▁the ▁overall ▁capac it ance ▁and ▁the ▁capac it ance ▁range ▁by ▁half , ▁but ▁has ▁the ▁advantage ▁of ▁reducing ▁the ▁AC ▁component ▁of ▁voltage ▁across ▁each ▁device ▁and ▁has ▁symmet rical ▁dist ort ion ▁should ▁the ▁AC ▁component ▁possess ▁enough ▁amplitude ▁to ▁bias ▁the ▁var ic aps ▁into ▁forward ▁condu ction . ▁ ▁When ▁design ing ▁tun ing ▁circ uits ▁with ▁var ic aps ▁it ▁is ▁usually ▁good ▁practice ▁to ▁maintain ▁the ▁AC ▁component ▁of ▁voltage ▁across ▁the ▁var ic ap ▁at ▁a ▁minimal ▁level , ▁usually ▁less ▁than ▁ 1 0 0   m V ▁peak ▁to ▁peak , ▁to ▁prevent ▁changing ▁the ▁di ode ▁capac it ance ▁too ▁much , ▁which ▁would ▁dist ort ▁the ▁signal ▁and ▁add ▁harm on ics . ▁ ▁A ▁third ▁circuit , ▁at ▁top ▁right ▁in ▁diagram , ▁uses ▁two ▁series - connected ▁var ic aps ▁and ▁separate ▁DC ▁and ▁AC ▁signal ▁ground ▁connections . ▁The ▁DC ▁ground ▁is ▁shown ▁as ▁a ▁traditional ▁ground ▁symbol , ▁and ▁the ▁AC ▁ground ▁as ▁an ▁open ▁triangle . ▁Se par ation ▁of ▁grounds ▁is ▁often ▁done ▁to ▁( i ) ▁prevent ▁high - fre quency ▁radiation ▁from ▁the ▁low - fre quency ▁ground ▁node , ▁and ▁( ii ) ▁prevent ▁DC ▁curr ents ▁in ▁the ▁AC ▁ground ▁node ▁changing ▁bias ▁and ▁operating ▁points ▁of ▁active ▁devices ▁such ▁as ▁var ic aps ▁and ▁trans ist ors . ▁ ▁These ▁circuit ▁configurations ▁are ▁quite ▁common ▁in ▁television ▁tun ers ▁and ▁electron ically ▁tun ed ▁broadcast ▁AM ▁and ▁FM ▁rece ivers