[TowerTalk] Tree attenuation

Marlon K. Schafer (509) 982-2181 ooe at odessaoffice.com
Tue Nov 8 10:57:30 EST 2005

Anyone know where we can get our hands on that research?

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----- Original Message ----- 
From: "Jim Lux" <jimlux at earthlink.net>
To: "Frederick M. Mott" <ab8ah at earthlink.net>; "'Jim Brown'" 
<jim at audiosystemsgroup.com>
Cc: <towertalk at contesting.com>
Sent: Monday, November 07, 2005 4:49 PM
Subject: Re: [TowerTalk] Tree attenuation

> At 04:20 PM 11/7/2005, Frederick M. Mott wrote:
>>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 
>>A sister station, AB8AAB, 2nd Bde of the 1st Inf Div was located in a 
>>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.
> It is precisely the sort of thing you observed 40 years ago that prompted
> the research of George Hagn at SRI (and others, like Tamir) on propagation
> through or around forests and jungles.  They went out and did a bunch of
> testing, first in Eucalyptus forests around Palo Alto, CA, then in forests
> in Australia, and finally in actual jungle.  This test campaign also
> prompted the development of the Open Wire Line technique for measuring
> ground dielectric properties because their measurements that used the
> measured feedpoint impedance of  (low) dipoles were suspect.  SRI also
> developed the RELEDOP technique to measure 3D far field patterns of HF and
> VHF antennas.
> There was some research after that, but really, all the work and analysis
> was done back then, and not much has changed since then, there being no
> commercial need anymore.  These days, HF propagation research foucuses 
> more
> on Over The Horizon radars, typically for observation of ocean surfaces,
> and they manage to put their antennas in places without trees or forests.
> (and a bit of work on spectral monitoring in an OTH sense, to look for 
> "bad
> guys" talking on their HF radios)
> Given that lots of tactical radios work in the 30-88 VHF band, and the US
> military emphasis on being able to fight a land war in Europe, there was a
> moderate amount of research on propagation at those frequencies in
> temperate forests, which manifests itself in the papers from the late 70s
> and early 80s.
> There's also a huge amount of work in the 800 MHz area in that time 
> period,
> supporting cellular telephone applications.  Lots of guys driving around 
> in
> monitoring vans making precision field strength and multipath measurments
> The research these days is all on various microwave frequencies (think in
> terms of cellular, PCS, and WLAN applications), and more often than not,
> for urban environments.  There's also a fair amount of research on this
> (particularly about 10 years ago) to support various satellite to mobile
> applications (like Sirius and XM <grin>) which oddly, the customers expect
> to work when they're driving through the forest as well as through the 
> city.
> It's all about money, after all... If you want to do research, you've got
> to do something that will let you eat and pay the rent (there's only a
> limited amount of truly philanthropic money out there) and that means
> having someone with cash interested in the data.  McArthur grant screeners
> may contact me at my email address. I'll be happy to take this on for a 
> few
> years, and half a million dollars would probably be enough to do a decent
> measurement and analysis campaign.
> I suspect that if we were ever to be involved in a significant ground war
> in a forested environment, folks would start paying attention to HF and 
> propagation in forests again.  For now, though, the existing solutions
> (manpack and vehicular HF and VHF radios with ALE) work "well enough". 
> You
> too can own the current state of the art for about $20-25K.
>>-----Original Message-----
>>From: towertalk-bounces at contesting.com
>>[mailto:towertalk-bounces at contesting.com] On Behalf Of Jim Lux
>>Sent: Monday, November 07, 2005 5:13 PM
>>To: Jim Brown
>>Cc: towertalk at contesting.com
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