Choosing the proper ham band

900 MHz (M9)

• Penetrates trees and some obstacles
• Usually higher noise levels
• 6dB propagation advantage vs. 2.4 GHz for a given dish size
• Limited available spectrum – limit your channel bandwidth to 5 MHz (this will also improve the signal to noise ratio by 6dB).

2.4 GHz (M2)

• Only two non-overlapping 20MHz channels (1, 6) in Part 97
• Crowded and noisy band (ch 1+), interference from cordless phones, wireless routers and WIFI clients (part 15 and ISM unlicensed space)
• Channels -2 and -1 introduced in release 3.15.1.0 are uniquely under Part 97 and offer considerable improvement in Link Quality and distance given lack of unlicensed noise.  Care should be given in choosing bandwidth as ch -2 @ 20Mhz will push outside part 97. 

3.4Ghz (M3)

• 24 channels introduced in release 3.15.1.0 with no competing part 15 or ISM unlicensed users.
• Historically used by ATV groups to coordinate with.
• Least congested band.
• Caution to avoid primary Military usage for airborne and naval radar systems in costal areas and Military Operational Areas

5.8 GHz (M5)

• Relatively large amounts of spectrum available, so it is easier to co-locate other M5 devices
• Typically much quieter than 2.4 GHz, but as consumer devices transition to 5Ghz, is becoming as congested as 2.4Ghz
• 6dB propagation penalty vs. 2.4 GHz
• Channels 176 to 184 introduced in release 3.15.1.0 and are uniquely under Part 97 offering considerable improvement in Link Qualities and distance given lack of unlicensed noise.

General Rule: For a given gain, the higher the band, the smaller an antenna’s physical size needs to be. Therefore the propagation penalties of utilizing the higher bands are usually offset by the higher gain of similar sized antennas.