[UK-CONTEST] Vertical Dipoles

[Clive GM3POI]

Ok 2nd try:
Jim,
     It will make little difference which you choose but I would 
probably go with half wave verticals. This is so your loss appears at 
1/4 wave away from the antenna i.e  At sea. It also gives you a little 
more gain
      Using a 1/4 wave antenna may mean more loss, the maximum current 
being at the base feed point.
    BTW. The vertical dipole can be bent in the vertical plane with up 
to a 90 degree included angle between each element half. This also 
brings down the feed Z.  Needs Modelling ideally but try it.
      Raising the feed points of your 1/4 or 1/2 wave vertical higher, 
can be a bad move (i.e 6m or more) as it will split the vertical lobe 
and you may end up with more gain at a too higher wave angle. This 
really needs to be modelled against the known terrain.
     We have recently completely changed an idea of using 4Sq s near the 
sea for this reason.  With Just a 6m elevation we would have ended up 
with maximum gain at something in excess of 25 degrees, No good for 
anything.
     In your case the next step would be to add gain to the antenna, but 
this adds complexity.

      But your right anyone using Horizontal antennas near the sea is 
wasting  RF in terms of getting any advantage in gain or low angles.

73 Clive GM3POI



On 25/07/2011 13:49, mm0bqi wrote:
Following some very helpful and interesting comments last year about my 
IOTA
contest ground plane antennas I have gone for a change this year.   During
our recent EU108 expedition we tried vertical dipoles beside the sea and
they seemed to work.  However I am not fully convinced but feel it is worth
having a go!  I have two questions.
1.  Will there be any great performance difference between the two types of
antenna?  My main target area is EU and I have a clear sea path to VK/JA
should the bands open....
2.  The antennas will be on 12m fishing poles, does the height of the feed
point matter or should I just make it as high as possible?
Each antenna 10/15/20m will be taped to a separate 12m fishing pole and
they will be within 5m of the sea.  The coax will come away at right angles
along a cane for about six feet then slope to the ground at about 45
degrees.
Thanks
Jim,  MM0BQI
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