Buzz on the line!

For months we have had a buzz on our DECT telephone. We don't use the
landline much, or at least I don't - most of my calls are via mobile.
This evening I decided to investigate the noise....

I pulled the modem out of the filter, buzz still there. Tried moving
the DECT base unit away from the wireless modem. Tried a spare DECT
phone + base unit in the filter, then finally a wired phone in the
filter. Nothing fixed the buzz, until I accidently nudged the filter to
one side and the noise instantly disappeared.

Modem, DECT base, LAN print-server and a few other bits are fed via one
of those multiway 13amp outlets, with surge protection and protection
for the telephone line. The DSL filter has a short 4" lead on it to
plug into the above unit. Having such a short lead, the filter was
resting on top of the wallwart unit for the DECT base unit. Once the
filter was moved away from the wallwart the buzz disappeared. Obviously
the wallwart had a transformer in it and the mains hum was being picked
up by the filter lying on top of it.

The moral being - never put your DSL filters anywhere near a
transformer, no matter how small the transformer

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk




Harry Bloomfield

Harry Bloomfield wrote:

> Once the filter was moved away from the wallwart the buzz disappeared.
> Obviously
> the wallwart had a transformer in it and the mains hum was being picked
> up by the filter lying on top of it.

It's called electromagnetic induction and was discovered by Faraday in 1831.
http://en.wikipedia.org/wiki/Electromagnetic_induction

My advice is never to put *ANY* electronic device or equipment near 'wall warts'
or other external power supplies/chargers. They're EXTERNAL for a reason.

Graham

On Sat, 1 Sep 2007 03:13:31 UTC, Eeyore
<(E-Mail Removed)> wrote:

> Harry Bloomfield wrote:
>
> > Once the filter was moved away from the wallwart the buzz disappeared.
> > Obviously
> > the wallwart had a transformer in it and the mains hum was being picked
> > up by the filter lying on top of it.
>
> It's called electromagnetic induction and was discovered by Faraday in 1831.
> http://en.wikipedia.org/wiki/Electromagnetic_induction
>
> My advice is never to put *ANY* electronic device or equipment near 'wall warts'
> or other external power supplies/chargers. They're EXTERNAL for a reason.

One major reason is not technical at all. It's to cut down on safety
approval times. If a unit works only on low voltage, it doesn't need
safety apprival itself (well, not in the same rigorous way). So a
manufacturer will then buy in a pre-approved wall wart for each country.

--
[ 7'ism - a condition by which the sufferer experiences an inability
to give concise answers, express reasoned argument or opinion.
Usually accompanied by silly noises and gestures - incurable, early
euthanasia recommended. ]

"Harry Bloomfield" <(E-Mail Removed)> wrote
in message news:(E-Mail Removed)

[snip]

: : Modem, DECT base, LAN print-server and a few other bits
: : are fed via one of those multiway 13amp outlets, with
: : surge protection and protection for the telephone line.
: : The DSL filter has a short 4" lead on it to plug into
: : the above unit. Having such a short lead, the filter
: : was resting on top of the wallwart unit for the DECT
: : base unit. Once the filter was moved away from the
: : wallwart the buzz disappeared. Obviously the wallwart
: : had a transformer in it and the mains hum was being
: : picked up by the filter lying on top of it.

Wallwart..?

Ivor

"Ivor Jones" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> "Harry Bloomfield" <(E-Mail Removed)> wrote
> in message news:(E-Mail Removed)

> : : Obviously the wallwart
> : : had a transformer in it and the mains hum was being
> : : picked up by the filter lying on top of it.
> Wallwart..?

Transformer+PSU built into a mains plug, with a low-voltage lead to the
appliance that it's powering.

On Sat, 1 Sep 2007 10:42:03 UTC, "Mortimer" <(E-Mail Removed)> wrote:

> "Ivor Jones" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
> > "Harry Bloomfield" <(E-Mail Removed)> wrote
> > in message news:(E-Mail Removed)
>
> > : : Obviously the wallwart
> > : : had a transformer in it and the mains hum was being
> > : : picked up by the filter lying on top of it.
> > Wallwart..?
>
> Transformer+PSU built into a mains plug, with a low-voltage lead to the
> appliance that it's powering.

And sometimes *just* a transformer. I repaired one recently that was
like that.

--
[ 7'ism - a condition by which the sufferer experiences an inability
to give concise answers, express reasoned argument or opinion.
Usually accompanied by silly noises and gestures - incurable, early
euthanasia recommended. ]

"Mortimer" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)
: : "Ivor Jones" <(E-Mail Removed)> wrote in message
: : news:(E-Mail Removed)...
: : : "Harry Bloomfield" <(E-Mail Removed)>
: : : wrote in message
: : : news:(E-Mail Removed)
: :
: : : : : Obviously the wallwart
: : : : : had a transformer in it and the mains hum was
: : : : : being picked up by the filter lying on top of it.
: : : Wallwart..?
: :
: : Transformer+PSU built into a mains plug, with a
: : low-voltage lead to the appliance that it's powering.

Strange definition, never heard it before.

I've always just called them plug-top PSU's.

Ivor

On Sat, 1 Sep 2007 13:35:38 +0100, Ivor Jones wrote:

>:: Transformer+PSU built into a mains plug, with a
>:: low-voltage lead to the appliance that it's powering.
>
> Strange definition, never heard it before.
>
> I've always just called them plug-top PSU's.

Warning: excessive number of grocers' apostrophes in this thread!
--
Peter.
You don't understand Newton's Third Law of Motion?
It's not rocket science, you know.

"PeterC" <(E-Mail Removed)> wrote in message
news:147ynzojbq1r4$.f66de7jl8p2d$.(E-Mail Removed)
: : On Sat, 1 Sep 2007 13:35:38 +0100, Ivor Jones wrote:
: :
: : : : : Transformer+PSU built into a mains plug, with a
: : : : : low-voltage lead to the appliance that it's
: : : : : powering.
: : :
: : : Strange definition, never heard it before.
: : :
: : : I've always just called them plug-top PSU's.
: :
: : Warning: excessive number of grocers' apostrophes in
: : this thread!

Oops..! Only one was mine though..!

Ivor

On Sat, 1 Sep 2007 21:30:47 UTC, PeterC <(E-Mail Removed)>
wrote:

> On Sat, 1 Sep 2007 13:35:38 +0100, Ivor Jones wrote:
>
> >:: Transformer+PSU built into a mains plug, with a
> >:: low-voltage lead to the appliance that it's powering.
> >
> > Strange definition, never heard it before.
> >
> > I've always just called them plug-top PSU's.
>
> Warning: excessive number of grocers' apostrophes in this thread!

Thats [1] Ivor for you.

[1] Trying to redress the balance...
--
[ 7'ism - a condition by which the sufferer experiences an inability
to give concise answers, express reasoned argument or opinion.
Usually accompanied by silly noises and gestures - incurable, early
euthanasia recommended. ]