| 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 to your antenna. The biggest cable network
is the mains network in your house which acts as a noise transmitting
antenna. The worst bands are typically lower bands 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 end.
The conducted RF noise can be attenuated by adding choke filters to the cables.
Mains filter choke (Yellow/Green is the protective
GND). Toroidal ferrite core FT-240-31 (Fair-Rite 2631803802) 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 (Fair-Rite 2631803802) 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.A good option is to use a big snap-on ferrite material 31 Fair-Rite 0431177081. It provides 1000 ohm with only 3 turns on 80 meters Corresponding Fair-Rite fixed ferrite tube 2631626202 provides even higher impedance. 4 turns provides 1500 ohms and 5 turns privides even 2500 ohm on 160m. 
Mains filter choke on Fair-Rite 0431177081 made by M0PZT Fair-Rite 2631626202 with 2x7 turns >4000 ohms Note. Take care of the electrical safety by keeping the mains filters in dry and safe palce. See an e-bike charger man made noise case here Update 2022-09-09 OH7SV Back to OH7SV ham projects |
