As a twenty years+ electronic designer (and a sodding degree in it) in the audio area which is what telephones are, I don't think I need to do that.
It is totally pointless to drive an analogue circuit that low impedance balanced at the sorts of line levels an analogue PABX works at, It adds expense and gives zero performance advantage. Ergo no one will do it.
-- Ineptocracy (in-ep-toc?-ra-cy) ? a system of government where the least capable to lead are elected by the least capable of producing, and where the members of society least likely to sustain themselves or succeed, are rewarded with goods and services paid for by the confiscated wealth of a diminishing number of producers.
Further to the above it is perfectly clear from this
that even the telephone lines running into your property are not balanced. One side is earthed and the other is 'live'...
"...Connect the *grounded* circuit side on the tip, followed by the active battery potential on the ring. In the UK, tip and ring are referred to as the 'A' (earth) and 'B' (battery) wires."
Apologies in the form of a donation to 'help for heroes' will be acceptable.
-- Ineptocracy (in-ep-toc?-ra-cy) ? a system of government where the least capable to lead are elected by the least capable of producing, and where the members of society least likely to sustain themselves or succeed, are rewarded with goods and services paid for by the confiscated wealth of a diminishing number of producers.
If that level of ignorance of basic audio signal handling is typical amongst "Electronic Designer" graduates employed by all those sound card manufacturers, it would certainly explain a whole lot.
I hate to disappoint you but not only is it done, it's been done for almost a century now.
Jesus H. Christ! There you go again! Confusing the central office battery bias superimposed on a balanced line as an indication of unbalance. As far as voice signals are concerned, the A leg connects to earth via one half of a split winding on a high impedance relay[1] and the B leg via the other half of the split winding on the same high impedance relay[1] connected to the negative battery terminal which is effectively a zero impedance connection to the exchange earth that just happens to have a -50v DC offset superimposed upon it.
Both legs of the line are connected to earth by equally high impedance connections which maintains balanced conditions. The fact that the B leg happens to be biased with -50v from a voltage generator (the exchange battery) makes absolutely no difference to this state of line balance. The line is balanced regardless of the DC voltage levels with respect earth that are applied to each leg.
Well, it's your choice. I'm not the one having to apologise.
[1] These days, on modern digital exchanges it will be the equivilent in the from of balanced transformer with split windings to allow the exchange battery to bias the line.-- Regards, J B Good
Wikipedia oversimplifies everything.
Apologies in the form of a donation to 'EFF.org' or 'FSF.org' will be acceptable.
-- For a good time: install ntp
Point of historical order - Bells transmitter created a varying voltage (as his transmitter was basically a moving magnet transducer - essentially the same as a pair of speakers wired back to back) It wasn't terrifically practical as a result.
Modulation of current provided by a battery didn't come until a few years later with the invention of the various forms of carbon microphone, Thomas Edison usually gets the credit for that although I don't think he was the first.
-Paul
-- http://paulseward.com
clearly showing the output is unbalanced.
Thank you for that!
-- Ineptocracy (in-ep-toc?-ra-cy) ? a system of government where the least capable to lead are elected by the least capable of producing, and where the members of society least likely to sustain themselves or succeed, are rewarded with goods and services paid for by the confiscated wealth of a diminishing number of producers.
Actually, it shows that the input is handled by a differential amplifier, supporting a balanced input signal, and the line is driven by a non-inverting buffer and an inverting buffer, providing balanced drive.
No transformers, just an extra *inverter*.
-- -michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon
are you:: a: Illeiterate. b: stupid c: trying to change the subject away fron discussing the loop d: going to shut up an slink away e: going to show me up as one more of the above.
Where does it show that the loop is unbalance?
-- For a good time: install ntp
May I respectfully remind all of you pedants that this is a RPi NG, and the subject is now so far off-topic as to be annoying.
Will you now please stop trying to publicly out-smart one another, and if necessary take it to email, so that the rest of ud can enjoy our lives a bit better.
Cheers
No it doesn't.
sheesh learn some electronics FFS
-- Ineptocracy (in-ep-toc?-ra-cy) ? a system of government where the least capable to lead are elected by the least capable of producing, and where the members of society least likely to sustain themselves or succeed, are rewarded with goods and services paid for by the confiscated wealth of a diminishing number of producers.
It clearly shows that the outputs are unbalanced.
It makes no assumption at all about the inputs being balanced.
