Radio ama­teurs are for­tu­nate to enjoy exclu­sive access to a few fre­quen­cy bands, mean­ing that they are not allo­cat­ed to any oth­er radio ser­vices. Oth­er bands are shared with one or more oth­er ser­vices on a co-pri­ma­ry basis. Access to some bands is on a sec­ondary basis, mean­ing that ama­teur sta­tions may not cause harm­ful inter­fer­ence to pri­ma­ry ser­vices and must accept any inter­fer­ence from them.

In the Table of Fre­quen­cy Allo­ca­tions a pri­ma­ry allo­ca­tion is shown in upper-case let­ters (AMATEUR) while a sec­ondary allo­ca­tion is shown in low­er case (Ama­teur). To under­stand the rel­a­tive sta­tus of ser­vices in shared bands it is also impor­tant to read the rel­e­vant foot­notes. A sum­ma­ry of the ama­teur spec­trum allo­ca­tions can be down­loaded here.

Defend­ing sec­ondary allo­ca­tions is a grow­ing chal­lenge, espe­cial­ly in the low microwave fre­quen­cies that are under severe pres­sure from com­mer­cial broad­band services.