Just going from memory here, but I think if the vertical height of the outer
end of the active part (ie above the insulator) of the droopy radials is no
lower than around 70% of the vertical height of the upwire, then very little
efficiency is lost. If anyone has a copy of 'VLF Engineering' handy you
could check the actual figure in the chapter on transmitting antennas. The
number of droopy radials may figure in this as well.
73
Dave
ZL3FJ
----- Original Message -----
From: "Ashlock,William" <[email protected]>
To: <[email protected]>
Sent: Tuesday, October 22, 2002 3:21 AM
Subject: LF: RE: Re: Re: Ant Questions
Hi Geri,
>>Do not be tempted to droop the ends of any top wires.
>... I challenge that. My umbrella antenna 18m high with 5 pieces of
top-load
>radials sloping downwards (each about 7 m long) **works fine**
It "works fine" to be sure, and it's possible that this is the only
physical
shape possible for your surroundings, BUT did you verify that there is no
loss from drooping the top hat radials Vs not drooping the top hat
radials?
My experience with many shapes of top hats is that it DOES reduce the
radiation measured in the far field. The theoretical explanation I have
seen
is that the effective height is reduced due to the current foldback.
Bill A
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