Telephone Wires (Line)

[ElectroEnthusiast]

Can anyone explain me the '2-wire' and '4-wire' wiring in Telephone.
To elaborate, telephone signals reach the phone in two wires, from telephone instrument to receiver it is 4 wires that.

 

[ckshivaram]

check this links

**broken link removed**

 

[FvM]

To supplement the hybrid point, classical telephones have usually a single tapped transformer for the hybrid circuit, like shown here Telephone - Wikipedia, the free encyclopedia

 

[ElectroEnthusiast]

check this links

**broken link removed**

Hi ckshivram,
Can you please explain a bit, i'm new to this topic.

 

[mister_rf]

More details, about how a hybrid transformer suppressing the so called side effect by separate the
microphone and speaker circuit, you may find here:
https://users.utcluj.ro/~dtl/TF/Cursuri/LAB1_eng.pdf

 

[ElectroEnthusiast]

Can Anyone explain this?

 

[kak111]

About Hybrid Transformers and 4-wire transmission...............

http://www.awcsl.co.uk/downloads/hints/hybrid.pdf

**broken link removed**

Hybrid coil - Wikipedia, the free encyclopedia

**broken link removed**

 

[mister_rf]

Just what part didn't you understand? :-D

 

[ElectroEnthusiast]

Just what part didn't you understand? :-D

I've underlined/and boxed the lines which i havent understood.
Where is 4 wire circuit present(inside telephone instrument/ central office-exchange?)?
Does the transmission line here consist of 4 wire?
Basically, please tell me the use of 2 wire 4 wire circuits?

Thanks in Advance.

 

[mister_rf]

Transmission on 2-wire bidirectional path need to include some amplification for enhancing signal transmission.
As the amplification modules are unidirectional need to switch for a 4-wire path, that including two unidirectional paths which include amplification for enhancing signal transmission. In one such electronic hybrid first and second transformers are employed to couple unidirectional amplification stages into the bidirectional 2-wire transmission path. Signals from a first direction are supplied from a first 2-wire path via the first transformer to a first one of the unidirectional amplification stages and, then, via the second transformer to a second 2-wire path. Similarly, signals from a second direction are supplied from a second 2-wire path via the second transformer to a second one of the unidirectional amplification stages and, then, via the first transformer to the first 2-wire path, thereby providing amplification for both directions of transmission on the bidirectional 2-wire transmission path.

---------- Post added at 13:57 ---------- Previous post was at 13:52 ----------

Subscriber lines are two-wire circuits but inside repeater circuits and end of the lines need to switch to 4 wire.
Most analog trunks are fourwire circuits, consisting of two unidirectional two-wire circuits, one for each direction of transmission.


---------- Post added at 14:09 ---------- Previous post was at 13:57 ----------

https://media.wiley.com/product_data/excerpt/87/04716628/0471662887.pdf

 

[ElectroEnthusiast]

---------- Post added at 13:57 ---------- Previous post was at 13:52 ----------

[/COLOR]Subscriber lines are two-wire circuits but inside repeater circuits and end of the lines need to switch to 4 wire.
Most analog trunks are fourwire circuits, consisting of two unidirectional two-wire circuits, one for each direction of transmission.

Why subscriber lines are two-wire circuits? and why there is a need to switch to 4 wire?
Trunks are 4 wire? Whats diff b/w subscriber lines/trunk?

---------- Post added at 14:09 ---------- Previous post was at 13:57 ----------

[/COLOR]https://media.wiley.com/product_data/excerpt/87/04716628/0471662887.pdf

Thanks

 

[FvM]

Why subscriber lines are two-wire circuits? and why there is a need to switch to 4 wire?

1. Because it involves a great saving of cables
2a. Because ear and mouth are separate. (I guess yours too)
2b. During the transmission path for special purposes, as discussed in your book

 

[mvs sarma]

I really appreciate your queries and enthusiasm. after all any modern invention is partly to reduce the cost also. 4 wire extension to customer premises would become costly. in modern technology you are getting broadband on copper. it is virtual 4 wire, as each direction would use one band of frequencies.

On the other hand trunks had to use these Hybrids once upon a time. In modern digital and even electromechanical cross bar switches, it is all 4 wire upto and including the last switch or exchange. Only at the point where the connection turns into copper to serve the customer, it becomes 2 wire.

 

[ninju]

Refer the file that i've attached.

 

[ElectroEnthusiast]

Thanks FvM, mvs sarma, ninja.

In the file attached by ninja, it shows 'Intertoll Trunks' as 4 wired, whereas toll connecting trunks as 2 wired. While both are trunks, why that diff(4wired/2wired)?

On the other hand trunks had to use these Hybrids once upon a time. In modern digital and even electromechanical cross bar switches, it is all 4 wire upto and including the last switch or exchange. Only at the point where the connection turns into copper to serve the customer, it becomes 2 wire.

>Is this the answer?
Thanks sir, i had the same perception about the 2wire/4wire, but had not clearly understood. I came across (the difference in nos of wires) when i had to restore a faulty telephone.

There's some good piece of information in that Book ninja, will have to read it. But, i'm a bit busy to read it now.

 

[mvs sarma]

As you study the case, you would appreciate. In fact 4 wire working up to customer had already come in the shape of ISDN. Later present broadband and voip is all a virtual 4 wire.