FAA in AC 90-50, allocates the related frequencies as follows:
- 121.950: Aviation Instructional and Support
- 122.750: Aircraft Air-to-Air
- 122.775: Aviation Instructional and Support
- 122.850: Special Use and Aviation Support on Non interference Basis
- 123.025: Helicopter Air-to-Air
- 123.300: Aviation Support
- 123.500: Aviation Support
Glider schools use 123.3 and 123.5 MHz,
balloons re-use the same frequencies for air-to-air and air-to-ground (chase vehicle) traffic.
Aircraft air-to-air frequency is 122.75 MHz.
It is confirmed this is the practice, e.g. for Greater Boston Soaring Club:
The frequencies of 123.3 and 123.5 MHz are assigned to flight schools
and glider operations. The soaring community uses 123.3 and 123.5 for
glider to glider as well as glider to ground communication. 123.5 is
used when 123.3 is too busy. 123.3 is also used as the "company"
frequency for various FBOs and flight operations.
FAA position for balloons
From FAA Balloon Flying Handbook:
There is confusion among pilots regarding frequencies that may be used
from air-to-ground, balloon-to-chase crew, for instance.
Many balloonists use 123.3 and 123.5 for air-to-ground (pilot-to-chase
crew), as these frequencies are for glider schools and not many
soaring planes are in the air at sunrise.
Since all users of the airwaves must have an ID or call, ground crews
may identify themselves by adding “chase” to the aircraft call sign.
For example, the chase call for “Balloon 3584 Golf” would be “3584
Golf Chase,” or perhaps simply “84 Golf Chase.”
The air-to-air frequency is 122.75. Remember that everyone in the air is using this frequency; transmissions should be kept brief. A
balloon pilot trying to contact a circling airplane would try 122.75
Legally, for air-to-air communications between private, fixed-wing
aircraft, there is just one authorized frequency: 122.75 MHz. For
general aviation helicopters: 123.025 MHz. Gliders and hot air
balloons share 123.3 and 123.5 MHz.