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Thread: Mounting a HF antenna

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    Mounting a HF antenna

    I've seen several images of large HF whips mounted on cars. Some are at roof level, some are mounted on the tow bar and others are mounted 1/2 way between. Am I correct in thinking that a roof mount is the most efficient performance wise?
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    Re: Mounting a HF antenna

    I believe the main issue is getting a good earth connection to the car body at the base of the antenna. This is why a single mag-mount does not work on the lower HF bands as it doesn't provide enough capacitive coupling into the roof to provide a low impedance earth at the feed point.

    Coincidentally I've been experimenting with providing additional earthing for a mag-mount on HF by adding earthing straps to a couple of conveniently located bolts that attach the boot lid to the body of my estate. Initial tests are encouraging. Running 10W on 10Mhz I measured 250mA in each earth strap, and it also greatly reduced the current in the wire that earths the ratio case to the car body.
    Best 73 tu
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    Re: Mounting a HF antenna

    That sounds interesting Peter.

    I'm going to be putting a full length roof rack on the landrover soon and was thinking about having a bracket welded on. The rack attaches to the car via 8 large bolts and I may put some aluminum tread plate on the floor of the roof rack.

    How are you measuring the current flow across your earth straps?
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    Re: Mounting a HF antenna

    I use one of these to measure RF current http://g4hup.com/RFC/RFC.htm
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    Peter G0DZB

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    Re: Mounting a HF antenna

    Go to the K0BG website for anything you need to know about HF mobile. K0BG.com

    John
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    Re: Mounting a HF antenna

    What antennas are you planning on using and also what model land Rover.
    If it is a 90/110 then the top of the front wing would be my choice.
    On my Volvo 940 estate, I have a 3/8 mount that bolts through a vertical pannel. Drill 2 holes, one is slightly bigger and has an insulating washer and the coax connects to that.
    And then there is this
    À la perchoine

    Jes

    G-QRP 10080 - RSGB - ARRL

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    Re: Mounting a HF antenna

    Ha ha.... Folding up loop is great until someone forgets that they put a canoe on the roof rack :-)
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    Peter G0DZB

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    Re: Mounting a HF antenna

    Quote Originally Posted by mu0chn View Post
    What antennas are you planning on using and also what model land Rover.
    If it is a 90/110 then the top of the front wing would be my choice.
    On my Volvo 940 estate, I have a 3/8 mount that bolts through a vertical pannel. Drill 2 holes, one is slightly bigger and has an insulating washer and the coax connects to that.
    And then there is this
    It's a homebrew bug catcher style antenna (9' long with the short whip or 13' long with the long whip so only for static use!) and a Freelander. I'm picking up a full length roof rack in a few days so I can mount it on that if higher is better.
    Matt - M0LMK


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    Re: Mounting a HF antenna

    Matt have you seen this https://youtu.be/3_Z7xEW_d7k
    À la perchoine

    Jes

    G-QRP 10080 - RSGB - ARRL

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    Re: Mounting a HF antenna

    Quote Originally Posted by mu0chn View Post
    Matt have you seen this https://youtu.be/3_Z7xEW_d7k
    I have now and I'm not sure if its it's for real or a joke. RF ground is not the same as electrical ground (which is what he tests in that video), the boot mount that he said is great would be useless with a HF whip with it's 4 tiny set screws holding it on and the roof rack mount was a roof bar mount. Was an interesting watch though so thanks

    Here's a picture of the roof rack I'll be fitting. The only difference is that mine will have a rubber covered aluminium floor covering the entire rack floor. I think I'll also bond it to the car with a few 1" copper straps.

    Click image for larger version. 

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    Matt - M0LMK


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