By April 27 all teams are required to send in their communications details (see rules section 2.c).  This should include frequencies being used, FCC license details (if applicable), and if you have the ability to select different channels with each frequency band.  Other information may be required for aerial vehicles (see rules section 1.b.ii), air breathing engines (see rules section 2.a.iii), or rovers over 75 kg (see rules section 2.b.ii).