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Can DECT Phones interfere with Broadband?

VileReynard
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Can DECT Phones interfere with Broadband?

Although I have a wireless router I am not aware of any Wireless interference.
However, whilst running routerstats (which uses a wireless connection to telnet to the router every 60 seconds),
I noticed that my noise margin fell from 6dB to 3dB (without any change in sync speed) when a telephone call was made.
It recovers as soon as the phone is returned to the base station.
This  effect is quite reproducible.
The router and DECT share a power strip and plug into the two halves of the same filter (different filters have been tried).

Is it possible that a DECT (2.4GHz) can interfere with ADSL (2MHz)?

The two devices are about two feet apart (vertically) and no other re-location is physically possible.

18 REPLIES
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Re: Can DECT Phones interfere with Broadband?

I saw the same effect only worse and it happened with an ordinary phone as well.
It seemed to be the ringing which did the damage so I tried it by phoning in from my mobile while the phone was disconnected and it still happened.
In my case it took a long time to more or less sort it including replacing the line card at the exchange
If it is only with the DECT phone you could try double filtering the phone - for some reason it seemed to help in my case
VileReynard
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Re: Can DECT Phones interfere with Broadband?

Thanks!
I'll do that as soon as the "better half" gets off the phone Smiley
I'll report back ASAP - which could be hours Crazy

pierre_pierre
Grafter
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Registered: 30-07-2007

Re: Can DECT Phones interfere with Broadband?

I am not convinced that it is Dect phone,  I have the main unit about 3 inches from the router and two extensions, three phones in all, one is about two feet from this mobile I also have two other none Wifi phones for use during power cuts, all phones have a single filter.  I am on a thirty plus old system with no master socket, Synch 8125 profile 7150
VileReynard
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Re: Can DECT Phones interfere with Broadband?

I'm convinced!
See the pretty graphs below:-
http://dl.getdropbox.com/u/449229/NoiseMargin-2009Feb14-1504.jpg
and
http://dl.getdropbox.com/u/449229/NoiseMargin-2009Feb14-1720.jpg
Unfortunately that sudden plummet at the end of the second graph was a test carried out by me,
just after double filtering the DECT (but only single filtering the ADSL).
Since noise margin is around 5.5 - 6.5dB in the absence of phone calls, I'd put forward a clear
case for DECT interference, Cry
BTW This is in new D-Link router.

Community Veteran
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Re: Can DECT Phones interfere with Broadband?

No drop when the phone wasn't connected but you phoned in then
pierre_pierre
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Registered: 30-07-2007

Re: Can DECT Phones interfere with Broadband?

well I just tested mine, mobile to home phone in the same room, router stats didnt move, but my snr is always 11-12  I for one am happy
VileReynard
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Re: Can DECT Phones interfere with Broadband?

Quote from: Oldjim
No drop when the phone wasn't connected but you phoned in then

The phone was connected at all times (with the exception of the time it took to stick in an extra filter).
Those periods when the noise margin was below about 5dB were when the phone was lifted out
of it's cradle and in use.
I've had a thought - when the phone is "active" and generating it's 2.4GHz RF - could these interact
with the nearby wireless router and generate harmonics in the 2MHz ADSL region?
Can't say I know much about these things - but it seems a possibility according to
http://en.wikipedia.org/wiki/Hetrodyne#Mathematical_principle

itsme
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Re: Can DECT Phones interfere with Broadband?

Quote from: The
I'm convinced!
-----
Since noise margin is around 5.5 - 6.5dB in the absence of phone calls, I'd put forward a clear
case for DECT interference, Cry

You can only come to this conclusion if you do identical tests with a POTS. I have used both DECT and POTS and both increase my SNRM from 12db to 15db. So my conclusion is that DECT phones do not affect the line.
itsme
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Re: Can DECT Phones interfere with Broadband?

Quote from: The
---
I've had a thought - when the phone is "active" and generating it's 2.4GHz RF - could these interact
with the nearby wireless router and generate harmonics in the 2MHz ADSL region?

DECT phones are transmitting on their carry frequency all the time irrespective whether the phone is being used or not.
VileReynard
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Re: Can DECT Phones interfere with Broadband?

I didn't mention this before but I've got an old (pulse-dial) corded phone connected in with the DECT.
I'm using a simple double coupler.
Here are the results:-
(The DECT was in action in the early part of this graph) - and finally fell to zero, which has knocked my speed back a bit Cry Cry
The DECT was hung up fairly swiftly and my noise margin shot up to 8+dB
The fall from 8.3dB to about 6dB was caused by the POTS corded phone.
Subsequent climb back to 7.5 dB was with all phones back on-hook.
Why is this happening - I haven't changed my phone for many years. Lips are sealed Lips are sealed
http://dl.getdropbox.com/u/449229/NoiseMargin-2009Feb14-1915.jpg

itsme
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Re: Can DECT Phones interfere with Broadband?

The question to ask is how does the router/modem calculate the SNRM? When it went to 0 did you lose sync?
VileReynard
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Re: Can DECT Phones interfere with Broadband?

I didn't obviously loose contact when the SNRM hit zero, but since the
router sync speed dropped from 5766Kbps to 5407Kbps then I must have Smiley
I have detailed stats from the log file:-
Quote
Sat 14 Feb 2009  18:49:32,    Noise Margin= 5.9, Sync Speed= 5766
Sat 14 Feb 2009  18:50:32,    Noise Margin= , Sync Speed=
Sat 14 Feb 2009  18:52:22,    Noise Margin= 6.7, Sync Speed= 5407

I haven't revealed these until now - I've got lots!

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Re: Can DECT Phones interfere with Broadband?

Perhaps your first filter has gone faulty, if it's been driving an old dial telephone with a bell? if it's a 1000 ohm bell and not 4000 ohm more than likely.
VileReynard
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Re: Can DECT Phones interfere with Broadband?

That is old data Smiley
Since then I have fitted an i-plate (which prevents interference from any source using the bell wire as an aerial and feeding it into my ADSL signal).
I have used routerstatslite to monitor noise margin with a resolution of 0.1dB
Using a DECT or a wired phone is undetectable within the medium term natural variation of +/- 0.2dB of noise.
So - DECT doesn't now affect my signal (if it ever did)  - although it can do for some people.