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 hot or cold !!! 
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Post hot or cold !!!
Operating Temperature

yes thats right OPERATING TEMPERATURE.

I was musing over a few antenna designs tonight and happend across a military supply site who gave among there specs for antennas Operating Temp -30 to 55°C ambient

I dont expect to subject my antenna to the +/- figures stated but what if any side effects will there be to the performance of an antenna at high or low temperatures

more over could you expect to see a difference in performance from say a 10 element 2mt beam in 30c and then operating it at say -5c

food for thought anyone....!! :?:

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Mon May 24, 2010 8:45 pm
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 hot or cold !!! 
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it MAY have something to do with any expansion /shrinking of components on the antenna with "extreme" temperature change changing the characteristics..


you may have a quarter wave vert on 40m shrinking and resonating on 10 during winter :lol:

billy

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Mon May 24, 2010 8:59 pm
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Post Re: hot or cold !!!
hmmm
an antenna for all seasons

I will use the main vertical during the summer months for the lower bands but as winter approaches and it contracts you will find me on the higher bands

but in all seriousnes if it is an expansion / contraction thing then the use of say stainless steel screws jubilee clips which will expand less then the aluminum they are holding together are going to take there toll sooner or later.

also the effect of say the collar of a pl plug or n type that is subject to our seasonal temp variations (This year has seen lows of -15c in leeds and it was +26c at the weekend) the collar not mating to the same material would i expect for some kind of variation..


my head hurts

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Mon May 24, 2010 9:13 pm
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Silent Key

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Post Re: hot or cold !!!
If I've got my sums right, a total variation of 85°C would mean a change in linear dimensions of 0.2%. That would equate to a shift in centre-frequency of 290kHz on 2m and 860kHz on 70cms. I guess that might make a difference if you had a very narrow-band antenna but I can't believe that's the main issue.

The temperature would probably be much more of an issue on ancillary bits and pieces like traps, connectors, coax, fixings, or something like a balun which is being run close to its thermal limits.

Billy: the sums don't quite support your neat idea of a single antenna giving you 40m in the summer and 10m in the winter; but it would be a great unique selling point if you were to market one, and I've seen more outrageous claims than that in some antenna advertising ;)

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Steve G3TXQ


Mon May 24, 2010 9:20 pm
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Post Re: hot or cold !!!
Just a thought. But the expected operating conditions are to say the least going to be far less favourable to equipment in climates that are at the bottom & top of that temrature range.
Look at the bottom of page 91 of this months Radcom to see what low temperatures can do & for those who are not RSGB members it's an image of a vertical antenna that has been forced apart by water as it has frozen.
The given temperatures could thus suggest that the antenna is suitable for most operational situations, but that in very extreme conditions it will be operating at or beyond it's limit.


Mon May 24, 2010 9:52 pm
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G3TXQ wrote:
If I've got my sums right, a total variation of 85°C would mean a change in linear dimensions of 0.2%. That would equate to a shift in centre-frequency of 290kHz on 2m and 860kHz on 70cms. I guess that might make a difference if you had a very narrow-band antenna but I can't believe that's the main issue.

The temperature would probably be much more of an issue on ancillary bits and pieces like traps, connectors, coax, fixings, or something like a balun which is being run close to its thermal limits.

Billy: the sums don't quite support your neat idea of a single antenna giving you 40m in the summer and 10m in the winter; but it would be a great unique selling point if you were to market one, and I've seen more outrageous claims than that in some antenna advertising ;)

73,
Steve G3TXQ


slight exaggeration there steve on my part , i just meant shrinkage etc but tried to be a comedian with it ..

billy

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Mon May 24, 2010 10:29 pm
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m0lsx wrote:
Just a thought. But the expected operating conditions are to say the least going to be far less favourable to equipment in climates that are at the bottom & top of that temrature range.
Look at the bottom of page 91 of this months Radcom to see what low temperatures can do & for those who are not RSGB members it's an image of a vertical antenna that has been forced apart by water as it has frozen.
The given temperatures could thus suggest that the antenna is suitable for most operational situations, but that in very extreme conditions it will be operating at or beyond it's limit.


just looking at the opening post and it states a military supply site so this may well be the issue or part of as the army can be in all weather terrain so an antenna thats fine for a warm climate may not be adequate enough for the middle of Siberia to guarantee physical and electrical stability..

billy

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Mon May 24, 2010 10:33 pm
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Post Re: hot or cold !!!
In my experience temperature changes can cause problems cables either loosing flexibility when cold, and being damaged by cracking of the outer, in particular.
Some poor quality, pretend high grade, coax does this.
At very high temperatures you can get problems with dielectric and the centre core can migrate off centre.
We are talking extremes here and I have yet to see a problem with, what I would call "good quality products."

VHF Yagis can be detuned, to the point of being useless, by ice buildup.
Certain forms of matching methods are particularly prone to this with even heavy rain being a problem.

I've never been a fan of antennas with caps on the ends of the elements as, even though they are supposed to stop water getting in, you get a build up of water, possibly from condensation, when this freezes logic would say it forces the end caps out.
Sods Law says it splits the elements. :(
Lots of similar problems with antennas, and towers, because of water freezing inside structures.
I've seen triangular section towers with the legs split because the drainage of the legs failed.
When I worked in telecomms we frequently drilled drain holes in folded dipole.

Many commercial organisations use heating elements within the antennas to stop ice build up.

I've even seen lengths of scaffold pole hanging loose from a tower with a rope on the end.
The idea being, if you get an ice build up you pull on the rope and bang the scaff pole into the tower and the shock wave displaces the ice. :shock:

There should not be a problem with good N connectors as they are made to a high tolerances and, with two or three layers of self amalg they are reasonably protected.
PLs I would not know about as I can't think I've ever used them outside.

Cheers

Tony

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Tue May 25, 2010 12:09 am
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Maybe the manufacturer of the equipment has acheived the specs of one of the many DEF-STAN's, and one of these requirements is to be temperature tolerant?

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Tue May 25, 2010 6:31 am
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Post Re: hot or cold !!!
M0MGF wrote:
Maybe the manufacturer of the equipment has acheived the specs of one of the many DEF-STAN's, and one of these requirements is to be temperature tolerant?



You are right Jason, there will be a MIL Standard or DEF Standard which calls up the operating temperature and storage temperature and it is down to the mechanical stress, there may also be a humidity spec.

When we did the HPA's for the Type 45 frigates we had to meet significantly more stringent environmental specs than this including many G's of shock..., it was interesting protecting a TWT from this.

Cheers Tim M0AFJ


Tue May 25, 2010 7:38 am
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Silent Key

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Post Re: hot or cold !!!
Many years ago I was part of a team designing a remote tuner for use on the exposed roofs of embassies/consulates anywhere in the world. As you might imagine, the temperature specification was "challenging". FCO records showed that the consulate in Nicosia in August was the hottest of any of them.

It was a tough engineering challenge, but even tougher was having to spend a few weeks in Cyprus at Her Majesty's expense doing trials ;)

73,
Steve G3TXQ


Tue May 25, 2010 8:43 am
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