Joerg wrote:

Hello Bob,

Anybody got a good resource on how to build a phone line filter?
I am near a AM radio tower and its really killing my dial up modem
at times. I tried a DSL filter in line. but i think the AM band is
not getting attenuated enough to do much good.

Its hard to peg characteristics. Would a modem be considered a 200 ohm
nominal load on the phone line?

What type of filter for AM radio?

Dual inline inductors?
parallel capacitor with series resistor maybe?


If a series connection of DSL blockers doesn't work you might want to
try a common mode choke. Either one off the shelf or take a #77 core and
wind twisted pair through it as many times as it'll comfortably fit
through there. In a pinch the core of a discarded flyback transformer or
the big ferrite from a scrapped AT power supply can do. Mains
transformer cores would not be so good here.

I have here a BT RF2 filter.

It simply consists of a 2.2mH choke in both lines.

Like these
http://uk.farnell.com/jsp/endecaSear...jsp?SKU=432167

I'll post a pic in abse.

I'd expect a common mode choke to be better of course.

Graham