Wi-Fi Calcs

Over the last few months, I’ve been chicken scratching my RF calculations on the fly for customers, but it wasn’t until recently I stumbled across two xls-based calcs that were set up right to let me quickly fudge and tweak numbers to find sweet spots in power, transmit power, distance, fade margins, etc.

• Fresnel Zone Calculator
• RF Link Budget Calculator

People don’t just don’t realize just how far wi-fi can go (provided that spectrum isn’t already cluttered, which it often is).

For example, put a 23 dbi panel antenna on one of our both ends of our BelAir radios using one of the 11 outdoor channels available on 802.11a, and assuming a 1 dB cable loss on each end with 23 dB output power, and you get the following modulation rates with a 12 dB fade margin as your safety net.

54 Mps (-71.4 dbm) - 5.4 miles
48 Mps (-73.4 dbm) - 6.8 miles
36 Mps (-78.4 dbm) - 12.0 miles
24 Mps (-81.4 dbm) - 17.0 miles
18 Mps (-84.4 dbm) - 24.0 miles
12 Mps (-86.4 dbm) - 30.2 miles
9 Mps (-88.4 dbm) - 38.1 miles
6 Mps (-88.9 dbm) - 40.3 miles

If you want to be sure on areas with low fade margin, just put two of our radios on both ends of the long shot, and set the antennas with opposite polarization. Plug the radios into a good layer 3 switch, and the RSTP algorithm on our radios will take care of everything should one of the links go bad.