Hello Wolf,
It seems you have well demonstrated that a loop is not optimal. I should remind
that in my "earth antenna" tests, which are comparable to a even more lossy
loop (although this could be compensated by the larger area due to a bad
conducting earth, hopefully). So, if you already have these large towers it is
most probably that you will transmit a signal that is some 10 dB stronger than
with the loop! I am sure you will have success with this vertical!
If you are using an antenna that was resonated on 137 kHz before, remember that
the needed L can be well estimated by the L for 137 kHz and the frequency
ratio: (137/9)^2 ~ 231. So, if you need 1 mH for 137 kHz you will need about
231 mH for 9 kHz.
Can you climb these towers? Than i would recommend to apply the coil as high as
possible on the top of the tower. Take as many as possible wires and make some
toploads. It is the same procedure than on LF ;-)
With EZNEC you can simulate the antenna (if there are not too many trees or
building near the antenna) and may achieve the radiation resistance if you
choose an ideal ground conductivity and no wire losses. Than, you can play with
the length and angle of the top loaded radials and so on.
For a first test you could try a TV transformer as well! Yiu have the great
advantage that DD7PC is able to watch your signal in the near field. This is
optimal for improving things...
Good luck and much fun!
Stefan/DK7FC
________________________________
Von: [email protected] im Auftrag von Wolf Ostwald
Gesendet: Fr 11.06.2010 14:38
An: [email protected]
Betreff: LF: AW: RE: move from loop to loaded aerial
Hi Jim !
Thanks for the info. I already have the antenna structure. I either use a
toploaded vertical abt 25 m high, or I load a long wire same height but much
larger. My question is whether the performance will be the same or not.
I guess as there is no such thing as a free lunch in physics, the vertical will
be the superior performer. Then I have to calculate the antenna`s capacity to
get the inductivity rite.
73 de wolf
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