I operated a MARS station (AB8AH - 1st Bde 1st Inf Div) in Phouc Vinh than
in Quan Loi, Viet Nam during 1967 and 1968. There were no trees at both
locations near our towers (100 ft Rohn 25G and a 70 ft commercial tower)
except for 1 palm tree (about 20 ft and 1 10 ft banana tree). Our site
worked very well, we ran approximately 1,100 to 1,200 phone patches a month.
A sister station, AB8AAB, 2nd Bde of the 1st Inf Div was located in a rubber
plantation (jungle environment)at Lai Khe. Their wire beam was suspended
from the rubber trees. They were lucky to run 50 phone patches a month.
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Jim Lux
Sent: Monday, November 07, 2005 5:13 PM
To: Jim Brown
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] Tree attenuation
At 01:24 PM 11/7/2005, you wrote:
>On Mon, 07 Nov 2005 12:15:59 -0800, Jim Lux wrote:
>
> >As far as HF goes, it gets quite a bit more complicated(!), for two
reasons:
>
> >1) The forest scale (height of trees, etc.) is on the same order as the
> >wavelength (at VHF, trees are MUCH bigger than a wavelength, and leaves
> >are MUCH smaller).
>
> >2) Most practical applications of a model have the antenna in the forest,
> >where the forest is in the near field of the antenna.
>
>I skimmed both the Power Point and the longer document. The analysis that
>went
>into the Power Point make it considerably more valuable in guestimating
what
>might happen at VHF and low UHF, but neither gives much insight into HF.
>
>The obvious question is, is anyone aware of anything equally good for the
HF
>spectrum? My future antenna supports are likely to be redwoods, 25-30
meters
>tall.
The short answer is no.
There's not much research interest in HF frequencies at least as far as
propagation through forests. People who have serious money to spend on HF
antenna installations where loss would be important either site them were
there is no forest or cut down the trees.
There is some propagation data from the 60s and 70s, collected for jungle
type environments. There's also some recent low VHF data from Brazil, also
for a jungle.
There's no nice summary presentation all put together, unfortunately.
It might be worth calling or writing Vogel at U of T Austin.
>Jim Brown K9YC
Jim Lux, W6RMK
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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