The ladder on the outside of the corn crib is probably a little less than 20
feet.  I have seen the beacon close to 25 miles away.  It is a bright amber
rotating beacon. Yes at 31 foot, the LOS should be there, but more than half
of the Fresnel zone will be impeded.

-----Original Message-----
From: wireless-boun...@wispa.org [mailto:wireless-boun...@wispa.org] On
Behalf Of Josh Luthman
Sent: Tuesday, February 23, 2010 9:12 AM
To: WISPA General List
Subject: Re: [WISPA] That black magic

That profile suggests at 31 feet the customer should see the light
(the black LOS line).  Was that where they looked for the light, or
lower?  I would have to guess the corn crib was not nearly 31 feet.

I think the whole US has 3m and 10m data -
http://www.cplus.org/rmw/dataen.html

Josh Luthman
Office: 937-552-2340
Direct: 937-552-2343
1100 Wayne St
Suite 1337
Troy, OH 45373

“Success is not final, failure is not fatal: it is the courage to
continue that counts.”
--- Winston Churchill



On Tue, Feb 23, 2010 at 10:05 AM, Mike <m...@aweiowa.com> wrote:
> I have a bright beacon I can turn on at the top of this tower.  On a clear
> night recently, I turned it on.  Even a ways up a corn crib he could NOT
see
> the light.  I think the terrain data is accurate.  The alphimax site, once
> you create the path lets you go into Google Earth and "see" the hill.
 This
> part of the world doesn't have high resolution imagery archived yet, but I
> CAN see the ridge when I follow along the path.
>
> -----Original Message-----
> From: wireless-boun...@wispa.org [mailto:wireless-boun...@wispa.org] On
> Behalf Of Josh Luthman
> Sent: Tuesday, February 23, 2010 9:01 AM
> To: WISPA General List
> Subject: Re: [WISPA] That black magic
>
> To begin with, are you sure there is a bump there?  Could it be bad
> meter resolution?
>
> Josh Luthman
> Office: 937-552-2340
> Direct: 937-552-2343
> 1100 Wayne St
> Suite 1337
> Troy, OH 45373
>
> “Success is not final, failure is not fatal: it is the courage to
> continue that counts.”
> --- Winston Churchill
>
>
>
> On Tue, Feb 23, 2010 at 9:55 AM, Mike <m...@aweiowa.com> wrote:
>> I need to do a reality check with those of you familiar with knife edge
>> diffraction as a propagation medium.  First, I should paint the scene:
>>
>>
>>
>> I have a corporate farmer almost 16 miles away who is motivated.  His
>> options are satellite, dialup he currently uses, or us.
>>
>>
>>
>> A spectrum sweep of the property found absolutely no 2.4 signals.  By in
>> large, these rural areas are very quiet.
>>
>>
>>
>> There are no trees or obstructions in the near field or out quite a ways.
>> However, there is a ridge almost half way between us.  I am embedding an
>> image of the path here created with alphimax.com path estimator.
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> I have a test unit which is a 19 dB panel/radio with an AP fastened to
the
>> back.  It lets me hand hold a test unit and see what it sees on a laptop.
>> Standing on the ground on his property we got an ALMOST usable signal in
a
>> short test.  He has a 35 foot TV tower next to the house on which we
would
>> install.
>>
>>
>>
>> Perhaps one would look at the path profile and common sense would dictate
> it
>> won't work.  However, I use knife edge diffraction successfully on a
> handful
>> of installs.  Besides, black magic sometimes trumps common sense.
>>
>>
>>
>> I have never used this technique where the ridge is close to mid point.
>  On
>> all others the ridge was closer to the user.  All of them work except
when
>> tropospheric ducting enters into the equation, with one exception.  I
have
>> told the users this is a 98% link and it WILL go down during those
events.
>> Earlier this winter we had a few days of ducting which caused a couple of
>> them to fade.  I saw a 15 dB fade on those.  Statistically, ducting
should
>> only affect this area 20 some hours a year.
>>
>>
>>
>> The single exception was when the obstructing hill had soy beans growing
> on
>> it.  That particular one went down in late fall when the beans were ready
>> for harvest.  The previous 2 years the field had corn planted on it and
> had
>> absolutely no issues.  I think dry beans affect the signal because they
> are
>> no longer "row" polarized and randomly scramble the signal beyond use.
>  Once
>> the beans were harvested, the signal came back like usual.
>>
>>
>>
>> On this path in question, I found the ridge.  There are no trees, instead
> it
>> is farmed.  There is corn stubble on it right now.
>>
>>
>>
>> I am curious what others have found in these NLOS situations.  Because
the
>> obstruction is mid path, will the signal still be there next fall as it
is
>> now?  Are mid path obstructions on a long path better than obstructions
>> closer to one end?  Am I absolutely stupid for even considering this
>> install?
>>
>>
>>
>> I went over all the physics involved and told him of my experiences.
 Like
> I
>> said, he is motivated.  I told him I wouldn't tie him into a contract,
but
>> we'd go month by month and if we found later in the year it wasn't
> working,
>> we'd cut our losses.  He was OK with that.
>>
>>
>>
>> Since I respect the viewpoints of many of you, bring it on!
>>
>>
>>
>>
>>
>> Friendly Regards,
>>
>>
>>
>> Mike
>>
>>
>>
>> Mike Gilchrist
>>
>> Disruptive Technologist
>>
>> Advanced Wireless Express
>>
>> P.O. Box 255
>>
>> Toledo, IA   52342
>>
>> Mike's
>>
>
<http://www.tamatoledonews.com/page/category.detail/nav/5001/Local-Columns.h
>> tml>  Weekly Column
>>
>> 239.770.6203
>>
>> m...@aweiowa.com
>>
>>
>>
>>
>>
>>
>>
>>
>>
>
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