This module uses the core of Japan's CFJ455K filter elements , the center frequency of 455K, the bandwidth 1K, suitable for use in CW mode or SSB mode , the effect was particularly evident in CW mode , after opening the filter filters out most of the noise , only ticking sound, can significantly improve the recognition rate ; bandwidth voice SSB significantly narrowed down , the noise becomes small , but the sound is still recognizable , to hear what the other said , just sounds a little awkward , not 1K recommend using SSB bandwidth filter , consider using 2.7K bandwidth. The identification circuit with the filter can be inserted in the machine to identify what kind of filter, the filter may be generally of 1K 500,2.7 k displayed on the screen displayed on the screen of the filter 2.3 , so only the screen than to display FIL1 FIL2 intuitive , of course , you can also let display FIL1 FIL2 Colour:As Shown Material:plastic+metal Package Contents: 1x CW /SSB 2.7K narrowband filter Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.