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Knife edge refraction in the 88-108 Mhz

J

joebtsflk1

Have a question about this topic...mountaintop xmtr is proposed to put out about 200 watts towards city of license. Xmtr would be at 8000', COL at 5400'. LOS to nearly all of COL except a half mile strip at the west edge of town where LOS is blocked by a 500' ridge. Xmtr is about 7 miles west of COL.

Would reception in the shadow totally crash and burn or would it be acceptable. Rest of COL is expected to be 70 dBu or greater, in fact even in the shadow L-R projections show 70 dBu plus, but not sure whether to beleive that.
 
joebtsflk1 said:
... in fact even in the shadow L-R projections show 70 dBu plus, but not sure whether to beleive that.
Click to expand...

If the obstruction really is a knife edge for the transmit frequency, then the diffraction loss will be close to 6 dB from the free space value of a clear, unobstructed path.

The diffraction loss over rounded terrain obstructions can be 20 dB or more.

The clip linked below may be useful...

http://i62.photobucket.com/albums/h85/rfry-100/FresnelClearance.gif

RF
 
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