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Puzzling SWR/Dummy load issue

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  #9  
Old 01-27-2009, 03:09 PM
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Beetle's Corollary: "If it ain't broke, fix it 'til it is."
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Old 01-28-2009, 05:32 AM
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Quote:
Originally Posted by Beetle View Post
Beetle's Corollary: "If it ain't broke, fix it 'til it is."
Damn Beetle.....I'm begining to think you're my long lost little brother the Dingo stole.......
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Old 01-28-2009, 05:43 AM
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Check velocity factor and jumper length, make sure the sign waves aren't cut off in mid SWR's. LOL.

Any who, good luck.
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Old 01-28-2009, 07:41 AM
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Just a couple of things, not all that important, but sort of handy to know every now and then.
These are all "of course it does" thingys.
Migration. It typically takes longer than you might think, and requires the cable to be put under more stress than is normal, sometimes a lot more stress than 'normal'. That's why you don't want to coil it up too tightly. It isn't exactly the most common thing to find, but if you take a look at the 'end' of a spool of coax, that tube it's wound on is the smallest the manufacturer thinks the stuff can be bent safely. Different sizes for different coax types.
Foam dialectic coax bends easier than the solid dielectic stuff does, but migrations also 'happens' easier with it, that foam just isn't as dense as the solid stuff.
If you have to make a sharp 90 degree bend then make a loop to sort of 'smooth' that sharp bend out some. It pays in the long run.

If applied power is enough to cause enough heat to affect coax to any extent at all, it's too much. It's a fairly safe bet that if that kind of heat is present it'll show up in other things around that coax, or connector. That dummy load is gonna start boiling, leaking stuff out the vent.

Wearing out coax is more a mechanical thing than electrical. The mechanical thing takes a fair amount of time, sort of. If there's an electrical 'wearing out', it's gonna happen sort of quickly. You can fix a mechanical 'wear out' in some cases. You're stuck with whatever electrical 'wear out' happens, ain't no fixing it, sort of. I have a problem with thinking of wearing out in terms of electrical stuff. I've found that electrical stuff wears out very quickly, with a bang in some cases. One of those it either works or it don't thingys. That's a personal foible though, not exactly something to make a big deal about.

And then there's the old "S _ _ _ Happens" thingy. No particular rhyme or reason to it, it just does. "I've used that thing for over 63 years, why'd it quit now?"... you know? Oh well, "S _ _ _ Happens"...

- 'Doc

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Old 01-28-2009, 01:21 PM
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How about if you yank and bend the coax while monitoring the SWR?

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Old 01-28-2009, 02:28 PM
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Tried that and the SWR didn't seem to jump around at all. Maybe some slight movement, but nothing drastic.

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  #15  
Old 01-28-2009, 02:47 PM
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You can if you want to, you have my permission. 'Course, that and a quarter won't make a phone call anymore...
- 'Doc

And a little more seriously, if wiggling coax makes the SWR change, you know you got problems somewhere. Typically not where you are holding the coax though, probably much more likely at the 'end' of that coax. 'Yanking' coax is sort of like a mini-coax 'stretch'. Not good. Almost always will produce some kind of change, very seldom a good one. Also why it's a good idea to support a long coax run in a couple of places, not just let it droop or hang there.
A small monkey might get away with swinging on coax, but Tarzan would bust his... when that '259 turned loose...

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