Bob Urz wrote:

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?

Any ideas or links?


Make a tuned trap for the station's carrier frequency, and put it
across the phone line. You can use the antenna coil and variable
capacitor from a junk am radio, or buy the parts from Mouser or one of
the places selling parts for crystal radios. Connect the antenna coil
and variable capacitor in series, then connect the filter across the
line. Tune it for minimum RF on the line. (Scope or AC coupled AC
voltmeter)

If you have a lot of outlets on that phone line you may need more
than one filter. The cheap "electronic network" used in cheap, modern
phones can rectify the RF and give you fits. The old transformer and
capacitors didn't cause these problems.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida