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  1. #11
    Join Date
    Jul 2003
    Location
    West Australia
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    11,515

    Default Re: Radio wave experts - Radar reflector on whip aerial

    That type of VHF antenna is designed to work with no external ground plane so definitely not a simple dipole. The components usually a coil and tuning capacitor and various radiating elements are housed in the grp tube. So much would depend on the location or the radar reflector in relation to the internal components. So IMHO almost certainly going to detune the antenna resulting in much less RF power going out. Now of course you may never notice the difference but it might just make a difference one day at extreme range so I would not mount the radar reflector on the antenna. ol'will (plus I think people who see it will think you a fool)

  2. #12
    Join Date
    Apr 2005
    Location
    Exmouth, Devon
    Posts
    660

    Default Re: Radio wave experts - Radar reflector on whip aerial

    I think I'd be just as concerned about the strain on the antenna. Simply not designed to carry something like that. Your bigger risk is breaking the antenna.

    The small tube reflectors are only any good for scrutineering purposes. Unless you are entering a race where they are required and you want bare minimum, then no point. IIRC the rules say 'where practicable' but if you're going to the trouble for your own safety you might as well use a real one. Doubt any private vessel has ever been prosecuted for lack of reflector.

    You can get that type with a deck mount which you could put on the other side of coach roof. If you can get the 4" one in that style, even better. You can also get the Echomax as a deck mount.

    Johnalison suggested they should be horizontal but vertical is the correct orientation.
    allGadgets Marine
    www.allgadgets.co.uk

  3. #13
    Join Date
    May 2007
    Posts
    36,168

    Default Re: Radio wave experts - Radar reflector on whip aerial

    Quote Originally Posted by William_H View Post
    That type of VHF antenna is designed to work with no external ground plane so definitely not a simple dipole. .....)
    Dipoles don't generally have ground planes anywhere near them.

  4. #14
    Join Date
    Feb 2007
    Location
    Essex
    Posts
    21,749

    Default Re: Radio wave experts - Radar reflector on whip aerial

    Quote Originally Posted by MikeCC View Post
    I think I'd be just as concerned about the strain on the antenna. Simply not designed to carry something like that. Your bigger risk is breaking the antenna.

    The small tube reflectors are only any good for scrutineering purposes. Unless you are entering a race where they are required and you want bare minimum, then no point. IIRC the rules say 'where practicable' but if you're going to the trouble for your own safety you might as well use a real one. Doubt any private vessel has ever been prosecuted for lack of reflector.

    You can get that type with a deck mount which you could put on the other side of coach roof. If you can get the 4" one in that style, even better. You can also get the Echomax as a deck mount.

    Johnalison suggested they should be horizontal but vertical is the correct orientation.
    The ones I have seen have the elements disposed in line with the tube and will have no reflecting apices when vertical as with the octagonal type. I'll have another look when I see one in case here are other designs.
    Far away is near at hand in images of elsewhere

  5. #15
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,171

    Default Re: Radio wave experts - Radar reflector on whip aerial

    Quote Originally Posted by superheat6k View Post
    Indeed I appreciate the effect is likely marginal , but it is the sole legal requirement for a boat of my size under SOLAS regulations. I am now compliant, although I appreciate a vast majority are not.

    However, is my effort to achieve legal compliance (that most don't bother with BTW) compromising the real value of the VHF radio as a key safety device (NB a VHF Radio is NOT required by SOLAS as I understand it) ?
    All vessels must also have available an illustrated table of the life saving signals given by ships aircraft and persons in distress. http://solasv.mcga.gov.uk/mca%20docs...ing%20sigs.pdf
    MCA advice is that this should be prominently displayed in the wheelhouse.
    Last edited by VicS; 16-05-19 at 09:36.

  6. #16
    Join Date
    May 2007
    Posts
    36,168

    Default Re: Radio wave experts - Radar reflector on whip aerial

    Quote Originally Posted by VicS View Post
    All vessels must also have available an illustrated table of the life saving signals given by ships aircraft and persons in distress. http://solasv.mcga.gov.uk/mca%20docs...ing%20sigs.pdf
    MCA advice is that this should be prominently displayed in the wheel house.
    The Wheel House, that's a pub in Plymouth I think?

  7. #17
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,171

    Default Re: Radio wave experts - Radar reflector on whip aerial

    Quote Originally Posted by lw395 View Post
    The Wheel House, that's a pub in Plymouth I think?
    Capitalised maybe but actually in both cases it should be one word, now corrected in my post.

  8. #18
    Join Date
    Jan 2012
    Location
    South Coast
    Posts
    5,040

    Default Re: Radio wave experts - Radar reflector on whip aerial

    Quote Originally Posted by William_H View Post
    ... (plus I think people who see it will think you a fool)
    For the last comment, I reckon many already do, but fortunately I do not give a sh1t.
    Interested in Corvettes PM me for details of the Corvette Motorboat Association

  9. #19
    Join Date
    Jul 2003
    Location
    West Australia
    Posts
    11,515

    Default Re: Radio wave experts - Radar reflector on whip aerial

    Quote Originally Posted by lw395 View Post
    Dipoles don't generally have ground planes anywhere near them.
    Yes you are right. My senior's moment again. 1/4 wave antenna should be substituted for dipole. However in fact the tube may contain a dipole with the lower 1/4 wave length piece in lieu of ground plane connection or as a ground plane.
    So to be honest I don't know what is inside the tube. ol'will

  10. #20
    Join Date
    Dec 2006
    Location
    on the boat
    Posts
    1,238

    Default Re: Radio wave experts - Radar reflector on whip aerial

    That type of antenna is usually a 5/8 wavelength whip. These are either stub tuned or coil tuned at the base. It is not advisable to hang any metal from them as it will affect the tuning. This can have the effect of a greater SWR causing power to be reflected back into the transmitter, if its too high it could lead to damage of the final transmit stages of the VHF.
    Would I do it ? No is the answer as it will affect transmit / receive to a greater or lesser extent and it may just make the difference between being heard or not in the case of an emergency.

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