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    Re: Lights etc. - aluminum foil in mast
    From: Brooke Clarke
    Date: 2003 Oct 11, 20:59 -0700
    Hi Gerard:

    I don't understand your question about the "array (rain catching side up) honeycomb?"
    What you are referring to is called a corner reflector.  The idea is that a signal will bounce off three surfaces so the bean ends up going back in the same direction where is came from.  You mentioned some good examples of the car tail light, or passive reflectors.  But for this to work the three surfaces need to be at right angles to each other and be larger than some part of a wavelength (maybe a whole wavelength, not sure).

    The buoy with an aluminum sheet on the top sounds a lot like the surfaces on a stealth fighter.  The idea is that a reflecting surface will bounce the radar off to somewhere other than back to the sender.  What would have worked would be just a wire cut to a half wavelength.  Better would be three such wires at right angles to each other.

    Have Fun,

    Brooke Clarke, N6GCE





    Gerard Mittelstaedt wrote:
    Hi,
     Yes, the Aluminum Foil crunched up in the mast was
    recommended for those making hollow wooden masts, that,
    it was recognized, would not give much of a radar reflection,
    if any at all.
    
    Some 30 years ago I bought a "Firdel Blipper" radar reflector
    (looks like a 12 inch diameter cylinder with rounded ends,
    about 2 feet long).  When raised up in the rigging, and when
    I was proceeding down the Intercoastal Waterway in Texas, USA
    The barge tows I met never looked like they were surprised...
    even "around corners" of the channel they knew I was there
    before they could see me.  This was long before I had VHF radio,
    and I did have a wooden mast, though a solid one.  (Very old boat
    -
    Tahiti ketch, built in 1941.)
    
     The Firdel Blipper is supposed to have a
    rigid array of thin aluminum plates at right angles to one
    another so that they give the best reflected return... like a
    lens on an automotive tail-light, or those plastic reflectors
    on automobiles.  Is the array (rain catching side up) honeycomb?
    
    When I worked for a geophysical company offshore in the Gulf
    of Mexico we sometimes put our bouys to re-calibrate radio
    navigation...(LORAC) (This was in 1971. No GPS... and LORAN
    was not accurate enough for our purpose.)
    The bouys were cubic chunks of foam, with an 8 ft (just under
    3 meter) bamboo pole through the foam weighted on one end... and
    a plastic flag on the top.  I tried adding some aluminum foil
    to the top, rather like a flag, to help finding the bouy in the
    morning with the radar... It turned out that this was no help
    at all, as a single sheet of aluminum seemed to be invisable...
    was the frequency wrong, or did the sheet shape scatter the
    radar signal off so that it did not return?
    
    Anyway - lesson learned was that just a bit of metal in the
    air did not make a good radar reflector.
    
    Gerard Mittelstaedt    mitt{at}hiline.net
    McAllen, Texas
    USA
    
    Peter Fogg wrote:
      
    ----- Original Message -----
    From: "Jared Sherman"
    
        
    <stuff the mast with balled-up aluminium 'paper> simply cannot work. The
          
    usual heavy aluminum mast is radar opaque, nothing inside it could make a
    difference.
        
    That makes sense. I wonder if what I'm remembering was a home-made radar
    reflector from the days of wooden masts.
    
        
     Unless someone has gotten a local exemption from the laws of physics ...
          
    This is a good idea, worth exploring further ...
        
    
    --
    ---------------
    Gerard Mittelstaedt    mitt{at}hiline.net
    McAllen, Texas
    USA
    
    
      
       
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