  G Hz ▁| 4 7   G Hz ▁| - ▁| } ▁ ▁Prior ▁to ▁the ▁launch ▁of ▁OS C AR ▁ 4 0 , ▁operating ▁modes ▁were ▁designated ▁using ▁single ▁letters ▁to ▁indicate ▁both ▁u pl ink ▁and ▁down link ▁bands . ▁ ▁While ▁deprecated , ▁these ▁older ▁mode ▁design ations ▁are ▁still ▁widely ▁used ▁in ▁cas ual ▁conversation . ▁ ▁Mode ▁A : ▁ 2 ▁m ▁u pl ink ▁/ ▁ 1 0 ▁m ▁down link ▁Mode ▁B : ▁ 7 0 ▁cm ▁u pl ink ▁/ ▁ 2 ▁m ▁down link ▁Mode ▁J : ▁ 2 ▁m ▁u pl ink ▁/ ▁ 7 0 ▁cm ▁down link ▁ ▁Do pp ler ▁shift ▁ ▁Due ▁to ▁the ▁high ▁orb ital ▁speed ▁of ▁the ▁amateur ▁sat ell ites , ▁the ▁u pl ink ▁and ▁down link ▁frequencies ▁will ▁vary ▁during ▁the ▁course ▁of ▁a ▁satellite ▁pass . ▁ ▁This ▁phenomen on ▁is ▁known ▁as ▁the ▁Do pp ler ▁effect . ▁ ▁While ▁the ▁satellite ▁is ▁moving ▁towards ▁the ▁ground ▁station , ▁the ▁down link ▁frequency ▁will ▁appear ▁to ▁be ▁higher ▁than ▁normal . ▁Hence , ▁the ▁receiver ▁frequency ▁at ▁the ▁ground ▁station ▁must ▁be ▁adjust ed ▁higher ▁to ▁continue ▁receiving ▁the ▁satellite . ▁ ▁The ▁satellite ▁in ▁turn , ▁will ▁be ▁receiving ▁the ▁u pl ink ▁signal ▁at ▁a ▁higher ▁frequency ▁than ▁normal ▁so ▁the ▁ground ▁station ' s ▁transm itted ▁u pl ink ▁frequency ▁must ▁be ▁lower ▁to ▁be ▁received ▁by ▁the ▁satellite . ▁ ▁After ▁the ▁satellite ▁passes ▁overhead