Which Frequency Band to Use?
How does a one choose 2.4G vs 5.8G or perhaps even 900 MHz?
Like most things there are trade offs. If there is an established network in your area that you want to connect to the choice has already been made for you. You need to use what they are using. If you are starting a new mesh network or the existing network is using more than one band, things get more complicated. Some things to consider include needed range, available elevation, antenna installation and desired data rate. Here is a summary of the merits and shortcomings of each WiFi band. BBHN firmware supports all three bands with a variety of radios.
Inexpensive gear available. (WRT54), lots of antennas available too.
Less Path loss. About 6 dB advantage compared to 5.8G over a 10KM path.
Although only very short lengths of feedline should be used, losses are much less that at 5.8G
Slightly more tolerant to less than perfect LOS
Noisy band. Interference from part 15 devices, microwave ovens etc.
Only a few 20 MHz channels available (Ch 1 and 6)
Slower data rates typically compared to 5.8G
High gain antennas are larger and heavier than 5.8G
Usually much quieter band that 2.4G or 900 MHz.
A lot of spectrum is available. Several usable channels in the ham band.
Higher data rates possible.
Higher gain antennas are available and smaller, lighter, cheaper than for 2.4 or 900
About 6 dB penalty in path loss for a 10 KM path compared to 2.4 (compensate with more antenna gain)
Very unforgiving of less than perfect LOS including Fresnel Zone clearance.
Feedline and connector losses high.
No cheap WRT like radios on this band.
6 dB less path loss per 10KM than 2.4G and 12 dB less path loss than 5.8G.
Penetrates trees and minor obstacles. This is a big deal where LOS not possible.
Much less feedline loss. Short runs of low loss coax feasible.
Noisy band generally. Especially in urban environments.
Limited spectrum and bandwidth
Low data rates.
Lower antenna gains and larger, heavier and more expensive antennas.
On many larger wireless network deployments the back-bone of the network is done with high sites using 5.8G radios and the last few miles is done with 2.4G gear. But this is not cast in stone. Other networks are built with only 2.4G or 5.8G equipment. Still others incorporate a mix including 900 MHz links for sites that have poor LOS and can tolerate lower data rates.
addendum: 9/16/19 3.4GHz equipment was not mentioned back in 2015 since it was not easily obtainable. 3.4 GHz may offer some great advantages. Nearly the same range of 2.4 and perhaps more quiet than the 5.8 band. Now that 3.4 gear is more available, albeit more expensive, and AREDN FW is available for a few radios, it may be ideal choice for long range backbone connections.