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It is to reduce voltage to the final curcuit, and then allows full voltage , its a cheap swing kit idea, The Connex really doesn't need it if tuned right, here's the tuning info::
VR1 "S" Meter Adjustment
VR4 Squelch Coarse Adjustment
VR5 FM Deviation Adjustment
VR8 RF Meter Adjustment
VR12 AM Low Power Modulation Limiter
VR13 High Power Adjustment
VR14 AM High Power Modulation Limiter
VR16 Low Power Adjustment
VR1 "S" Meter Adjustment
VR4 Squelch Coarse Adjustment
VR5 FM Deviation Adjustment
VR8 RF Meter Adjustment
VR12 AM Low Power Modulation Limiter
VR13 High Power Adjustment
VR14 AM High Power Modulation Limiter
VR16 Low Power Adjustment