Anyone know where we can get our hands on that research?
thanks,
Marlon
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----- Original Message -----
From: "Jim Lux" <jimlux@earthlink.net>
To: "Frederick M. Mott" <ab8ah@earthlink.net>; "'Jim Brown'"
<jim@audiosystemsgroup.com>
Cc: <towertalk@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
>>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.
>
> 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
> VHF
> 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@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
>
>
> _______________________________________________
>
> 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.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
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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