According to Icom's description, the receiver's bandwidth is
More than 2.8 kHz/-6dB;
Less than 4.2 kHz/-60 dB
More than 15.0 kHz/-6dB;
Less than 30 kHz/-60 dB
More than 6.0 kHz/-6dB;
Less than 18 kHz/-60 dB
A CW signal has a bandwidth of about 200 Hz. Therefore, a narrower CW filter would significantly help the signal-to-noise ratio.
FL-132/FL-133 CW NARROW FILTERS
FL-132 is for the main band;
FL-133 is for the sub band operation.
Center frequency: 10.8491 MHz (FL-132);
10.9491 MHz (FL-133).
Passband width: 500 Hz/-6dB.
The instructions for installing the filter is in the instruction manual: