The adaptive frequency control apparatus includes: a frequency
downstreamer for converting the frequency of the radio frequency signal
to a frequency of a defined band according to a reference signal; a
frequency error measurer for measuring a frequency error between a
frequency of the output signal of the frequency downstreamer and a
defined frequency; a loop filter for filtering the frequency error output
from the frequency error measurer based on a plurality of operational
parameters, the operational parameters being changeable; a differential
amplifier for generating a control signal for a voltage control based on
the output signal of the loop filter; and a voltage-controlled oscillator
for changing the frequency of the reference signal according to the
control signal of the differential amplifier.