[TowerTalk] measuring F/B

[Tom Rauch]

From:           	K7GCO@aol.com
Date sent:      	Wed, 30 Aug 2000 04:23:23 EDT

>   The major flaw with ground wave measurements is the earth greatly 
>   attenuates horizontally polarized signals, while vertically polarized
>   signals have much less attenuation.  Because of that, any feedline
>   radiation or scattering has an exaggerated and unpredictable influence
>   on results.

**** The proper design of a feed and matching sytem would eliminate
that variable and make a legitmate test.  

Not true at all. The feed system has nothing to do with scattering 
errors. Scattering errors are cause by re-radiation from other media 
around the antenna under test, or in the test path. 

>  Do you have a source or actual test data for that comparison of
>  polarization 
> losses statement that has I confess evaded me somehow. 

It's in any textbook on antennas. A horizontal electric field is in 
effect "short circuited" by any conducting media in the same plane. 
A vertical electric field is not, because it is at right angles to the 
conductive media.

> Vertical polarization has such a "Severe Ground Reflection Conflict" at
> low angles over ground that it acts like horizontal polarization for about
> 6 degrees creating a null just like the 180 degree phase shift of
> horizontal polarization does.  It's called the "Persudo Brewster Affect". 
> Horizontal polarization doesn't seem to have any "Ground Reflection
> Skeletons" in it's closet.  Salt water chases the "Dyslectic Bad Spirits
> of Vertical Polarziation" away, it acts "Text Book Normal" as if it was
> "Liquid Copper" and even all those ideal patterns in the text books
> printed on non-conductive paper--are for real.  

I'm speechless. I had no idea "bad spirts" were involved.
 
> Would you believe that vertical polarization can create a pattern so low
> on salt water it kicks up a perceptible Mist--"RF Mist" that is.  You can
> see with special (you guessed it) "Polarized Glasses" the vertical pattern
> of the antenna and it also leaves a white salty pattern on the salt water
> almost like Crop Circles.  Unfortunately it doesn't do this on fresh
> water.  These visual patterns are a great aid to antenna testing.  The
> glasses can only see one polarization at a time and you just have to
> rotate your head 90 degress to see the other or 45 degrees for 45 degree
> polarization.  There is a circularly polarized lens in photography to be
> compatible with modern range finders.  This type of "RF Visual Filter"
> could be of great aid.  That's an absolutely true story.  I just made it
> up.

I always wondered what caused crop circles, now I know. What a 
wonderful learning tool internet has become! (Rest of education 
deleted.)


73, Tom W8JI
w8ji@contesting.com

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