To agree with you - I don't remember what the impedence is in Australia, but it isn't 600 ohm.
PaulH On Sunday 15 January 2006 10:16, James Harper wrote: > > That would be called a milliwatt generator. It likely exists in their > > central office, but its typically used by their technicians to ensure > > new installations meet specs and sometimes in troubleshooting. Call > > your > > > telco repair number and see if they will give you the telephone number > > for it. > > I'll try that. 1st line technical support at Telstra are not known for > their ability to provide useful information that isn't in their script. > > > If they won't, you can basically do the same thing by dialing out from > > asterisk on one pstn line coming back in through a second pstn line, > > and > > > using the asterisk milliwatt generator. Or, if you have another > > asterisk > > > system available somewhere, call out through a pstn line to that > > asterisk's > > milliwatt generator. (Obviously its not as good as using a CO > > milliwatt > > > as now you have to take into consideration the loss from the second > > pstn line, but it is a way to get a handle on the transmission loss > > values, etc.) > > Would the txgain on the 2nd line also come into play? I guess if you set > it to zero then you only have to deal with an estimation of the line > losses. > > > > Next, while the TDM400 card has control over the line impedence > > > circuitry, the x100p doesn't. > > > > Are the AU telephone standards the same as US standards (eg, 600 ohm > > impedence)? > > This is a question I've been trying to answer too. I had a look at the > standard phone that Telstra would provide to customers about 5 years > ago, and it has an impedence switch on the bottom to toggle between > 'NORM' and '600', which suggests that 600 ohms isn't the normal > impedence. > > On an au configuration example for the pap2 I have seen on the web, the > impedence is set to '220+820||120nF', which suggests that our standard > here isn't 600. > > > > Does anyone know of an addon device which > > > can do impedence matching on the line, or of a modification to the > > card > > > > (eg component swapping) which could allow some manual adjustment? > > > > Twenty years ago, the telphone companies in the US had several types > > of > > > hardware devices available for impedence matching, line balnacing, > > etc. > > > The devices were used to compensate for several different problems > > that > > > would be too costly to fix through conventional means. I don't have > > any > > > clue where one might find those boxes today since those types of > > issues > > > have essentially disappeared due to the heavy use of fiber, remote > > line > > > modules/units, higher quality cables, and other technology > > advancements. > > > Some older telephony jocks may still have some of these in their junk > > boxes. > > > > Since I don't have a clue what the AU standards are, I really can't > > guess at what might be needed in your particular case. > > > > One such example that was fairly common back then was a simple > > transformer > > > that had two primary windings and two secondary windings. One could > > buy > > > them as 1:1.5 (600 ohm to 900 ohm), 1:1 (600 ohm to 600 ohm), and > > other > > > commonly used impedances. The transformer along with two 2.0 ufd > > capacitors allowed DC to pass through, but changed the impedence from > > one value to another. > > I've thought of using a transformer by itself, but obviously that > wouldn't let the DC signals required for looping through. Could you give > me an ascii schematic? > > > As far as substituting components on a x100p card, I don't believe > > that's > > > realistic. If you can read the part numbers on the chips used on your > > x100p compatible card, its not that difficult to check the chip specs > > to see what impedance value it supports. (For example, Intel and > > Silicon > > > Labs made some of the chips used to interface the winmodem cards to > > the > > > pstn lines. Those cards manufacturered for US sales used a 600 ohm > > chip > > > while those manufactured for other specific countries used a different > > chip to match those country-specific telephony specs.) > > I think I've got a spare x100p so I'll check that one out. It's an ebay > purchase so the chances are it's an import... > > > > Finally, my echo is really really awful early in the call but then > > gets > > > > markedly better, which I assume is a result of the echo training > > done > > > > during the call. > > > > That's probably a valid assumption. Whether its the result of poor > > impedence > > matching or something else is questionable. > > I have since done some checking of calling between the two extensions on > the pap2, and without the pap2's echo cancellation being active, I get > echo there too... and that's with either impedence setting. > > > > Is it possible to grab the echo coefficients after > > > training and use them as a starting point for next time? Or would > > this > > > > vary too much between calls? > > > > It's my opinion your thought process relative to preloading the EC is > > very reasonable, but in the past two/three years, those with the > > ability > > > to code such functions "insist" every call is different in terms of > > those > > > values. I disagree but don't have the programming skills to prove it. > > There is likely to be some middle ground where "some implementations" > > would benefit from it, and a lot more would not. > > I modified zaptel.c to dump out the coefficients on ztdiag (just a > #define, removing a few comments, and updating some out-of-date code). I > then started a call and dumped them out every few seconds. They change > wildly, but a large change of the figures may have very little change in > the actual system behaviour of the ec, so I guess that doesn't tell me > anything! > > I'll try and write some code to be able to retrieve and load the ec > values today, and see what happens. > > After about 20 seconds, the echo is reduced to a quiet and very muffled > echo, which you probably wouldn't notice unless you were listening for > it, and is certainly better than the quality of most mobile phone calls. > > Thanks > > James > _______________________________________________ > --Bandwidth and Colocation provided by Easynews.com -- > > Asterisk-Users mailing list > To UNSUBSCRIBE or update options visit: > http://lists.digium.com/mailman/listinfo/asterisk-users _______________________________________________ --Bandwidth and Colocation provided by Easynews.com -- Asterisk-Users mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
