Man Made Noise Filtering

The most probable source of man made noise is coming from your own QTH. If you have not yet shut down all the equipment with the main AC switch do it first and listen with a battery powered rig. When you find an interfering equipment in your QTH the situation is good because you can replace the interfering equipment or add filter chokes to the cables.

Typically a switched mode power supply, inverter, charger, modem etc is conducting interference to cables and the cables are acting as an antenna and radiate RF noise. The biggest cable network is the mains network in your house which acts as a noise transmitting antenna. The worst bands are typically lower band 160 meter and 80 meter.

The RF interference is conducted to the cables which radiate the noise to your antenna

Unfortunately there are lot of power supplies and other equipment on the market which does not comply with the EMC standards.

An example test report of a non EMC compliant power supply which conducts much RF noise to mains network

The best option is to replace an interfering equipment but if it is not possible you can add filters chokes to the cables. The conducted noise is mainly common mode type ie. all the wires in the cables are radiating RF noise. Start with the longest cable, typically it is the mains input.

The conducted RF noise can be attenuated by adding filter chokes to the cables.

Mains filter choke (Yellow/Green is the protective GND). Toroidal ferrite core FT-240-31 with 8 or more turns.
8 turns provides common mode impedance of 1500 ohms on 160m, 2300 ohms on 80m and 2700 ohms on 40m.

DC filter choke with two wires. Toroidal ferrite core FT-240-31 with 11 turns.
It provides common mode impedance of 2700 ohms on 160m, 3800 ohms on 80m and 4600 ohms on 40m.

A DC filter choke and AC filters with plugs and sockets for mains filtering, all the ferrite cores are material 31.

Note. Take care of the electrical safety by keeping the mains filtrers in dry and safe palces.

See an e-bike charger man made noise case here

Update 2020-07-05 OH7SV

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