[clug] OT: ADSL2+ and AM radio interference

Owen rcook at pcug.org.au
Sun Apr 25 21:12:24 MDT 2010

On Mon, 26 Apr 2010 00:53:00 +1000
Adam Baxter <voltagex at voltagex.org> wrote:

> Can anyone on this list confirm or deny some of the things said on
> this post:
> http://forums.whirlpool.net.au/forum-replies-archive.cfm/369495.html
> "Interference from AM radio transmitters is a known cause of noise
> induction into the copper network."

Many reports in ye olden days of people being able to hear the radio
through their telephone (land line). Even an electric stove hit the
news as a radio receiver!

Basically, wiring will act as an antenna. If you have a device
connected to a bit of wire, and you get radio interference, the fault
is with your equipment not being designed for its intended purpose.

The reality is that saving cents in manufacture is all that matters,
so input filtering is one of those things that goes and the user has
to make other arrangements to get rid of the interference.  

> *  I've been getting quite a bit of radio interference when listening
> to ABC on AM. Coincidentally my ADSL sync speed and reliability has
> been degrading steadily. Are these related?
> * Are noisy AC-DC adapters to blame? If so, how can I isolate which
> one without unplugging my whole house?
> * Is there a way (other than ye-olde AM receiver) to measure
> where/what the noise is?

Determining noise sources can be a bit of a black art. Once upon a time
if you got a crackle in your radio, you could ring the District Radio
Inspector who generally would find the source of the noise for you.
However, 20 plus years ago, a fee was imposed for this service, and
magically overnight, all interference ceased.  The flow on effect of
this was that no one became trained in the black art of noise source

However, in your case, ye-olde AM receiver is the way to go. You have
to detect rf energy, you can only do this with a detector!

Just wander round the house till the noise gets louder! Welders can be
a problem because they can be several houses/blocks away (neighbours
think you are ready for the looney bin when they see you wandering
down the road waving a radio about). Dimmers, faulty switches and faulty
equipment can all add to the noise.

Do you have any back to base alarms connected to the line? 

> * Would strategically placed ferrite "lifesavers" help or is it
> snake-oil?

Yes, they should been built into the equipment in the first place. But
if you as you already have filters on your line, it is probably
best to know what you are trying to block before adding yet another

> * Is there any way to shield the modem itself? (
> http://forums.whirlpool.net.au/forum-replies.cfm?t=369495&r=5426693#r5426693
> )


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