A stretch of garden hose (or several hoses connected together, or any other
length of tubing) makes an excellent elevation
measuring device. Lay it out along the ground with the ends sticking up in the
air. Water inside the tube will be at the same
elevation at both ends of the tube. Measure the height of the water in each
end above the ground and you will be able to determine
the difference in ground elevation. (You might need a ladder at one end if the
ground drops off quickly!). It only takes one
person (with a bit of care) to make the measurement.
At the opposite end of the scale, my all-time favorite high-tech field
measurement device is a special surveyor's GPS receiver.
The receiver not only measures the time differences between the various
satellites like every other GPS receiver, but also
calculates the actual wave front corresponding to the time ticks and then
computes the phase difference of the radio signals
arriving from each satellite. The resolution is about 1cm in 3-space, if I
recall correctly.
-- Eric K3NA
-----Original Message-----
From: owner-towertalk@contesting.com
[mailto:owner-towertalk@contesting.com]On Behalf Of Bill Ralston
Sent: 2001 November 28 Wed 20:08
To: towertalk@contesting.com
Subject: [TowerTalk] Transit Accuracy Statement Retracted
Back on 11/26 I made the statement that I was able to achieve "accuracy of
1/2 inch in vertical and horizontal" when laying out guy anchor points for
my tower. When asked how I knew this, I realized I don't. I was mistakenly
thinking that, since I could see the "stick" scale 80 feet away clearly
through the transit sight that I knew it was that accurate. Although I may
have that much _resolution_, the _accuracy_ is a function of how well the
transmit is pointed in azimuth and elevation.
For the particular transit I rented, the azimuth scale was calibrated in
degrees. Although it has some kind of vernier scale, I never figured out how
to read it. Hence, my azimuth accuracy was probably about a degree, or 17"
at 80'; a lot less than 1/2" (but fortunately well within the requirements
of the tower!)
For elevation, the level was quite sensitive. Based on the repeatability of
my measurements when I moved the "stick" I think it is probably accurate to
better than a foot at 80'. This is supported by previous (tedious)
measurements of the elevation differences that were done with conventional
level and agreed within about 6".
I have a newfound appreciation for how it is that you often find several
surveyer marks at the corner of a property, none of which seem to agree on
where the actual corner is!
(By "stick" I mean the big ruler that is held vertically by one person and
is viewed through the transit to read off elevation difference by the second
person).
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-----
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List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 100 feet for under $1500!! http://www.anwireless.com
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
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