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Old 07-22-2008, 07:19 PM
JoelW JoelW is offline
Junior Member
Join Date: Apr 2008
Posts: 14
Default Longley-Rice vs Pathloss diffraction algorithm

I just compared a challenging UHF path in Pathloss with the same path in Radio Mobile. Pathloss showed it as being a good path, with about a -81 dBm Rx level. Radio Mobile instead showed a -100 dBm level. Radio Mobile uses the Longley-Rice algorithm, no choices. Pathloss by default uses the "Pathloss" algorithm.

The difference between these two is dramatic, enough so that if I were to recommend this path (trusting Pathloss) I'll guess that my customer would be very unhappy with me. There's a 200 foot tall hill about 80% of the way along the path that sticks up like a sore thumb and is the cause of the trouble.

Two questions:

- Does anybody have a good reason for why the two calculations would provide such dramatically different results? (19 dB!!)

- Should I be running all my paths using two or three algorithms, and then using the worst-case result? How do I decide which to go with?

Yes, I have read the brief discussion on this topic in the Pathloss manual. It's so short that it's clearly meant for people who are already path study experts. What I need is some good clear discussion on the topic. (that hopefully won't require me to lock my office door for 6 months and study the topic at a PhD level)


Last edited by JoelW; 07-22-2008 at 07:30 PM.
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