Continue to Site

Welcome to

Welcome to our site! is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Telephone line impedance

Not open for further replies.


Member level 4
Jan 17, 2003
Reaction score
Trophy points
Activity points
telephone impedance

Hi All,

-Is there any web site contain the information a typical telephone line impedance for various country? I'm looking for this info.

-I always think that US line impedance is 600 ohm. But after read the EIA470 spec, I'm a little bit confuse. In section measurement), the test setup using 600 ohm for PABX and 900 ohm for CO. So this seem like CO line in US is 900 Ohm. Can anybody help me to clarify this?


phone line impedance

If I know, telephone terminals in EU are tested under:
off-hook state:
600 ohm+-20% f=300-3400Hz, I=40mA, angle less than 20 grades.
DC resistance is less than 320ohm (I=25mA).
on-hook state:
impedance of ringer circuit: 2-50kohm (probably) at 25/50Hz


telephone line impedance

Normally in most countries, telephone line impedance is 600 ohm. But there are some exceptions like US, Venezuela, Canada that has specifications of 900 ohm. I think there aren't other line impedance for telephony. If you need to make a phone application for a specific country review the laws and specification of this country. Normally, in all the world 600 ohm will work well

phone impedance

Same - I am interested with a question kudjung.
However anybody has not given the intelligible answer!
Therefore I repeat a question:
Is there any web site contain the information a typical telephone line impedance for various country (Including Greece)?

telephone impedance measurement

The impedance you are talking about is the REFERENCE IMPEDANCE in the regulations of that country and it is not the real line impedances in those countries. For your knowledge, the line impedance in audio frequencies is a complex impedance, with an angle close to 45 degrees.
An ETSI article describing twisted pair line impedances in some european countries was posted by me, see: **broken link removed**

phone impedance

Many years ago the impedance and other paramenters of telephone circuits were specified at 5000 radians/sec. Because of theZ = sqrt((R+jwL)/(G+jwC)) structure of the line impedance, at low frequencies the R and C predominate and at high frequencies the L and C.

Each government's telecommunication regualtions should provide deails of the line impedances to design for. This is an area where each country has different, even confilcitong, regulations.

Unfortunatley, the web sites do not contain all of the information in the printed versions of the regulations.

line impedance telephone

Hi all

this quastion is very important for telephone designer so you must nowk first what effect for this impedance if values not as the sanderd

--------if your telephone impedance is greater than standerd this will make echo..
if your telephone impedance is less than standerd this will make
"i think"singing
but you can change you telephone impedance from 900 ohm to 600 ohmby palce 2.2 uf capacitor series with 1.8Kohm resistor between ring and tip
this link for european telecommunication sanderd it is good link
this for good information

and this file

Hi All,

In deal with DTMF measurement, it is closely related to the line impedance.

In EU, it is a complex impedance, and in US it is 900ohm. But in which occasion, we use 600 ohms, please advise?

Not open for further replies.

Part and Inventory Search

Welcome to