Hi Jim,
Thanks for your insight on the topic.
The proof is in the pudding I guess.
I will not know the answer until its actually try it.
Right now I need to get my coil wound get on the frequency and experiment
from there.
Thank you again Jim
BTW I ezenec+ so I will try to model it.
PauLC
-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of James Moritz
Sent: Tuesday, April 06, 2010 3:39 PM
To: [email protected]
Subject: LF: Re: 9 Khz Antenna update Putting inductance near the top.
Dear Paul, Rik, LF Group,
Well, I hate to be a pessimist, but I am not convinced that elevating the
loading coil will be particularly useful at W1VLF.
There seem to be 2 ways an elevated loading coil could be of benefit. One is
that it effectively reduces the impedance of the top-load section of the
antenna, so increasing the proportion of the total antenna current flowing
in the top load "above" the coil. This improves the current distribution and
so increases the effective height. This could be very useful where the top
load part of the antenna is fairly small compared to the vertical part. But
in Paul's case, the top loading wires will already carry quite a large
proportion of the total antenna current. Also, most of the top loading wires
will be below the height of the coil, so diverting more current into them
will not be particularly beneficial from this point of view.
The other possible benefit would be where the antenna downlead runs close to
a mast, building, tree etc. The elevated coil will reduce the voltage on the
downlead, reducing the displacement current flowing in the nearby objects,
and so reducing losses associated with this unwanted capacitance. But from
Paul's description, it does not seem that the downlead will be particularly
near anything.
I would reccomend feeding the antenna geometry and likely loading coil
inductance into some NEC-based antenna simulator software to see if it is
actually beneficial to the effective height/Rrad of the antenna. But I would
be surprised if the elevated coil made a significant improvement, and it
would be a big lump dangling from the top of the mast there...
Cheers, Jim Moritz
73 de M0BMU
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