Choosing a TV Antenna Mounting Site

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Trees & UHF

If a tree loses its leaves in autumn, reception behind it will improve dramatically.

In the following simulation, a tree is modeled as a perfect sphere blocking 90% of the signal.

Instantanous voltage diagram

Average power diagram

(The simulation was in 3 dimensions. The diagrams show the field strength in a plane through the tree center. Due to symmetry the diagrams look the same when viewed from above. The obstruction was coded as a disk, not a sphere, but the difference should be minuscule.)
(Please note the channel number and corresponding frequency used in these diagrams relate to U.S. channels, but are still relative.)

If the antenna is behind a tree, it is in overlapping fields: a weak field that passes through the tree plus a weak field that is diffracted around the tree. Overlapping fields are complicated, with strong spots and weak spots. This will be true even if the tree is not a perfect sphere. If you get a UHF antenna to work behind a tree, you will likely see dropouts when the wind blows because the strong and weak spots will move around as the tree deforms. Even in a good-signal neighborhood it is inadvisable to put a UHF antenna behind a tree.

The farther away a tree is, the less of a problem it is. For far away trees, assume no signal penetrates the tree, and reception will be by diffraction around the tree. Trees block 100% of satellite signals.

Trees and VHF-high (The tree blocks 60% of the signal)

Trees and VHF high

(Please note the channel number and corresponding frequency used in these diagrams relate to U.S. channels, but are still relative.)

In this case the wake tendrils are very broad. The tree is not likely to deform enough to cause a dropout. Reception might be slightly sensitive to wind.

Trees and VHF-low (The tree blocks 30% of the signal)

Trees and VHF low

(Please note the channel number and corresponding frequency used in these diagrams relate to U.S. channels, but are still relative.)

An antenna in its wake will work fine for channels 2-6.

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