AM radio interference on voice when DSL is on

[Martin Pergler]

I just bought a voice speakerphone/answering system combo and it
doesn't get along with my DSL connection in a weird way.

I can make incoming calls and outgoing calls on the phone, and the DSL
connection and speed are fine. However:

1. When I'm using the speakerphone for more than 10 minutes or so, I
start hearing a radio station in the background

2. When the answering system picks up an incoming call, it records
only the 1st 3 seconds and then terminates, as if it did not recognize
the call was active

If I turn off the DSL modem, the answering system behaves normally and
I hear no AM radio.

I do have an inline DSL filter connected in series with the
speakerphone. Before I bought the speakerphone, I used a cheapo phone
on which I found I needed to put 2 DSL inline filters in series to
make modem buzz go away, which was a bit perplexing but did not seem
significant. Now I'm starting to think it may have been. The telco,
dsl provider, and speakerphone technical support are having a grand
old time expressing surprise and blithely blaming each other.

I've googled and read a couple of hints on this newsgroup, but they
seem to talk about 2 slightly different things: AM interference with
the DSL connection itself (not my case), or RFI interference on a
phone line from nearby AM stations (which ought to be independent of
whether my DSL modem is on or not). I also found something about lines
being "unbalanced", butI'm not sure what that means -- though I may
become unbalanced myself if I can't figure this out. I do also have a
fax connected (unplugging it does not help), and the behaviour is the
same if I try a different phone jack. I'm in an old apartment where
someone ought to simplify the wiring, but I'd much rather it didn't
have to be me.

Any suggestions...

Thanks, Martin

[Rick Wintjen]

Post by Martin Pergler
I just bought a voice speakerphone/answering system combo and it
doesn't get along with my DSL connection in a weird way.
I can make incoming calls and outgoing calls on the phone, and the DSL
1. When I'm using the speakerphone for more than 10 minutes or so, I
start hearing a radio station in the background
2. When the answering system picks up an incoming call, it records
only the 1st 3 seconds and then terminates, as if it did not recognize
the call was active
If I turn off the DSL modem, the answering system behaves normally and
I hear no AM radio.
I do have an inline DSL filter connected in series with the
speakerphone. Before I bought the speakerphone, I used a cheapo phone
on which I found I needed to put 2 DSL inline filters in series to
make modem buzz go away, which was a bit perplexing but did not seem
significant. Now I'm starting to think it may have been. The telco,
dsl provider, and speakerphone technical support are having a grand
old time expressing surprise and blithely blaming each other.
I've googled and read a couple of hints on this newsgroup, but they
seem to talk about 2 slightly different things: AM interference with
the DSL connection itself (not my case), or RFI interference on a
phone line from nearby AM stations (which ought to be independent of
whether my DSL modem is on or not). I also found something about lines
being "unbalanced", butI'm not sure what that means -- though I may
become unbalanced myself if I can't figure this out. I do also have a
fax connected (unplugging it does not help), and the behaviour is the
same if I try a different phone jack. I'm in an old apartment where
someone ought to simplify the wiring, but I'd much rather it didn't
have to be me.
Any suggestions...
Thanks, Martin

Start by going to Radio Shack and getting one of their telephone line
polarity testers. Looks kind of like a AAA battery with a short piece of
line and connector on one end, a LED on the other. Test all lines. If
polarity is good (green light), try a better filter (or cascade them, as
before). It could be the DSL signalling is reducing the noise immunity
of the electronic front end of the phone, allowing the radio signal to
more easily penterate via intermodulation effects.
Also, is your DSL modem on a 'home run' line, or is it on a daisy chain
linking all jacks in a series, starting at the NID? A home run might
reduce the problem.