narrow telegraph filter (500 Hz at -6 dB level) Icom FL-100. Suitable for devices such as Icom IC-721 - IC-729, as well as: IC-575, IC-706, IC-703, IC-738, IC-746, IC-756, IC-760, IC-775, IC- 780, IC-78, IC-M700PRO, IC-M710, IC-R72, IC-R75 and possibly some more.