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Important Discovery Garmin AIS-gctid385230

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    Important Discovery Garmin AIS-gctid385230

    Have noted my VHF radio performance has degraded since I installed a Garmin AIS system. I did some checking before I installed it last summer and Garmin says the loss is about 0.5 dB. Well our first cruise this year, our VHF hardly worked at all. Remembered that last fall, I did some wiring changes on the AIS at it was not shutting off automatically when I shut down the Garmin plotter. Well this is what I found today. I used a VHF radio meter to measure power and VSWR at the radio. When the antenna is hooked up directly to my VHF antenna, the radio measures a clean 25 watts out and a good 1.1 to 1 VSWR. When I run the antenna through the AIS with the AIS off, my radio test showed only 10 watts out and a VSWR of 3.0 to 1. When I turned on the AIS the radio improved somewhat to a power out of 20 watts and a VSWR of 1.5 to 1. Well I am for sure going to add a separate VHF antenna for the AIS. I am now looking for the shortest smallest VHF antenna I can find, a foot overall length would be excellent. I do not need to see boats over a few miles away, certainly not more than 5 miles to clutter up the plotter when I change scales. Any ideas for a very short VHF antenna?
    Started boating 1965
    Bayliners owned: 26 Victoria, 28 Bounty, 32, 38, and 47 since 1996

    #2
    Most of the dedicated AIS antenna are 4 foot.

    Shakespeare has some 3 foot in their older series of antenna.
    Jim McNeely
    New Hope a 2004 Bayliner 305 Sunbridge Express Cruiser
    Twin 5.7s with Bravo2 drives
    Brighton, Michigan USA
    MMSI # 367393410

    Comment


      #3
      The Shakespeare emergency VHF antenna typically carried by sailboats in case of dismasting is about a foot long. It comes with a suction cup mount but would be easily adaptable.

      Comment


        #4
        You need to have about 18" (1/4 wave) if you have the antenna mounted on a metal counterpoise, such as a metal arch. Otherwise, you need at least an electrical 36" (1/2 wave) to have any kind of coverage without a counterpoise.

        Otherwise, you are just hanging out a piece of wire and you take what you get. Odd lengths other than mentioned may even work better when they aren't vertical, at least in some directions.

        I suggest the 1/2 wave antenna from Metz. Virtually indestructable and low profile from a visual aspect. I have them up in both VHF and UHF as backups and I'm very pleased with the performance. Here's a link to the VHF Marine model: http://www.metzcommunication.com/manta6.htm

        Splitters of any kind can be nasty. You could probably solve some of the problem by adjusting the coax length between the radios and the splitter, but, that's a real pain to get right.

        Comment


          #5
          I added a dedicated antenna to mine as well. Didn't notice any degradation really, but wanted to be sure there was no loss.

          Love the AIS 600 btw.
          Custom CNC Design And Dash Panels

          iBoatNW

          1980 CHB Europa 42 Trawler- "Honey Badger"

          Comment


            #6
            JohnWms wrote:
            The Shakespeare emergency VHF antenna typically carried by sailboats in case of dismasting is about a foot long. It comes with a suction cup mount but would be easily adaptable.
            rodell wrote:
            You need to have about 18" (1/4 wave) if you have the antenna mounted on a metal counterpoise, such as a metal arch. Otherwise, you need at least an electrical 36" (1/2 wave) to have any kind of coverage without a counterpoise.

            Otherwise, you are just hanging out a piece of wire and you take what you get. Odd lengths other than mentioned may even work better when they aren't vertical, at least in some directions.

            I suggest the 1/2 wave antenna from Metz. Virtually indestructable and low profile from a visual aspect. I have them up in both VHF and UHF as backups and I'm very pleased with the performance. Here's a link to the VHF Marine model: http://www.metzcommunication.com/manta6.htm

            Splitters of any kind can be nasty. You could probably solve some of the problem by adjusting the coax length between the radios and the splitter, but, that's a real pain to get right.
            Man, we have some really good technical people on BOC who only drop in once in a while. Seriously, you guys should come out to play more often. :worth

            Comment


              #7
              I put a second 8' antenna up for the AIS. The reason is twofold; AIS Class B transceivers only put out 2W so a short 3db emergency antenna was tempting (visually) but the full 6db gained from the Shakespeare 5225 was worth it. Second reason, if I ever lose the primary VHF antenna, I'll have a spare ready to connect in. Ya never know when a connector is gonna rot away or a coax gets pulled apart. Having two gives me redundancy and a much greater range for both receive and transmit.

              I get signals very consistently out at around 15-17 miles even when under our boat shed.
              Custom CNC Design And Dash Panels

              iBoatNW

              1980 CHB Europa 42 Trawler- "Honey Badger"

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