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#41
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Vertical problem
Funny, I've seen no one recommend addition of a 1:1 choke balun near the antenna feedpoint. If RF is flowing back down the shield of his feedline, that surely could cause some incorrect readings on SWR in the shack, wouldn't it? K7AAT And, how well would rf flow back down the shield of "buried 75 foot of RG213..." ? :-) Jonesy Apparently well enough to cause a problem. Its now 9 days later from the above comment, and I see today that the original poster followed my suggestion to install a balun which has solved his problem. Ed K7AAT |
#42
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Vertical problem
Ed wrote in
. 192.196: .... Apparently well enough to cause a problem. Its now 9 days later from the above comment, and I see today that the original poster followed my suggestion to install a balun which has solved his problem. Ed, that defines how you define the problem. If the problem was different measurements, that was caused by disturbing the thing that was measured. The different measurements hints another possible problem, common mode feedline current. The baluns have changed the effect of those, and probably differently at different frequencies. But fundamentally, it is wiser to preserve the common mode current path (even if you reckon the baluns help to reduce it) when making the measurments. The whole exercise demonstrates that the measurements from shack were valid, it was disconnecting the feedline and making measurements at the feedpoint that was invalid. (BTW, the measurements in the shack should be done with the shield path connected as normal.) A good example of the limited thinking in the proposition that you can only make valid measurements at the feedpoint. Owen |
#43
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Vertical problem
Cecil Moore wrote:
Michael Coslo wrote: Well, I don't think we can cover the entire earth with water past the height of the tallest mountains. Like that ever happened tho'. The original languages, like our own version of English, had numerous definitions of "earth". I can cover the "entire earth" in my handful of earth with a pint of water. At the time of that original tale, man had absolutely no concept of a 8000 mile diameter "planet earth". "Earth" was as far (and as flat) as one could see and I have seen Texas floods, in my lifetime, where nothing but water could be seen. :-) Heck, I have been sailing on Clear Lake, out by NASA, when I couldn't see anything but water in all directions. Absolutely. No question that the great flood was a localized phenom. I was just getting in my occasionall dig at those who would demand that since it says so in one book, it had to have been the world. The bible is mostly enjoyable reading as long as we don't get tripped up on the whole literal thing. - 73 de Mike N3LI - |
#44
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Vertical problem
On Sat, 02 Aug 2008 17:18:52 -0700, John Smith
wrote: John Smith wrote: JosephKK wrote: ... 95% plus of the transmitter or received energy is safely contained between center conductor and shield. That is how the physics works out. All of the feed line center conductor current is pretty well matched by the same current in the shield. It is the closely coupled concentric magnetic fields that make coax work so well. Or, simply put, for ever action, an equal and opposite reaction occurs ... yes, basic physics ... however, what is in question--since the other braid has and "inside" and an "outside", where does that equal opposite reaction occur ... Regard, JS Gawd, I am getting hasty in my old age ... No electrical field can occur without a magnet field, no magnetic field can occur with out a corresponding electrical component, again, basic physics; you are attempting to say the magnetic component of the current on the outside of the braid is NOT SEEN by the center conductor ... that may be in error ... but, I would be willing to listen how tinned copper (the braid) is some sort of shield to magnetic fields ... Regards, JS Faraday cage. |
#45
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Vertical problem
JosephKK wrote:
... Faraday cage. Form a wire loop inside a Faraday Cage; Wave a strong neodymium magnet about, outside the cage; You WILL get a reading ... http://en.wikipedia.org/wiki/Faraday_cage .... but, for electrostatic fields, they are dynamic. Regards, JS |
#46
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Vertical problem
JosephKK wrote:
... Faraday cage. Perhaps this will help: http://www.lessemf.com/faq-shie.html#Lead-Copper Regards, JS |
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