I used the term FRS to indicate that unlicensed 2way radios are available in the 900 MHZ band. There are a variety of services that are also allocated for that band. The frequencies of interest for the radio modems are 902-904 and 926-928 MHz. The FCC allocation tables (www.fcc.gov) have fixed, mobile, broadcasting, radio location, amatuer radio and television, personal communications, ISM (?) and fixed microwave. Television stations also have a variety of products available in this band for point to point communications and data.
Without getting to techie (I can if you want!) the second harmonic of a 450 MHz radio can end up on frequency in the 900 MHz band very easily. But so can a variety of other things mixing together such as an FM transmitter mixing with a the second harmonic of a radio at 415 MHz. There can be mixing taking place right on your robot if you have loose metal in close proximity to the radio modem.
The bottom line here is most radio modem problems are easily solved by checking for bad cables, correct placement of the radio on the robot and keeping all teams from using radios in the pits. If you have done this in the past and think it's OK to operate with the modem in the pits, please stop, it's potentially dangerous for other teams in the pits and is bad for the competition.
Good Luck All