HI Guys,
Greetings from N6IJ.
Good suggestions for checking plumb.....An additional
tip: If you use the
old transit that you've had kicking around in the garage for the last 20
years, (or any non-electronic theodolite, for that matter) you should
account for possible instrument mis alignments. Try not to kick the
transit....used to be hundreds of dollars at an instrument repair shop, to
adjust an instrument.... Surveyors used to do this for all measurements
before the era
of Electronic Theodolites, or Total Stations. (Them Japanese instrument
manufacturers are really good!) If the plates of the transit are not
precisely level, or the telescope supports do not exactly keep the
pivoting axis of the telescope level and parallel to the bottom plates,
then the plane defined by a vertical rotation of the telescope is not
vertical. Could be out possibly a significant amount. You can check this
by sighting the center of the base of the flag pole, or tower, pivoting
the teleescope up to the
top, and choosing a identifiable mark on the pole which can be
relocated, that lies exactly on the crosshairs. Flip the gun (telescope)
180 degrees, and rotate the base plate 180 degrees, and do the same thing.
The high point should fall exactly on the crosshairs again. If not, then
visually remember the location of the first and second (High) shots,
using precisely the same base shot reference, and
the true plumb line is halfway between them....Another thing about old
transits is you should point it to the sky, and adjust the eyepiece, which
usually rotates for focussing, and get the crosshairs in precise focus.
It they aren't, then you will notice that the target you point at, will
have apparent motion across the crosshairs with your eye movement behind
the objective (eyepiece) lens... making precise measurements difficult.
73, DX de Pat, AA6EG/N6IJ
"The Contest Station from the Government"
Marina Amateur Radio Contest Station; N6IJ
599 DX Drive
Marina CA 93933
aa6eg@tmx.com
On Wed, 13 May 1998, K7LXC wrote:
> In a message dated 98-05-12 23:53:54 EDT, garyk9gs@solaria.sol.net writes:
>
> > How does one properly plumb a continuously tapering pole, like a flag pole?
> >
> > A plumb bob hung from the top won't easily work, unless you look for equal
> > deflections on several points around the circumference of the
> > pole.....very difficult to manage.
> >
> > Obviously, a spirit level is out too.
>
> Commercial installers use a transit and sight in at the midpoint of the
> bottom section. Then you tip the instrument up and sight up the pole. If the
> sight isn't in the middle of the pole at the top, the difference is how far
> out of plumb it is. You need to do this on two different faces to get it
> plumb.
>
> Actually we have used a plumb line inside of cellular monopoles. Then you
> level it with the base nuts.
>
> Cheers, Steve K7LXC
>
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