Inline Telephone Amp

Does the phone work OK when the ADSL modem is disconnected?

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson
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Does "quiet" mean low volume?

Sounds like the modem either (1) sucks loop current, or (2) has a low input impedance at audio frequencies (not likely).

You might post your wiring drawings on alt.binaries.schematics.electronic

Maybe you have a fundamental wiring error (likely :-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

ADSL works by assuming that a standard POTS phone will ignore any signal power above audio frequencies (3kHz or thereabouts). I suspect that your cordless phone assumes that there won't be any power above 3kHz and has an active AGC circuit that is wide open to ADSL frequencies while I suspect that your regular phone has the old MOV-style AGC that uses loop current to establish the phone's gain correction. Since the wireless phone can't tell the difference between the ADSL energy and regular "regular" energy it cuts the _total_ energy down, taking your audio with it.

If this is the case then a low-pass filter should clear up your problems, but it must:

  • Not have too much DC resistance, so loop current and ring current pass unmolested,
  • Be able to pass ring current without getting so unhappy it sends up smoke signals,
  • Not present a low impedance to the line at ADSL frequencies and
  • Be bidirectional, so incoming and outgoing energy is treated more or less the same.

To do all of this you either need a fancy active circuit that splits the signal with a hybrid, conditions the incoming audio, leaves the outgoing audio alone, then puts it all back together for the phone with another hybrid while regenerating ring signals. You could maybe get away from regenerating ring signals if you cut all the active stuff out when you're on hook, but that's even more complexity.

As an alternative you could use a passive low-pass filter that passes ring signals, blocks high frequencies while presenting high impedance, and passes audio. It would look something like this:

___ ___ Tip o----UUU---o---UUU---o----o Tip | | | | To Line --- --- To Phone . --- --- | | ___ | ___ | Ring o----UUU---o---UUU---o----o Ring created by Andy´s ASCII-Circuit v1.24.140803 Beta

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Unfortunately if you needed cutoff at 3kHz you'd need huge inductors. So the big question is what cutoff frequency you need to use to filter out the ADSL -- and I don't know the answer to that; you'll have to find out. If the ADSL frequencies are high enough this may work (in fact this may be what their ADSL "splitter" is trying to do).

Or you could sell that POS wireless phone on ebay and get a new one...

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Tim Wescott
Wescott Design Services
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Reply to
Tim Wescott

Well, good grief. If it's under warranty, take it back to the store and tell them it's defective, because you can't hear the guy on the other end.

Good Luck! Rich

Reply to
Rich Grise

snip

If you cant use it, send it back, as you said, its under warranty

martin

Reply to
martin griffith

I would say that it is defective if it doesn't work in a particular application that is not unusual -- e.g., in a place that also uses an ASDL modem. Lose your "engineer" hat, don your "it doesn't work for me consumer" hat.

Reply to
Don Foreman

Have you got a filter on the phone line?

Reply to
Paul Burke

I have a Cordless telephone which is just too quiet to use. It still works well as an answering machine but that's about all. I want to amplify the volume of the phone without ending up spending more than I did to buy the phone in the first place. The outgoing volume is fine.

I know you can get inline phone amplifiers for about ~$30 but all the ones I found were designed to sit between the base of a phone and the receiver, and so wouldn't work with a cordless phone. I also don't know if any of those devices are compatible with Australian phones/lines.

As far as I can see, one of the easiest ways would be to open up the receiver and put a small amplifier there for the speaker itself. But, the phone is still under warranty for a while yet, and I don't want to void it unless I have to (it's not much use at the moment.)

I think another way would be to put an inline amplifier between the wall and the phone's base. I don't know how difficult or costly that would be, but I would like to consider it as an option.

Any ideas or suggestions would be appreciated.

n0dalus.

Reply to
n0dalus

Hello,

If your normal phone doesn't exhibit an amplitude drop with the DSL modem turned on but the cordless does, then the cordless phone isn't working properly IMHO. No matter what their tech support says. I would return it.

