Kitz Forum

Broadband Related => Telephony Wiring + Equipment => Topic started by: 4candles on February 10, 2017, 01:02:43 PM

Title: Line current experiments
Post by: 4candles on February 10, 2017, 01:02:43 PM

In the recent Using The Phone Re-Sync Modem (http://forum.kitz.co.uk/index.php/topic,19162.msg342327.html#msg342327) thread there was a side discussion on line current. Being of a curious disposition, I carried out some tests. My line is approximately 0.9 km.


Milliammeter and decade box across line
Ohms        mA
0               40
100           40
200           40
300           40
400           40
500           40
600           40
700           40
800           40
900           38
1K             35
1.1            33
1.2            31
1.3            29
1.4            27
1.5            26
1.6            25
1.7            24
1.8            22


DECT phone and decade box
Ohms        mA        V across phone
100           40         11.9
200           40         11.9
300           40         11.9
400           40         11.9
500           40         11.9
600           37         11.5
700           34         10.9
800           32         10.5
900           30         10.1
1K             28           9.7
1.1            26           9.4
1.2            25           9.1
1.3            24           8.8
1.4            23           8.6
1.5            22           8.4
1.6            21           8.2
1.7            20           8.0
1.8            19           7.8


Tele 706 and decade box
Ohms        mA        V across phone
100           40         9.8
200           40         9.8
300           40         9.8
400           40         9.8
500           40         9.8
600           40         9.7
700           37         9.4
800           34         9.1
900           32         8.8
1K             30         8.6
1.1            28         8.4
1.2            26         8.3
1.3            25         8.1
1.4            23         7.8
1.5            22         7.7
1.6            21         7.0
1.7            20         6.8
1.8            19         6.8


When this subject was discussed some months ago, I remember thinking that burakkucat's line current was somewhat anomalous, but looking more closely at BT SIN 351 (http://www.sinet.bt.com/sinet/SINs/pdf/351v4p6.pdf) all becomes clear.

Quote

Future designs of the line interface will aim to reduce the line current in the on-line state to improve the energy efficiency of BT’s network equipment. Some of these line interfaces are already deployed on a relatively small scale and as a result the line current on these lines will become 25 mA in the on-line state for all the voltage values specified in this clause. The wider deployment of such line interfaces in the future will be considered by BT as the need or opportunity arises to replace or update existing equipment.

Quote

February 2005 Editorial changes.  Information added to 3.2 that line current provided by new designs of interface will tend towards 25 mA

Title: Re: Line current experiments
Post by: burakkucat on February 10, 2017, 06:45:31 PM

Thank you for performing those experiments and sharing the interesting results.

My telephony service is provided by TalkTalk (as is my Internet access, being MPF'd) and I have always assumed that my "deviant" line current is a configuration of the TalkTalk MSAN.

[Edited to correct the abbreviation.]

Title: Re: Line current experiments
Post by: tickmike on February 10, 2017, 09:03:22 PM

My line is 4.3km long.

With 50.5v measured the line pair with a Fluke 73 DVM.

Using a AVO 73 set to 75 mA  scale I could only draw 16mA.

If I could remember where my decade box is I could repeat your experiment.