On 11/16/2013 2:04 PM, Jim Miller wrote:
Light scatters as a function of wavelength and particle size to interact
with. You see the results of scattering when you look on the horizon and on
one day see a white haze which is scattering off water and other large
molecules for all visible wavelengths (hence white) and on other days it
may be blue to the horizon where that wavelength is scattering strongly off
oxygen molecules strongly vs longer wavelengths.
Take some photos of the horizon from a ridge line or from a few
thousand feet from an older small airplane using B & W film.
The windshield and windows in older planes were not UV protective
and B & W film is sensitive to UV light. Take photos with color
film as well. Compare the results. Quite often you can not see,
or barely make out the horizon in the B & W photos and it will
only be a bit hazy in the color shots. That haze in the B&W shots
is from the UV light. .
Pilots flying those old airplanes at 10,000 feet could get some
really bad sunburns wearing a short sleeve shirt, Course some
would take their shirts off to get a fast tan, but usually got burnt.
Those planes might have had a 1/8th inch windows although I think
some were only 1/16th.
Mine had a 1/2 inch windshield with 1/4" side windows that were
UV protected and tinted. It gets pretty bright up there above the clouds..
Exposure increases about 10 to 12% per 1000 feet.
BTW, reflections from new snow can double the UV exposure. I don't know
about sand, Google is your friend,
73
Roger (K8RI)
UV continues this strong scattering behavior with oxygen molecules.
Anything that gets past the ozone layer will repeatedly scatter with little
absorption resulting in it coming at you form all angles regardless of
attempts to screen the direct sunlight. The first order criteria for
resulting exposure is the amount of horizon you can see whether "in the
shade or not."
Jim ab3cv
On Sat, Nov 16, 2013 at 11:34 AM, Patrick Greenlee <patrick_g@windstream.net
wrote:
Larry, It is basically an intensity and exposure time issue. I sunburn
easily. I can attest to getting a sunburned forehead while wearing a big
brimmed hat while fishing. The reflected UV can be quite powerful. Often
reflected intensities are less than direct by quite a margin but can still
be sufficient to accelerate deterioration. It is a matter of the nature of
the reflecting surface and its orientation that determines the percent of
light that is reflected. Chemical change (what we call deterioration) is
accelerated by elevated temperatures. Heat and light are both factors in
deterioration and don't forget smog or reactive atmospheric components
like ozone etc. In general the higher the temperature the faster the
chemical reaction. Similarly the brighter the light the faster the
deteriorating effect.
Light when absorbed heats the object but that isn't why UV is a
significant player in deterioration. The energy in a quanta of light is
dependent on the wavelength (color.) E = h nu (I spell the Greek lower case
letter nu as it isn't on my keyboard and I don't know how to get it or if
it is available in the extended character set supported by Windows.) OK, in
the above formula E is energy, h is Plank's constant, and nu is the
frequency. It is easily seen that the higher the frequency the more
energetic the photon. From red to blue is an increase in frequency. Ultra
Violet is bluer than blue, higher in frequency and more energetic. The UV
knocks the electrons of some atoms into higher orbits than they usually
achieve this stores more energy than normal and releases this energy when
they return to their ground or original state. This energy is what makes
for energetic photochemistry. Think of it as UV supplying the energy of
self destruction as well as catalysis of oxidation.
Light is quantized in photons. Each UV photon has a probability of
causing damage to a susceptible material Bunches of UV causes bunches more
damage. There is not a lower intensity threshold below which UV does no
damage. Less UV does less damage but each photon has the sane damage
causing potential so it is a pure numbers game where less is better for
survival of susceptible materials.
Executive summary: Light usually good, UV often bad.
73
Patrick AF5CK
-----Original Message----- From: Larry Loen
Sent: Saturday, November 16, 2013 9:41 AM
To: Patrick Greenlee
Cc: TowerTalk
Subject: Re: [TowerTalk] Bundling of tower coax and control lines
Good thoughts from one who has been there.
Question for you: Is direct sunlight more important than the reflected
kind? I seem to remember that you can get sunburned from reflections off
of sand just as direct sun. But, I also know that UV tends to be absorbed.
I'm wondering if it helps at all to simply get stuff out of the direct
sun. I suppose there will still be some UV from reflections off of the
sand, but I also wonder how much the intensity goes down when you expose
yourself only to that. Longer is longer however it is achieved.