None of our cordless phones has ever done that in a similar setup. We could start pondering what the engineers might have done wrong on that cordless phone, like an AGC in the amp that catches DSL carriers or whatever. Bottomline is that it should not do that.

Regards, Joerg

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Reply to
Joerg

I don't think there's anyhing defective about the phone. It is a result of having it on the same phone line as an ADSL modem (I'm not sure why... my non-cordless phone isn't affected.) Other people I know have similar problem with their cordless phones when their ADSL is connected. When I contacted the company about it they said that they had seen it lots of times before and that I should buy their brand of ADSL line splitters instead, and that there was not much I could do about it. One of my friends had the same line splitter that they recommended, so I swapped with him but the problem remained. Unfortunately as the phone is still functioning properly so I can't return it, otherwise I would.

n0dalus.

Reply to
n0dalus

The phone works perfectly when the ADSL modem is turned off. I don't know why the standard phone works fine, but the cordless phone is just really quiet. Naturally I have tried swapping the cables around etc, but wasn't able to solve the problem. Maybe the standard phone has an inbuilt normalizer or an amplifier to compensate for the signal strength being shared between two devices.

n0dalus.

Reply to
n0dalus

There are filters for each device except the modem itself (which shouldn't have one.)

n0dalus.

Reply to
n0dalus

Yes. The volume is so low that the phone is effectively useless.

An ASCII representation of my wiring goes like this:

+------ ADSL Modem | Phone line ---+-----+---[ADSL Filter]--- Cordless phone | | +---[ADSL Filter]--- Normal phone

n0dalus.

Reply to
n0dalus

I would, but unfortunately the phone itself is not damaged or defective in any way. I have tried to explain the situation in my other posts.

n0dalus

Reply to
n0dalus

Well, I had a few cordless phones that exibited the same behavior. Almost all of them had in the base and/or handset a set of variable resistors, and one is recieve and another is transmit volume adjust. It is, of course, very risky at best to go and adjust them with no manual or diagram, but if you have the patience and can be very careful to draw the original position of the pots, and have a good ear to test with- both near and far end- you can get a bit of improvement. You may find you end up with too much sidetone out of the deal, but that's something you may have to live with. I did it with the Plantronics small headset phone, I think it is model CT-10, and I was able to improve the transmit level (people were complaining I was too quiet) as well as the receive volume. Be very careful you don't mess with the RF section, make tiny adjustments and listen for change, and document everything so you can go back to stock, and a good tweaker can do it. Good Luck.

Reply to
Swingbridge-M

Given that OP is in Australia, the terms to use back at the store are "refund", "merchantable quality", "consumer protection" and "Current Affair", in that order. Volume and/or pitch of voice can increase when moving down the list but it isn't strictly necessary. :-)

Cheers.

Ken

Reply to
Ken Taylor

The fact that your normal phone works and the cordless doesn't means that the cordless is "not suitable for the intended purpose" a phrase which exists in consumer protection law in Australia. Do as others suggest and take it back where you got it and use the phrase I gave as your reason for return. They will get the picture.

Reply to
Ross Herbert

I had a similar problem with my answering machine when I went to ADSL. The answer(for me) was to make a small low pass filter.

I ended up using a 600:600 Ohm transformer with both the primary and secondary centre tapped. I put the primary in series with one leg of the line and the secondary in series with the other leg of the line and then put a capacitor across the centre taps. Crude, but it works.

_____ _____ Line 1 -------UUUUU-----o----UUUUU--------->

Primary | Primary | ___ ___ | | _____ | _____ Line 2-------UUUUU-----o----UUUUU--------->

Secondary Secondary

Alan

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Jenal Communications
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Reply to
Alan

If it's uder warranty and it's not working like a new one it's faulty. send it back.

To avoid embarrasment you could consider a hearing test.

Bye. Jasen

Reply to
Jasen Betts

Is is defective in that it doesn't work where your regular phone does.

Unless it says "not compatible with DSL" or similar on the outside of the box, you are entitled to have it repaired or your purchase refunded.

Bye. Jasen

Reply to
Jasen Betts

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