High attenuation low pass / band pass filters
Marine MF/HF signals are often transmitted with high power and have the potential to interfere with other receiving radios as an out-of-band signal. If this is a concern, every other antenna should have a suitable filter blocking the interfering bands.
If there is a concern that the MF/HF radio will transmit harmonical frequencies, a low-pass filter should be installed between each transmitting radio and their antenna. This way we prevent the harmonic out-of-band signals from leaking out from the antenna.
If we cannot rely on the selectivity of the radios themselves to not get saturated by strong interfering signals originating from in-band transmissions, static band-pass filters should be deployed.
Band-pass filters can also be used when one wants to attenuate spurious frequencies below the transmitted frequencies from leaking out.
The utilization of low-pass, band-pass and even duplex/diplex filters helps preventing the transmission of unwanted spurious or harmonic signals typically generated inside transmitter itself.
Other benefits are significantly reduced electromagnetic signature, reduced risk for front-end overload of nearby receiver and a reduced risk for passive inter modulation of radios.
