At 08:01 PM 19/02/2002 -0500, you wrote:
ZL3IX said:
>> As I am sure you are aware, it's not only the close-in ground system
>> that affects the effectiveness of the vertical, but the conditions in
>> the Fresnel zone as well. Most amateurs are not in a position to do
>> anything about the latter, as it is outside the boundaries of their
>> property. The soil conductivity in WA is not terribly high, so the
>> ground reflection will be very different from that found in an area
>> such as yours.
>
W8JI replied:
>ZL3REX works out much better on an inverted L than on a low
>horizontal. He lives in a valley without particularly good soil
>between high mountains, and has 30 radials on a 70 foot high
>Inverted L. Not a particularly large system, but it is in the clear from
>other antennas, masts and towers.
>
>VK3ZL (also in a poor soil area) works out about evenly comparing
>a dipole at 100 feet or more and a 40 foot radiator with partial coil
>loading and a whip at top, and the rest of the loading at the bottom,
>when conditions are good. He has about 20 or 30 radials. When
>conditions are poor, the vertical is generally better.
>
VK6VZ replied:
Rex ZL3REX is considerably farther from the geomagnetic equator than VK6 -
at a higher latitude where the power coupling into the ionisphere very
definitely favours a vertically polarised antenna.
Bob VK3ZL is at a similar latitude to myself (although at slightly higher
one), where the power coupling JUST favours a vertical antenna. However,
the soil conductivity in Victoria is generally MUCH better than in Western
Australia, so his far field losses are likely to be several dB less than mine.
One of my neighbours/friends in Gle Forrest is an RF consultant who travels
all over Australia, Pacific and the Far East, designing/setting up
point-to-point MF and HF communications systems. He pointed out to me that
in his experience the soil conductivity in the state where Bob VK3ZL lives
is so much better than WA that the ambient noise level is MUCH higher -
because of the fact that the (mainly vertically polarised) noise propagates
so much better. My reply was that I would rather live with more noise for
better propagation of my vertically polarised Tx signals...
The results that Tom W8JI sees from the antenna systems of ZL3REX and VK3ZL
is what you would expect, given their magnetic latitude and ground
conductivity.
Tests with Tom using my inverted vee dipole and Marconi-T generally result
in the inverted vee either being better or (at worst) equal with the
vertical. Unfortunately I don't think the vertically polarised Marconi-T
has ever been better than the inverted vee. Once again, given my latitude
and ground conductivity, this is what you would expect.
In the hour after sunset here, into NA, the inverted vee is generally one
'S' point (or more) better than the Marconi-T. In the hours before
sunrise, the inverted vee is generally two 'S' points (or more) better than
the Marconi-T.
That being said, the Marconi-T is a useful antenna and has provided a new
country in 3D2CI this season - who was unworkable on the inverted vee
dipole. Signals from VK3 - some several thousands of kilometres away - are
often better on the Marconi-T than the inverted vee dipole by several 'S'
units.
Vy 73,
Steve, VK6VZ
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