Filter for power supply, for ADSL router

Thread Starter


Joined Jul 2, 2008
I have new 12V, 5A switching power supply, I connected it to my LED light when the electriccity is on,

I connected it to my ADSL router 12v, my internet quality gone down with SNR lowered, it is noise come from that PS, but when I supplied it (the router) with other DC sources, it come to work fine, so

I decided to add a filter before DC input of that router, I think I need the same filter of ADSL/Phone?
What I want to make it my self, because I don't trust that filters (weak to supply my router), but all filters that have don't have part number of coil
(I want to add 100uF cap too)

Filters here have one capacitor 10nF (103) and one unknown coil.
Now my question:
1- What the number in uH that coil, I am guessing from reading on internet it is 10uH, and some said 6.uH
2- How can I make it my self from toroid inducor that come inside "saving florescent lamp" circuits

Any idea to make that DC inuput filtered without any noise for my router?

I don't have oscillator or LC meter

Thanks in advance
Last edited:
Your idea of a filter is somewhat odd because the modem gets the full frequency spectrum. i.e 0-1Mhz or whatever,
The phones see DC to about 4 kHz.

Use a splitter in the NID instead. You only need one for the entire house.