Airprobe xlating filter question

It’s known that the channel band width is 200KHz

When looking into airprobe, gsm_receiver.py

the cutoff freq in xlating is 145KHz, Can anyone kindly to explain.
Thanks!

filter_cutoff = 145e3
filter_t_width = 10e3

filter_taps = gr.firdes.low_pass(1.0, self.input_rate,
filter_cutoff,
filter_t_width, gr.firdes.WIN_HAMMING)

filtr = gr.freq_xlating_fir_filter_ccf(1, filter_taps, offset,
self.input_rate)

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