS2? Because there is a VSWR meter built into that program.

You plug your AIS into the Laptop and connect and the diagnostic page and you will see the VSWR Ratio. if the ratio is 1:1 you are sensational! If its 1:999 you are not transmitting far at all.
My mast head antenna is 1:1.1 and thats almost unbelievably good.
My aft antenna is 1:1.5 which is excellent.

If your is over 1:2 then you antenna is stuffed or your cable is stuffed, or your connectors are stuffed.

Mark
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Old 05-07-2013, 12:18   #3
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Re: VHF range and static trouble

The short antenna should work fine if there are no problems with the connectors, cables, or antenna. On a sailboat the shorter antenna is probably best, because when you heel the longer antenna's high-gain radiation pattern might be pointing towards the sky or the water. A shorter antenna is more forgiving in this regard.

Anyway, the problem is not that the antenna is short. As Mark says above, try to test the SWR. If your AIS setup doesn't have a built-in SWR measurement capability, buy or borrow an SWR meter and test the antenna / cable using your VHF radio.
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Old 05-07-2013, 12:28   #4
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Re: VHF range and static trouble

Thanks guys!

It is a Raymarine and I have the software. I'll check that out!

Mark
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Old 05-07-2013, 14:37   #5
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Re: VHF range and static trouble

The advice on the 3' whip antenna is good. Having a longer antenna with more gain won't gain you much, if anything.

The advice on connector problems is right on the money. Over the last 15 years of marine electronics work, almost 80% of the PL-259 connectors are poorly assembled.

Check the cable type. If you have the small RG-58 wire, even under perfect conditions you will lose about 75% of the power over a 100' run.

Finally, measuring the VSWR is often NOT a good indication of whether the antenna is working. The SWR measurement only works properly when performed at the base of the antenna, not very practical when the antenna is 75' up. Losses in the cable (see previous item) will make the SWR measured at the radio look good even if the antenna isn't working at all.
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Old 05-07-2013, 14:46   #6
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Re: VHF range and static trouble

Jim installed a new vhf cable when we had the mast out earlier this year. Our AIS now picks up the big guys at 100 miles, instead of 25. So I'm agreeing with all the other guys, connections, proper installation of the plugs, good quality cable, and keep the water out!

Ann
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Old 05-07-2013, 15:07   #7
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Re: VHF range and static trouble

I had the same trouble - unbelievable static. Even at maximum squelch the static broke through. My AIS is on a separate antenna so that wasn't an issue.
I recently had the mast out and decided to replace the antenna and the wire going up - the difference is unbelievable !!! The radio is now usable again.
I left the old antenna cable in the mast but removed the connector at the top and a few inches of the wire - the cable seemed good but it was corroded. All corrosion was removed with the short section of cable that was cut. The new connector was crimped, heat shrunk with double layer heat shrink and wrapped in self amalgamating tape and stuffed into the top of the mast in case I need it or if I want to install a different antenna (possible 2 meter ham antenna).
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Old 06-07-2013, 01:41   #8
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Re: VHF range and static trouble

I'm having the same problem. I had the antenna replaced four weeks ago, after that my Standard Horizon GX2100 worked great, crystal clear coverage. Then two weeks ago, I had a PA horn added on the mast along with a small Garmin GPS added for AIS coverage. Now all I get is static along with the voice transmissions received. Even with the squelch turned way up. When I first power up the unit, no static for the first few minutes, then it gets progressively worse. Any ideas? The second guy who worked on adding the AIS looked like he knew what he was doing, but things haven't worked right since. The AIS seems to be functioning fine, just the static problem.

I can hardly understand distant transmissions. Transmissions from close by within the harbor are clear.
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