▁and ▁begins ▁to ▁move ▁away , ▁this ▁process ▁is ▁revers ed . ▁ ▁The ▁down link ▁frequency ▁will ▁appear ▁lower ▁and ▁the ▁u pl ink ▁frequency ▁will ▁need ▁to ▁be ▁adjust ed ▁higher . ▁ ▁The ▁following ▁mathematical ▁formulas ▁relate ▁the ▁Do pp ler ▁shift ▁to ▁the ▁velocity ▁of ▁the ▁satellite . ▁ ▁Due ▁to ▁the ▁complexity ▁of ▁finding ▁the ▁relative ▁velocity ▁of ▁the ▁satellite ▁and ▁the ▁speed ▁with ▁which ▁these ▁corre ctions ▁must ▁be ▁made , ▁these ▁calculations ▁are ▁normally ▁accomplished ▁using ▁satellite ▁tracking ▁software . ▁ ▁Many ▁modern ▁trans ce ivers ▁include ▁a ▁computer ▁interface ▁that ▁allows ▁for ▁automatic ▁do pp ler ▁effect ▁correction . ▁ ▁Man ual ▁frequency - shift ▁correction ▁is ▁possible , ▁but ▁it ▁is ▁difficult ▁to ▁remain ▁precisely ▁near ▁the ▁frequency . ▁ ▁Fre quency ▁mod ulation ▁is ▁more ▁toler ant ▁of ▁do pp ler ▁sh ifts ▁than ▁single - side band , ▁and ▁therefore ▁FM ▁is ▁much ▁easier ▁to ▁t une ▁manually . ▁ ▁FM ▁sat ell ites ▁▁ ▁A ▁number ▁of ▁low ▁earth ▁orbit ▁( LE O ) ▁OS C AR ▁sat ell ites ▁use ▁frequency ▁mod ulation ▁( FM ). ▁ ▁These ▁are ▁also ▁commonly ▁referred ▁to ▁as ▁" FM ▁LE Os " ▁or ▁the ▁" FM ▁Bird s ". ▁ ▁Such ▁sat ell ites ▁act ▁as ▁FM ▁amateur ▁radio ▁repe aters ▁that ▁can ▁be ▁communic ated ▁through ▁using ▁commonly ▁available ▁amateur ▁radio ▁equipment . ▁ ▁Communic ation ▁can ▁be ▁achieved ▁with ▁hand h eld ▁trans ce ivers ▁using ▁manual ▁do pp ler ▁correction