[Telecom] Does ADSL interfere with cordless phone?

I posted this in the XDSL group, but that group is too quiet.

Recently, I had a new phone service installed, shared with ADSL. I used the filters shipped with the DSL device, but I'm getting lousy sound on my old cordless phone, Sony SPP 2000, a 1.7 Mhz instrument. Yes, I know that such phones were always inadequate and readily overheard, but the handset is cool looking, it has swappable sealed lead acid batteries which means the handset is never recharged in the base. It's survived being dropped quite a lot.

Anyway, do these require a different filter than the one that came in the box?

Reply to
Adam H. Kerman
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I had a problems like that, AT&T placed a filter at the Network outside the house and ran a new cable direct to the DSL, that took care of the problem as the voice phones no longer needed the filter.

Reply to
Steven

Was the filter on everything, on the branch going to the DSL device, or ahead of the branches going to the phone jacks?

Reply to
Adam H. Kerman

The Tech removed all the filters from my phones and placed a DSL interface above the network interface, ran a pair to the DSL and used another pair to the DSL, in other words the DSL jack is it own and the regular phones that run through the house are also on a pair. The voice is on the blue pair, DSL is on orange pair and the second line is on the green pair

Reply to
Steven

In my experience, it's best to leave the DSL filter off at the cordless base station. Cordless phones are already bandwidth limited and highly filtered to remove the artifacts from their own RF stages.

--Gene

***** Moderator's Note *****

Gene, I think the filters are mostly to benefit the ADSL modem, which needs all the signal strength it can get: some phones short out the high frequencies the ADSL gear is tryin to hear.

Bill Horne Moderator

Reply to
Gene S. Berkowitz

ADSL performance is based on maximum possible S/N ratio at the remote modem end: allow another digital device to pump even tiny amounts of HF noise into the line (which "normal" handsets care little about) and you will find you maximum sync rate far lower than it could be.

Just don't use one filter on a cordless base station, use two.

Reply to
David Clayton

The standard DSL filters (line in, phone out) are not going to achieve that result; these are not isolators, they're impedance matching low-pass filters. What is called for is a DSL splitter (line in, phone out + modem out).

That's just silly.

--Gene

Reply to
Gene S. Berkowitz

Most ADSL filters are designed to be low pass in one direction but they do seem to also have low pass characteristics in the other direction (these things are invariably built to the lowest cost to do the basic job - which does not include filtering in the opposite direction).

The purpose of putting two on a digital handset base station which has the potential to put the internally generated digital hash back into the phone line it connects to - which is very bad for any ADSL signal that is also on that line - is to reduce that potential hash.

Using two "standard" ADSL line filters with some filtering in the other direction will be better than using just one - and a nice simple solution for people who may not have the knowledge to source better quality filters that will do the job better.

Reply to
David Clayton

No, most filters are not directional at all, only the packaging is (jack on one end, plug on the other, but in performance it makes no difference).

I don't think that this is true of any cordless base station made in the last 10 years. Compliance with EMC guidelines (EN55024) makes internal filtering on the incoming cable practically mandatory to avoid conducted interference.

--Gene

Reply to
Gene S. Berkowitz

The cordless phone in question is older.

It doesn't look like [there is] a consensus of opinion as to what I should do...

***** Moderator's Note *****

I suggest doing some binary tests:

  1. Measure your DSL upload and download speed as it is now. Do the test at 4 AM so there's a minimum of variance in the speed readings from one test to another. There's a good speed test at
    formatting link
    , but there are others.

  1. Disconnect _ALL_ telephones from the line, including the cordless one, and note any change in speed, in either direction. Keep notes.

  2. Plug the cordless phone back in, and see if your DSL speed changes. Note the change(s).

  1. Repeat for your other phones, one at a time. Report the results.

HTH.

Bill Horne Moderator

Reply to
Adam H. Kerman

Bill, the problem is not that the cordless phone base interferes with ADSL, but that I'm now getting unacceptable sound quality on the cordless phone.

My question was, Does a specialized filter exist for cordless phones that use 43-60 MHz range. It must not be old enough to use 1.7 MHz, as it has 10 channels.

Reply to
Adam H. Kerman

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