Broadband Noise vs DECT Phone

[#1]

In various reports about interference to ADSL, cordless (DECT) phones are often reported as potential causes of interference.
I have a problem that, by timing, appears to be caused by a new DECT phone, so I wondered how this kind of interference shows itself...
Does it appear when a DECT base-station is plugged into the phone line, but handsets are off?
Does it appear when handsets are turned on, but not engaged in a call?
Or does it only appear when a voice call is ongoing?
Any input/experience welcomed...
  Mike

[#2]

How close is the DECT base unit to your router? Advice seems to be to keep them physically well apart.
As an experiment have you got a second telephone socket or a doubler so that you could plug in a wired handset and listen on the line to see if you can hear anything (maybe a buzzing) when the DECT is used - you'd need to have the router disconnected while you did this.

[#3]

I had issues with a DECT phone a year or so back that dropped my line performance by around 30%. It wasn't just RF interference that caused an issue, it was sending nasty things back into the phone socket too.
I subsequently binned that phone, bought a Siemens device, moved the router to the other side of the room and connected it with a very nice shielded RJ11 cable and regained my line performance.
Paul

[#4]

Quote from: jelv

How close is the DECT base unit to your router? Advice seems to be to keep them physically well apart. As an experiment have you got a second telephone socket or a doubler so that you could plug in a wired handset and listen on the line to see if you can hear anything (maybe a buzzing) when the DECT is used - you'd need to have the router disconnected while you did this.

Router is plugged in to the master socket (with ADSLNation faceplate), while the DECT basestation (with one handset) is about 15 feet away, on an extension. A second handset is about 20 feet away.
I'll try the fixed-line phone idea, but it will be in a couple of weeks - this is all at my parents place...

[#5]

Quote from: youngsyp

I had issues with a DECT phone a year or so back that dropped my line performance by around 30%. It wasn't just RF interference that caused an issue, it was sending nasty things back into the phone socket too. I subsequently binned that phone, bought a Siemens device, moved the router to the other side of the room and connected it with a very nice shielded RJ11 cable and regained my line performance.

Thanks Paul - that seems in line with what I can see happening with my parent's modem.
I've attached a couple of graphs with what their line used to look like in August (when overnight noise could usually be better than daytime), and what it looks like now (where night-time is markedly worse).
If I trace through the logs, this night-time drop-off dates back to early September, on the day we bought a new DECT phone for my parents. It is sitting in the same location, plugged in to the same extension, but the behaviour is noticeable!
(OK - I can't attach 3 files. I'm trying with 2...)

[#6]

The third file...

[#7]

I have a set of three Panasonic Dects and no problem at all, one of the remote's sits next to the router, the main is about 10 foot from the router on a long phone cable

[#8]

I have a pair of Panasonic DECT phones (a few years old now). Originally, the DECT base station was in the living room, and the router upstairs in the study. No problems at all with that arrangement.
When I moved the base station upstairs near the router (plugged into the same socket via a single DSL filter), I began to suffer ADSL drops when the phone was in use (not just when it began to ring). The only thing that resolved it was by running a long extension from the DSL filter to the DECT phone and putting it on the other side of the room (keeping the router on a short lead). I don't know whether it was the physical distance of the base station, or the fact that the ultra-long extension to the phone attenuated any noise produced by it.
The DC adapters for the Panasonic DECT phones has been highlighted as a potential cause of problems. I have not found this to be the case with mine, which appear to use a transformer-based linear PSU and seem to output hardly any noise. The SMPS supplied with the BT Business Hub v2.0 (2wire 2700HGV) is absolutely dreadful though - it pretty much halves my sync rate from 2000kbps to 1000kbps when in close proximity to the BT extension outlet. If I put a MW radio near it, I get overpowering noise even 2 foot away. Cheap junk, strangely supplied with an above-average router.

[#9]

Some people have found that double filtering a DECT phone can help.
Edit: I should have said, I found this to be effective myself some years ago, but then the router/PC etc were moved to a different room and it wasn't needed.

[#10]

Thanks for the suggestions... I'll also check out the power supplies and the double-filtering idea.
The phones are BT Graphite models; I've not yet found anything online to show that they have a history of ADSL interference like the Panasonics did

[#11]

Just to complete this topic... I did some tests with my parent's phones & ADSL over Christmas, and can confirm...
- That the extra noise problems were caused by the new BT Graphite DECT handset being plugged in to the line.
- The power supplies didn't seem to have any particular effect on the line
- The best solution was to double-filter the DECT phone connection
The result is that the DECT phone is probably triple-filtered:
- The master socket has an ADSL-Nation filtered faceplate, to which the router is directly attached.
- An extension runs from the faceplate about 15 feet. Ring wire has previously been disconnected
- The extension socket then has 2 filters in series, then connected to the DECT phone.
Graphs attached to show the before-and-after effect...