For the best AM-SW Reception, the FI-30 filter is to be used when an AM antenna (0.1-26.5 MHz) is connected in tandem with a MK 20CA FM/TV antenna to the Naval Electronics AB Community Aerial System (CAS). The filter box is waterproof (IP56) and designed to be mounted close to the antenna in the masthead to conserve on the antenna cable installation. AM signals are coupled into the TV antenna (MK 20CA) down lead cable to the amplifier unit after it passes through the variable TV antenna attenuator AT20S that passes DC power and AM-SW without attenuation. Signals from the TV antenna lower than 30 MHz are blocked by the FI-30. TV signals above 40 MHz pass through the filter.
The AM input is protected against high static voltages by a built-in lightning arrestor. The FI-30 is supplied with a DC jumper feeding power to the active AM antenna ((VPA-30).). If a passive whip antenna is used, this jumper should be cut.