Optimized for maximum sensitivity in the ham bands, the K3S or K3 can still be used for effective receiving of stations outside the ham bands. If, however, maximum sensitivity outside the ham bands is required, the KBPF3A will provide it.
Further, for any requirement to transmit outside the ham bands, the KBPF3A also supports MARS, Civil Air Patrol and many other groups who need this capability.
Lastly, used with the KSYN3A, the KBPF3A supports the new 630M band. This means that that the KBPF3A installed in a K3S will add an additional band to the K3S.
A: Yes, like many of the new K3S features, the KBPF3A can be installed in any K3 and in any order with other K3S Upgrade Kits.
A: Yes. The KBPF3A filters are required to achieve expected RF output on the MARS frequencies.
A: Yes. You can still listen to them without the KBPF3A installed but reception will not be optimal. Maximum sensitivity for DXing in the SWL bands is achieved with the KBPF3A installed.