Modulation technique used over the 2-wire (Tip & Ring) of POTS 6

[john00436]

Hi Gurus,

I have been surfing for some time but am not able to figure out as to which modulation technique is used for voice communication over the two wire i/f from CO (Tip & Ring).

There are places were I find Amplitude Modulation is being used with distinct carriers for Tx & Rx, is it true ????

Any links or docs which could address my concern would be very helpful....

Regds.
John

 

[SYQUEST]

That is what the BELL SYSTEM had before T1 carrier existed and changed everything. Those old analogue carrier systems went by types like: K,L1,L2,L3,L4,L4S,L5,L5E,N1,N2,N3,N4,O,ON,P,P1.

Some of that stuff is very interesting to read about. I still have a library of the "Bell Laboratories RECORD" publication that had lots of articles on some of those systems.

....JIM....

 

[jerryreeve]

If you can find it the linkurt demodulator (spelling is suspect) is probably the best singal source of theoretical data. Linkurt provided a majority of equipment to the US. DCA and I think also to bell.

----------------------------
'Rule 29', "The enemy of my enemy is my enemy's enemy. No more. No less."
----------------------------
JerryReeve
Communication Systems Int'l
com-sys.com

 

[SYQUEST]

Yes, the mention of Lenkurt brings up some memories. The mux we used was the 36A system. That stuff required lots of routine maintenance to keep it in tune! And if it got hot, boy would it drift! Lenkurt was owned by GTE before it was sold to one else. Don't recall who. We replaced most of the 36A with DCS muxes, I forget the model, but the shelves had plexiglas doors. The DCS was far superior to the Lenkurt and stable, except for the electrolytic and tantalum capacitors that kept going out every so offen. One of our techs put together a maintenance package to repair them with a higher grade capacitor that would tolerate more heat and less failures.

....JIM....

 

[ISDNman]

John,

Ah yes, I see you. Yes, two signals can be combined, as I mentioend with regards to mixers.

And yes, the hybrid disucussion now makes sense.

At each end you know what the send signal alone looks like, so using this and a hybris you subtract that from then 2 wire signal.

Back in the dark ages everything was 2 wire. The side tone in your receiver was very loud. This caused people to speak to softly. It was at that point that the "anti sidetone" cirucit was developed. Too little side tone can also be a problem.

On digital sets (which are 4 wire) the side tone must be added deliberately so that you don't talk too loud. Sadly most modern designers have no clue which is why the majority of cell phones have no side tone at all and therefore people yell into their phones.

Best regards

If you ask a better question you will get a better reply. Be specific so we can help!

 

[john00436]

Hi,

Thanks to all for sharing their valuable knowledge & time....

Regds.
John