(Hint: it is normal practice to connect a differential amplifier to an unbalanced line where the earth may not be as earthed as you would like. That doesn't make the line 'balanced' . Balanced has a particular meaning: on average the two wires will have zero potential with respect to earth)
-- Ineptocracy (in-ep-toc?-ra-cy) ? a system of government where the least capable to lead are elected by the least capable of producing, and where the members of society least likely to sustain themselves or succeed, are rewarded with goods and services paid for by the confiscated wealth of a diminishing number of producers.
Actually, it clearly shows classic balanced line driver and reciever circuit topology.
I sincerely hope your PHd in "Electronic Design" was issued by an internet university. God help us all (in the UK), if such ignorance has been the result of a British University education.
-- Regards, J B Good
I remain totally flabbergasted at your ignorance and intransigence There is not a single balanced output anywhere to be seen.Hint the SINGLE line marked OUT has no equivalent OUT B or any such.
It is clearly referenced to ground.
I dont have Phd I have an MA, from Cambridge university, followed by ten years designing everything from missile systems to discotheques.
You can dis all you want, but I know what I know...
-- Ineptocracy (in-ep-toc?-ra-cy) ? a system of government where the least capable to lead are elected by the least capable of producing, and where the members of society least likely to sustain themselves or succeed, are rewarded with goods and services paid for by the confiscated wealth of a diminishing number of producers.
Please clean up your glasses and look again: The signals to the line come from the pins TF (tip feed) and RF (ring feed), and they *ARE* balanced. You may be misled by the schetchily drawn ringing relay circuitry.
-- Tauno Voipio
Not being familiar with the details of the digital side of the interface, I cannot explain the function of that signal being fed from an op amp that is clearly being driven by a balanced input from the _same_ side of the SLIC as that OUT signal.
All that is being shown is that a balanced signal is being 'tromboned' back to the exchange eqipment side as a unipolar 'OUT' signal. The important point of interest here, is that you've chosen a signal that doesn't involve the line side of the connection which, as you've correctly (if irrelavently) stated...
Irrelavent because this unipolar unbalanced signal has no connection to the subscriber's line circuit. It just appears to be an op-amp element to allow a balanced line signal simply labelled 'IN' to be converted to a unipolar unbalanced signal simply labelled 'OUT', presumably to provide a signal local to the exchange equipment side of the SLIC to facilitate some additional processing function.
Which, in the case of balanced transmission line theory and telephony practice, appears to be bugger all.
Since you seem to have a very strong opinion on this subject, I think it would help to resolve this conflict of understanding if you were to describe the criteria you use for defining balanced transmission lines.
-- Regards, J B Good
Sigh. use of a differential amplifierdoes not imply te signal it is being fed with is BALNCED FFS! Itrsysandrd practice in an IC, thats all.
It certainly exceeds your knowledge. You dont know why a differential amplifier would be used to run off and unbalanced line, you don't know what a balanced line actually means and you can't actually read a circuit diagram.
-- Ineptocracy (in-ep-toc?-ra-cy) ? a system of government where the least capable to lead are elected by the least capable of producing, and where the members of society least likely to sustain themselves or succeed, are rewarded with goods and services paid for by the confiscated wealth of a diminishing number of producers.
C it is then. now f*ck off.
-- For a good time: install ntp
Ok then, explain why a differential amplifier would be used to run off an unbalanced line (what secret knowledge of the +IN and -IN signals do you have that might explain your assertion?)
I'm still interested in knowing how you would define a balanced transmission line. All you've offered so far are assertions that claim PABXes use unbalanced telephone loop circuits without any cogent argument to back up your claim.
When you jump into a discussion with a barefaced statement that is contrary to the 113 year old practice in the telephone industry of the use of balanced line working, you'd better have some convincing argument to backup such a statement if you wish to retain any shred of credibility.
-- Regards, J B Good
your clearly making this shit up. balanced means nothing of the sort,
it's common for balanced signls to be offset from ground by tens of volts. (eg: "phantom power" for microphones)
balanced means the signal of interest appears in equal and opposite parts on the two lines.
with phones that's the audio, the DC supply and the ring voltage don't have any components in the 300-3300Hz telephone audio range.
-- For a good time: install ntp
Look at the other side of the picture where the loop is, labeled "tip" and "ring". that's where the telephone connects. "out" is the output from the audio hybrid it goes the the DTMF detector, crosspoint switch/ADC (etc) inside the PABX
It is clearly irrelevant.
Master of Arts? It seems improbable that the faculty of engineering or science would give an MA
We dis because we know what you know is incorrect.
-- For a good time: install ntp
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.