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Old 14-Sep-2014, 7:30 PM   #79
tripelo
Senior Member
 
Join Date: Jan 2010
Location: Dallas, TX
Posts: 127
UHF Signal Strength vs Antenna Height (AGL)

In May 2012, Bob Nelson (forum member re_nelson) and I performed some experiments to observe the effects (in a suburban area) of UHF signal strength versus height of an antenna.

Signal strength measurements of 27 DTV stations versus receiver antenna height were recorded. On average, signal strength increased with height increase. Individual stations showed variability of signal strength (in a repeating pattern), this could indicate the presence of signal layering. Signal layering can result from reflections (ground or other) that either reinforce or reduce signal strength at various receiver antenna heights.

Location: Garland, TX

Signal Path: Line-of-Sight, about 28 miles from TV stations located at Cedar Hill, TX.

Local Clutter: Single story residential homes with some trees (approximately 30 45 feet tall). The LOS path was essentially between any tall trees.

Signal Sources:

At that time there were 27 DTV stations in the same general azimuth direction that could be received at this location. These 27 stations served as stable signal sources to compare strengths at various antenna heights.

Equipment:

Antenna: Terk HDTVi mounted to a push-up mast. The HDTVi was chosen because of its small aperture (allowing better height resolution), small size, and relatively flat response across the band. The HDTVi is shown in image below.

Mast: A push-up mast capable of being quickly lowered or elevated up to about 45 feet. The mast had numerical marks on it every foot for quick determination of height.

Signal Analyzer: Sencore 1456, capable of scanning the UHF TV band for signals and measuring and recording the amplitude and MER (quality).

Coaxial Cable: Fifty feet of commercial quad shield RG-6 with custom connectors.





Methodology:

Beginning at 15 feet AGL, measurements of all measurable* signals were taken at close intervals up to a height of 33 feet AGL. Most measurements were made at 1 foot intervals, between 18 and 24 feet, the measurements were made at 2 feet intervals.

* All stations had adequate signal strength, but some were low power (LP). For a few reasons, LP stations among several full power stations are difficult for an analyzer (tuner) to reliably decode. However signal strength measurements were feasible. The entire UHF TV band (Channel 14-51) is well represented by measurable signals.





Below is a chart showing the average signal level of 27 UHF channels versus height.





Each point in the graph represents that average signal strength of 27 DTV stations (RF channels) at that particular height (AGL). The averaging process takes out a lot of information, but does help provide an overall view.

The graph shows there is a signal strength plateau around 24 feet. But, increases resume at heights greater than 30 feet. Interestingly, the FCC uses 30 feet AGL for outside antenna in many propagation/contour analyses.

Much appreciation to re_nelson for his assistance, equipment, and support.

Later, the data illustrating signal strength versus height for individual stations can be graphed and posted, in a few weeks maybe sooner.

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Attached Images
File Type: jpg HDTVi _on Mast.jpg (37.4 KB, 3211 views)
File Type: jpg HDTVi _32 feet.jpg (193.6 KB, 3261 views)
File Type: gif UHF Signal Strength vs Height.gif (8.9 KB, 3573 views)

Last edited by tripelo; 20-Sep-2014 at 2:04 PM. Reason: typo
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