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.
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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>>>>
>>>>
>>>>
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>>
>>
>>
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