The old VHF TV antennas were horizontal and deigned to detect horizontally 
polarized signals.At VHF frequency the air press changed with height and at one 
wavelength the signal bent down.Over the horizon reception was possible with 
VHF.  The wavelengths of the new HD UHF signalsare to short to be effected by 
atmospheric air pressure and do not bend down.
I was working to get a HD signal for a friend with an amplified antenna in her 
attic.  I could not get PBS which was about 40 miles away.  I built a yagi 
director and put it in front of this square antenna, no luck.  Then I turned it 
pick a vertically polarized signal.  Yurka,  the station came in.   Why was I 
only receiving vertically a polarized signal?  I believe that they transmit 
horizontally.   Did it have something to do with the bruster angle, like the 
reflection off of a puddle that polarized sun glasses block?
I think I have now figured it out.  Vertically polarized signals have no 
height, just a width of one wavelength.  They can stretch out in the vertical 
direction and then be effected by air pressure.  To the TV folks know this?  If 
so they should transmit all of the transmitter energy vertically polarized.
Can I design a special antenna to capitalize on this effect?  It would be 
several wavelengths long in the vertical direction.
The things I find out by doing favors for others.
Frank

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