At 22:46 27/04/99 +0200, you wrote:
Hello LowFers,
Added a gallery of pictures to my homepages:
http://www.qsl.net/df3lp
(Antenna, shack, etc.)
Hope it works and will be of interest...
54°16'N / 10°04'E, JO54ag
73 es gl de Peter, DF3LP
Hi Peter & LF-gang,
I just had a look on Peter's homepage (very nice !) and especially to the
pictures of his 'birch-three' LF-antenna.
First of all I have to confirm that the antenna works fine as Peter has a
very good signal with me, compared to the power he runs.
The antenna can be briefly described as a T-antenna, 17m high in the middle
with 2 x 30m topload ending at 13/11m hight. The loading coil is at 12m hight.
Having a closer look at the antenna I noticed that is special is some ways :
1. The vertical section just runs within a tree.
2. The feeding-point is at 12m (just below the loading coil), the antenna
is fed by coax with the inner conductor of the coax connected to the
loading coil and the shield of the coax connected to a metal pipe that goes
the 12m down toward the earth and is grounded there.
So the lower 12m of the vertical part is just a connection to the ground.
This might explain why the antenna is working so well and is not suffering
from too much loss in the three it is mounted in.
In some way it also confirms the 'theory' that the goal of a good
LF-antenna is to bring as much 'power' as possible as high as possible.
According to this theory the ony function of the vertical part of the
antenna is to 'transport' the power to the top (and any radiation by the
vertical part could be considered as waste).
An alternative way to look at it is to make a difference between the
creation of the electric and the magnetic field :
The electric field is created by voltage where the magnetic field is
created by current.
So the top-section of the antenna (all above the loading coil) has a high
voltage and there is a current flowing through it, so this section will
create an electric and a magnetic field.
But the 12m vertical section going from the loading coil down to the ground
is at zero voltage but it is possible that some current goes through it.
The value of this current depends on 'grounding conditions' and wether a
'balun' is used between TX and antenna. But in any case this downgoing
current will only create a magnetic field (that suffers much less from
losses in the earth, threes etc... compared to the electric field).
Anyway, a very interesting antenna.
73, Rik
Rik Strobbe ON7YD
[email protected]
Villadreef 14 B-3128 Baal BELGIUM (JO20IX)
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