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Coax termination and electrical theory explained.

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nuckolls.bob(at)cox.net
Guest

Posted: Fri Mar 07, 2008 7:43 am Post subject: Coax termination and electrical theory explained.

At 06:19 AM 3/7/2008 -0800, you wrote:



 	  Quote: 	
		  



I have been dabbling with the physics of current moving along a wire. One 

of the remarkable things about physics that I have to keep re-learning is 

that seemingly simple phenomena have wildly complicated reasons for 

working as they do. But understanding these reasons keep us on track .

You would think that the “theory” of electricity has been well worked 

out by now. But here’s your test:



   1)What carries the energy in a simple electrical circuit?

   a-Electrons,

   b-Holes,

   c-God knows!


	


   <snip>



 	  Quote: 	
		  Bob, in my humble opinion, needs a little nudge on this. Here's how NOT to 

terminate coaxial cable--



http://aeroelectric.com/articles/shldwire/shldwire.html



But yikes....! So it turns out that the simplest DC circuit operation is 

wildly difficult to explain, but basically the electromagnetic fields 

carry the energy, not the electrons. They are just there to move and cause 

the magnetic field. The electrons have only an electric field, and it is 

only the electrons movement through space that generates a magnetic field. 

If you followed alongside an electron, you wouldn’t see ANY magnetic 

field. This is the difference between static electricity and the regular 

stuff. Static electricity has no magnetic field because the electrons 

aren’t moving with respect to the observer.


	


   Eric my friend . . . you're making this far more complex

   than it needs to be. Yes, the physics of conducting electrical

   energy from one place to another have been studied, quantified and

   explained for a century or so. However, there ARE practical

   departures from "ideal" that do not materially affect performance.



   Super-simple VHF COMM antennas were installed by the tens of

   thousands in light aircraft using the technique illustrated.

   Yes, the effects on SWR, radiation patterns, and radiation

   efficiency were degraded from ideal . . . but the the

   ideal was never perfect either.



   For the frequencies of interest (118 - 135 Mhz), effects

   of the 1" or so of non-coaxial conductor that results from the

   use of terminals on pigtails was barely noticeable in the

   lab and never noticed by a pilot in an airplane. Now, the

   effects of this technique at transponder frequencies is

   much larger . . . easily measured in the lab. But with

   some judicious refinement of fabrication technique to

   get the shortest possible leads (below 1/2") the

   effects on real time performance were not observable.



   When we go to the lab to make calibrated measurements

   of performance, the obvious goal is to minimize the

   effects of test-setup error. In this environment we

   strive for the-best-we-know-how-to-do with the goal of

   suppressing sum of all test errors to less than 1/4

   that of the phenomenon being measured. But in the real

   world of talking to Flight Watch from an RV, well considered

   departures from the best-we-know-how-to-do don't reflect badly

   upon our craftsmanship.



   Bob . . .

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longg(at)pjm.com
Guest

Posted: Fri Mar 07, 2008 1:20 pm Post subject: Coax termination and electrical theory explained.

Holy cow, I just want to talk on the radio. I've got a plastic airplane so I just snip off the ends and throw them away. Radio works great - all 3 of them. You guys are splitting hairs over a stupid cable 8 feet long (if that). What are you flying, 747's? I'll bet my radio would send/receive just as well using some RJ6 leftover from my satellite installation. 



Do Not Archive



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henador_titzoff(at)yahoo.
Guest

Posted: Fri Mar 07, 2008 3:11 pm Post subject: Coax termination and electrical theory explained.

I hate to say this, but just because it works for you doesn't mean that it's going to work for everyone else.  I would follow the manufacturer's recommendations and even improve upon it if possible.

 

Henador Titzof



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