. 2 5 ▁F SK ▁( Pack et ▁radio ) ▁and ▁PS K - 3 1 . ▁ ▁Mode ▁design ators ▁▁ ▁U pl ink ▁and ▁down link ▁design ations ▁use ▁sets ▁of ▁pa ired ▁letters ▁following ▁the ▁structure ▁X / Y ▁where ▁X ▁is ▁the ▁u pl ink ▁band ▁and ▁Y ▁is ▁the ▁down link ▁band . ▁Occ asion ally , ▁the ▁down link ▁letter ▁is ▁rendered ▁in ▁lower ▁case ▁( i . e ., ▁X / y ). ▁ ▁With ▁a ▁few ▁exceptions , ▁the ▁letters ▁correspond ▁to ▁IE EE ' s ▁standard ▁for ▁rad ar ▁frequency ▁letter ▁bands ... ▁ ▁{ | class =" wik itable " ▁| - ▁! Des ign ator ▁| H ▁| A ▁| V ▁| U ▁| L ▁| S ▁| S 2 ▁| C ▁| X ▁| K ▁| R ▁| - ▁! B and ▁| 1 5 ▁m ▁| 1 0 ▁m ▁| 2 ▁m ▁| 7 0 ▁cm ▁| 2 3 ▁cm ▁| 1 3 ▁cm ▁| 9 ▁cm ▁| 5 ▁cm ▁| 3 ▁cm ▁| 1 . 2 ▁cm ▁| 6 ▁mm ▁| - ▁! Fre quency ( General ) ▁| 2 1   M Hz ▁| 2 9   M Hz ▁| 1 4 5   M Hz ▁| 4 3 5   M Hz ▁| 1 . 2   G Hz ▁| 2 . 4   G Hz ▁| 3 . 4   G Hz ▁| 5   G Hz ▁| 1 0   G Hz ▁| 2 4