[TowerTalk] Advice Requested

[Pete Smith]

At 06:49 PM 6/20/03 -0700, Jim Lux wrote:
>Dacron fishing line works as an invisible guy... even something like nylon
>seine twine would probably work, and not be overly visible.
>Human eyes can resolve about an arc minute, so you can figure out how small
>something needs to be to make it invisible, given the distance (... about
>1/4000th of the distance, so 100 ft away, it needs to be 1/40th of a foot or
>smaller... 1/4" give or take)


Unfortunately, this isn't the whole story.  I can see the 3/16" EHS guys on 
my tower from over 200 feet away.  Super good eyes?  Nope -- it isn't a 
matter of your eye actually being able to resolve the width of the guy 
wire, but rather the contrast between the color and/or brightness of the 
guy and the color and/or brightness of the background.  The result is that 
the "pixels" through which the guy wires pass have a noticeably different 
*average* color and/or brightness than those adjacent to them, so you can 
see the wire even though it is too small to resolve.

I didn't used to believe this until I saw 30-meter-resolution satellite 
photos of the causeway across Lake Pontchartrain that clearly showed a 
roadway whose width was much less than the system resolution.

Bottom line is if you want it not to show, you need to match it to the 
background as well as you can.  I've seen a 75-foot tower with TH7DXX that 
you had to look three times to resolve against the forest background 
because of a carefully applied coat of brown-grey paint.


73, Pete N4ZR
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