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Old 20-Sep-2014, 2:14 PM   #81
tripelo
Senior Member
 
Join Date: Jan 2010
Location: Dallas, TX
Posts: 139
Pete, that's a nice image of your vertically stacked HDB8-X antennas.

Quote:
Originally Posted by Pete Higgins View Post
... When I added a second HDB8-X to my TV tower array most channels signal strength improved 1-2 dB...

... but at least one actually appeared to get weaker?
Interesting.

There can be certain locations in elevation (height) where an antenna with an aperture that is small in the vertical dimension provides more signal strength than a larger antenna.

Could be that two (not-in-phase) signal fronts simultaneously arrive at different heights within the vertically spaced array (upper and lower portions of the antennas).

Maybe, analogous to the diagram posted earlier under the heading:

Stacked Antennas: Multipath & Diversity Gain?

The post, linked above, contains a drawing of stacked antennas and shows a direct wavefront (D) arriving at the lower antenna with a multipath wavefront (M=-D) arriving at the upper antenna. The signal summation would be less than the direct (D) alone.

A following post will show some measured signal variation versus height, likely the result of multipath.

.

Last edited by tripelo; 20-Sep-2014 at 3:43 PM.
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