I won't claim any great expertise here, but I have seen the same from RM. There is some minor thing wrong with the way Fresnel is calculated that seems to cause this.
If you leave the link right as it is, but change the overall size of your map, you may find that the odd up and down rssi calculation goes away. It has worked for me before. ++++++++++++++++++++++++++++++ Neofast, Inc, Making internet easy 541-969-8200 509-386-4589 ++++++++++++++++++++++++++++++ -------------------------------------------------- From: "Fred R. Goldstein" <fgoldst...@ionary.com> Sent: Monday, August 30, 2010 12:34 PM To: "WISPA General List" <wireless@wispa.org> Subject: [WISPA] Slight variations in antenna height, big path loss change > I'm doing some path loss estimates in RadioMobile. Mainly 5.8 GHz stuff. > > I have a place where I'd like to run a point-to-multipoint sector as > an injection feed to multiple APs in the mesh. This would need to > run AirMax or Nstreme or NV2 in order to manage the traffic, but that > part seems easy enough. If I don't use NV2 and claim the SkyPilot > rule, then my ERP is capped at +36 dBm. (So I'm kind of marginal on > path loss already.) I can use a 20 dB sector antenna (AM2-60), whose > footprint covers all of the APs I'd like to reach, up to 22 > kilometers away. The APs are set to have 24 dB panel antennas. So > they can run "point to point" ERP upstream, to the extent that it > helps the fade margin in that direction. BTW the paths are mostly > over water, but elevated by more than 2-3 Fresnel zones. > > Now here's the weird part. In RadioMobile, when I adjust the PtMP > end's height in half-meter increments, path loss jumps all over the > place. To one destination 18.5 km away: > At 7 meters, 134.5 dB. At 7.5 meters, 144.7 dB. At 8 meters, 139.3 > dB. At 8.5 meters, 134.4 dB. At 10 meters, 137.0 dB. > > Now to a different destination only 12.5 km away (the closest one), I get: > At 7 meters, 137.4 dB. At 7.5 meters, 150.7 dB. At 8 meters, 132.2 > dB. At 8.5 meters, 131.7 dB. At 10 meters, 136.5 dB. > > Well, the obvious answer so far might be to avoid the 7.5 meter > height, but now going to a third destination 16.8 kilometers away, I get: > At 7 meters, 141.6 dB. At 7.5 meters, 134.3 dB. At 8 meters, 136.6 > dB. At 8.5 meters, 139.5 dB. At 10 meters, 151.9 dB. > > So there's no height that makes everyone happy, and that assumes I > actually get a choice of height. Most likely it goes on the power > pole wherever they let us attach it. And tweaking the remote ends > doesn't make that much difference at all. > > So here's the question. Is this type of variation likely to exist in > the real world, or is this just RadioMobile's propagation model being > overly sensitive? Thanks! > > -- > Fred Goldstein k1io fgoldstein "at" ionary.com > ionary Consulting http://www.ionary.com/ > +1 617 795 2701 > > > > -------------------------------------------------------------------------------- > WISPA Wants You! Join today! > http://signup.wispa.org/ > -------------------------------------------------------------------------------- > > WISPA Wireless List: wireless@wispa.org > > Subscribe/Unsubscribe: > http://lists.wispa.org/mailman/listinfo/wireless > > Archives: http://lists.wispa.org/pipermail/wireless/ -------------------------------------------------------------------------------- WISPA Wants You! Join today! http://signup.wispa.org/ -------------------------------------------------------------------------------- WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
