How do I read signal and noise ratings?
These numbers are given in decibels (dB) and are expressed as negative numbers. The more negative the number, the less strength it represents. Thus, -40 dB represents more strength than -70 dB. The values are logarithmic. A signal amplitude change of 3 dB is equivalent to a factor of two; 10 dB is a factor of ten.
Signal: (in dBm) A small negative number is good (-40 is good, -98 is bad)
Noise: (in dBm) A large negative number is good (-98 is good, -40 is terrible, -70 would be pretty bad in the real world)
SNR: (in dB) High is good (should be the same as difference between noise and signal, a difference of 20 would be great, a difference of 1 may barely work)
SNR(dB) = Signal(dBm) - Noise(dBm)
Signal Quality: High is good (somewhat like SNR but indexed to 100 with noise as the base, percentage of the best theoretical ideal quality in regards to your local-noise)
Signal - Noise = SNR
-82 - -98 = 16
Signal / Noise * SNR = Signal Quality
-82 / -98 * 16 = 13.4%
Typically, noise will be -92 which means you should get a clean connection with a signal as low as -92. However, expecting to hold a good connection with a signal lower than -85 (e.g. -90), is expecting too much. The signal can be improved by -3 dB by doubling the power setting at the transmitting radio, e.g., 100 mW increased to 200 mW would improve your signal from -85 to -82. Antennas with increased gain will also help. Say you had the standard 3 dB antenna and changed it for a 12 dB antenna, that's a 9 dB increase, so your signal would increase from -82 to -73 which would be an excellent signal, probably capable of 54 Mbps. Using the term excellent in terms of running a WISP, it would probably be only 3 bars on a 5 bar signal strength meter. Don't worry if, as a WISP your signal quality is low, like 14%. It's not really a problem since -82 is considered