Do you know?
WO7R
On Sat, Nov 16, 2013 at 7:40 AM, Patrick Greenlee
<patrick_g@windstream.net>wrote:
Larry, the canvas is a good idea and it can be painted as well to extend
its life. Good UV resistant house paint will do the job. I have seen old
used canvas hose used to protect cables. I remember the problems I had a
few decades back with my mom's south facing wooden entry door at Bull Head
City Arizona. I never found a coating (paint) that lasted more than a
couple years at best. The intense sunlight with strong UV components and
elevated temps can be difficult to deal with. I'm currently looking for a
thin flexible tubing (round or flat on a roll) that is UV resistant and
flexible when cold. Simple criteria but difficult to satisfy on a moderate
budget.
73 and best of luck to you.
Patrick AF5CK
-----Original Message----- From: Larry Loen
Sent: Saturday, November 16, 2013 8:05 AM
To: Patrick Greenlee
Cc: TowerTalk
Subject: Re: [TowerTalk] Bundling of tower coax and control lines
I live in the low Sonoran dessert (1400 feet above sea level) and UV is
something we worry about around here.
My stuff is too new at about a year in place, but I am wondering a bit
about some of my setup. I have an MOV box that is discolored (no other
problems; no cracks, etc.) and I have some exposed PVC conduit that is so
far unchanged, except for one slightly darker elbow.
The Home Depot actually suggested that ordinary paint could prove to work
well for cables. I haven't tried that one yet. Maybe it buys an extra
year or two before the paint cracks?
I am also wrapping some of my ground level cable in canvas. I figure that
it is thick enough to block it. If the canvas dies, it would be cheap
enough to replace.
I haven't though about what to do about the cables hanging from the tower.
I was kind of resigned to replacing them eventually. My tower is a
crankup
and it seems to me that the whole question of covering them with anything
is problematical. If you come up with an answer, I'd love to hear it.
Larry WO7R
On Sat, Nov 16, 2013 at 6:24 AM, Patrick Greenlee
<patrick_g@windstream.net>wrote:
Roger, Your UV is not nearly the intensity of the 5000 ft high desert
QTH.
What works for you will not work with the intense UV of the high desert.
Ray, I think the dripline is something to consider. I think it should be
much more survivable than typical water hoses which the UV eats quickly.
I
have had HD clear plastic tubing turn to sticky goo in under a year. I
have
used some 1/2 and 3/4 inch black plastic tubing in drip systems and it
lasted with no apparent damage for several years. The black plastic wire
covering "tubing" (wire loom) with a slit on one side lasts for several
years. I always found it necessary to put some tape around it every so
often or to use a few distributed tie wraps to keep the enclosed wires
from
popping out when the bundle was flexed. Maybe you could ferret out the
mfg
and buy it in longer lengths that the shorter ones at the auto parts
store.
Patrick AF5CK
-----Original Message----- From: Roger (K8RI) on TT
Sent: Saturday, November 16, 2013 2:27 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Bundling of tower coax and control lines
On 11/16/2013 2:51 AM, Ray Benny wrote:
The subject of bundling tower coax with a spiral/twist type material was
recently mentioned. I cannot seem to find it.
I would like to bundle my coax and other cables, hanging from coax arms,
to
protect them from UV rays. My QTH is high desert, almost 5000 ft
elevation
and control lines on other towers are starting to be affected. I used
non
UV resistant cables that I had on hand at the time,
My Opinion:
Because of the cost and work involved, I'd choose to just replace the
cables.
There are very few coax cables and rotator cables that are very
sensitive to UV.
The only brand name coax sensitive to UV "that I know of" are the
UltraFlex versions of the LMR series.
I do have "old" rotator cables that the outer jacket is failing after
nearly 30 years.
If the cables have been up long enough to already show substantial
deterioration, it's time to replace them anyway.
73
Roger (K8RI)
Does anyone have leads to locate some of this UV resistant material?
I've
seen this type of material for indoor cables, in 6 - 8 ft lengths. I'm
hoping someone makes long lengths, 50 ft or so and of different
diameters.
Just a thought, has anyone successfully used large diameter black water
drip line for this? Seems to cover 2 RG8 size coax cables, a #12/2
copper
line and a 3/8" control line would require at least a 1" diameter line.
Tnx,
Ray, N6VR
Chino Valley, AZ
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