I think that is the reason they use the first peak going up the tower. That minimizes the difference in time of arrival of the ground reflected signal vs the direct signal. I understood that each channel had several peaks at different heights on the tower, but using a peak up higher would give you a lot more difference in Time of Arrival between the ground reflection and the direct path.
Also, I understood that using a higher on the tower peak was not as stable a point as the lowest one. All this is from the tech doing the installation, and of course, he may have known how to set it up without understanding why he was doing it. 73 - Jim W5ZIT --- On Sat, 8/9/08, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote: From: [EMAIL PROTECTED] <[EMAIL PROTECTED]> Subject: RE: [Repeater-Builder] Height Gain figure To: [email protected] Date: Saturday, August 9, 2008, 8:36 PM At 8/9/2008 17:58, you wrote: >I watched a cable TV system installation on a 300 ft tower many years >back, and it was interesting to see where the receive antennas were >placed. We had channels 4,5,8,11, and 13. > >The tech took a portable antenna and receiver up the tower and watched the >signal strength for each channel as he climbed, and placed a marker on the >tower for the FIRST peak he found in signal strength. He started on ch 4 >and that antenna position was at about 100 ft. We were about 70 miles >from the TV stations. > >As he worked his way up the channels the ch 13 antenna wound up at about >200 ft. All these points were at the first peak he found going up the >tower. As he climbed above that point, the signal strength would go down >for a given channel, as the ground reflection was starting to cancel out >the direct signal, or was no longer adding to the direct signal, whichever >way you want to look at it. > >I thought this might be interesting to the group - Yes. But what about multipath? Ground reflection "adding" to the direct path can result in severe ghosting. Bob NO6B ._,___
