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Thread: High Gain VHF Whips

  1. #16

    Re: High Gain VHF Whips

    You could also try an 8 ft 6db Glomex antenna, available from TMQ. These have the cable running into the antenna. They’re quite a heavy antenna though, so I use a stainless knock down mount. I have one of these on my hard top and used to find it very good when offshore from Townsville.

  2. #17

    Re: High Gain VHF Whips

    ^another vote for Glomex. Got a Glomex as my phone aerial. My phone service is better than VHF up at Noosa Canyons for getting a text out V hitting the 21/22/80 repeaters. My 8" Pacific goes good as my VHF aerial. In our gamefish club there are three freak radios. My iCom M412 matched to an 8" Pacific, a Kevlacat with one of of the old push button face GMEs and surprisingly a 575 Cruise Craft with a stock standard GME and GME aerial. Ship to ship we are all hitting each other about 15nm apart, more than the line of sight of say 10nm you would expect. We are outperforming the flybridge game boats with better line of sight for some reason. When I am running in I often hear one sided conversations from these boats when they are east of the Barwons and I am nearly at the Mooloolaba rock walls. I can't explain it but that is what happens in real life.

  3. #18

    Re: High Gain VHF Whips

    Know what you mean Smithy, as the original GME aerial wouldn't raise Mlba CG once I got close to Murphy's, I replaced it with the Navman (pacific)aerial and I called into them several times from the bottom end of the Barwons and had excellent transmission and reception with them, the constant chatter from other boats was annoying at times as I'd be getting conversations from boats out at Tempest, Bribie CG etc, I had to turn the gain down. Due to an oversight of mind I left it up very early one morning and cracked it on a tree, it still worked but range dropped dramatically over time. So sounds like my combination was also a freak setup, was hoping I'd get back to something like that again.

  4. #19

    Re: High Gain VHF Whips

    Quote Originally Posted by scottar View Post
    The gain is a comparison to a Isotropic Radiator (theoretical radiation pattern that has equal signal in all directions) that is created by the way the antenna compresses the radiation pattern. Things like half wave, quarter wave etc refer to the antennas length/construction which basically sets how they create their respective gains.

    https://www.air-stream.org/technical...ted-power-eirp

    If you think of the radiation pattern as a donut of a certain volume - the more you squash the donut, the further it will move out from the centre. This is essentially the effect of increasing an antennas gain - more out with less up and down.
    Still trying to get my head around this. Does this mean that a 3db half wave antenna is theoretically equal to a 6db single wave for gain horizontally but half height in the vertical range. If this is the case does that also mean in rough seas comms could be sporadic as the horizontal portion of the wave could be bouncing up and down, a bit like a spinning coin that is on its last legs wobbling all over the place.

  5. #20

    Re: High Gain VHF Whips

    Quote Originally Posted by Dignity View Post
    Still trying to get my head around this. Does this mean that a 3db half wave antenna is theoretically equal to a 6db single wave for gain horizontally but half height in the vertical range. If this is the case does that also mean in rough seas comms could be sporadic as the horizontal portion of the wave could be bouncing up and down, a bit like a spinning coin that is on its last legs wobbling all over the place.
    No and yes Sam. See the attached pic - "Aerial basics by a dummy who can't draw real good either"

    Radiation Patterns.jpg

    Consider diagram "A" as a standard unity gain whip antenna radiation pattern side on view. As the gain of the antenna increases - pictures B & C - the distance the signal travels in a horizontal direction becomes bigger but the angle of spread becomes less. Pictures D and E give a rough idea of what can happen in rough seas (and also why the "go fast look" isn't a great idea for radio performance) if an antennas radiation pattern is too compressed (goes hand in hand with very high gains). These are extremely simplistic representations as there are other things going on typically as well - sidelobes, interference to the radiation pattern from surroundings etc.

    Don't get too hung up on a manufacturers description of the antenna - the main things you are interested in from an end users perspective is the gain and the construction being capable of withstanding the marine environment.

  6. #21

    Re: High Gain VHF Whips

    That's pretty good Scott, thanks for going to the effort, makes more sense now. Looking for a place on the Sunny Coast that will have decent aerials available, Brendale is still a bit far for me at this stage, this sitting around waiting to heal is an absolute PIA.

  7. #22

    Re: High Gain VHF Whips

    Quote Originally Posted by Dignity View Post
    That's pretty good Scott, thanks for going to the effort, makes more sense now. Looking for a place on the Sunny Coast that will have decent aerials available, Brendale is still a bit far for me at this stage, this sitting around waiting to heal is an absolute PIA.
    😂😂😂.....effort?? If I could find a kid around here that hadn't eaten their crayons you would have got the pics in colour. Try Linemaster in Maroochydore mate. Sugar road. Google will find him.

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