Asterisk - less PSTN echo via XP100 clone or ATA?

Hi,

As the subject says, which of the above shold give me less echo on PSTN
calls?

Many thanks

Matthew

 

Sorry shold = should.

Must use prevew option more...

 

Matt wrote:
|| Sorry shold = should.
||
|| Must use prevew option more...

or preview, even?

 

Matt wrote:
|| Hi,
||
|| As the subject says, which of the above shold give me less echo on PSTN
|| calls?
||
|| Many thanks
||
|| Matthew

I wouldn't use the XP100 clone for anything other than testing. the call
quality is poor. (Lots of clipping seems to occur, at least for me anyway)

My SPA3000, acting as a SIP trunk, gives me much more flexibility and the
sound quality is great. Obviously, with [email protected], the ZAP (XP100)
channels can receive faxes & forward them by email. I've not sussed out how
to do that yet, with a SIP channel.

 

Ooops. I'll blame that on the 3 hours sleep last night, caused by a
teething 1 yr old.

Matthew

 

The main problem with the X100P clone is impedance matching. Most seem to
be 600ohm US standard. In the UK this gives a lot of echo when the device
tries to transmit to the phone line. The proper Digium card had more
configurable impedance matching.

Peter

 

Would changing a resistor on the card be an option here?

Sparks...

 

If we knew which resistor, i'd give it a try!

Matt

 

Perhaps you could cheat, and put the resistance across/in series with the
line?

 

The BT line and phone have a complex impedance (resistance/capacitance).
See http://www.sinet.bt.com/355v1p5.pdf

The phone terminal impedance is 370 ohm + 620 ohm || 310nf. The network
input impedance is 300 ohm + 1000 ohm || 220nf.

I believe that UK networks are designed as 600ohm. I am not sure of how to
match the two properly. It should be possible with the appropriate circuit,
but I'm afraid I have forgotten my circuit theory. The problem seems to be
mainly with echo being reflected back to the phone (ie X100P clone card)
when it transmits to the line. It seems less noticeable the other way
round.

Maybe there is a good telecoms engineer out there who could come up with a
matching circuit which could go between the card and the phone socket as
part of the interconnecting cable?

Peter

 

Oops... I mean "I believe US networks", not UK...
Peter

 

I've got my ATA set up as that, and it works fine.

Hmm, google for 'vswr matching', perhaps? Also when searching google, try
impedence and impedance as people spell it differently. Or try:

http://www.circuitsage.com/matching.html

http://lists.digium.com/pipermail/asterisk-users/2004-June/052158.html

You can't be the first person who has ever wanted to connect US-spec
equipment to a UK line. There's probably a homebrew circuit diagram out on
the web somewhere. Given that this is also something that applies to
analogue telephony, maybe you could try uk.telecom?

 

X100p cards and their clones dont appear to be configurable for impedence
[one potential source of echo]. So probably an ATA. Another good reason for
using an ATA is that if you're using a SIP provider for DID, you can use
the ATA as a standalone system while taking Asterisk offline to test config
changes etc.