The large insensitivity for coupling E-field noises into this antenna system is accomplished by : 

1. The amplifierasnd the splitter are installed in shielding closed metal boxes.
2. Three water resist N-busses are installed onto the amplifier, in good contact with the outside of the housing.
3. Three BNC-busses are installed onto the splitter box (Ant, RX and 12Vdc too), in good contact with the outside of the housing.
4. Mass surfaces of both PCBs are at one point grounded to the INSIDE their boxes.
6. Effective Common Mode Chokes (CMCs) are installed on the coax feeder every 3m..
7. The whole antenna system is grounded at ONE point : the receiver ONLY.

ALL these measures must be taken for optimal result.

    See "Construction details" and "De-noising the external powersupply"