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Confused by BT Inspiration Systemphone behaviour



 
 
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  #1  
Old April 3rd 13, 02:25 PM
daneboomerang daneboomerang is offline
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Talking Confused by BT Inspiration Systemphone behaviour

I know from BT's own FAQ post (http://btbusiness.custhelp.com/app/a...inspiration%3F) that they advise the systemphone is connected to an extension socket and not an extension lead. They advise the reason for this is because the featurephone is terminated in a 6 core cable/plug.

From my own experience I have found that POTs work when connected to the inspiration via an extension LEAD. Systemphones, however, just don't turn on at all. No display, no dialtone, nada.

What I don't understand is WHY! :-)

The featurephone needs 4 cores, two data, two voice. Fine.
A POT needs 2 cores, voice. Fine.

What does the extension SOCKET provide that the extension LEAD cannot, pray?

Thanks!
  #2  
Old August 5th 13, 04:38 PM
Dr.Who Dr.Who is offline
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First recorded activity by TelecomsBanter: Aug 2011
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Quote:
Originally Posted by daneboomerang View Post
I know from BT's own FAQ post (http://btbusiness.custhelp.com/app/a...inspiration%3F) that they advise the systemphone is connected to an extension socket and not an extension lead. They advise the reason for this is because the featurephone is terminated in a 6 core cable/plug.

From my own experience I have found that POTs work when connected to the inspiration via an extension LEAD. Systemphones, however, just don't turn on at all. No display, no dialtone, nada.

What I don't understand is WHY! :-)

The featurephone needs 4 cores, two data, two voice. Fine.
A POT needs 2 cores, voice. Fine.

What does the extension SOCKET provide that the extension LEAD cannot, pray?

Thanks!
From my own experience I have found that POTs work when connected to the inspiration via an extension LEAD. Systemphones, however, just don't turn on at all. No display, no dialtone, nada.

What I don't understand is WHY! :-)

The featurephone needs 4 cores, two data, two voice. Fine.
A POT needs 2 cores, voice. Fine.

Hi,

You are nearly right regarding 2 and 4 cores, but a POT needs 3 wires. Pins 2 and 5 are the line (A and B wires, B wire is -50v and the A wire the earth side). Although polarity is not terribly important on a POT you shoud see -50v on pin 2, to be technically correct. Polarity is relevant on a systemphone.

Now with a POT, pin 3 is the capacitor feed and pin 4 is earth for a recall button, if fitted. Without the capacitor feed, the bell will not ring, hence the need for three wires. With a systemphone the data pair, I believe, is wired on pins 1 and 6, and pins 3 and 4 are simply ignored. This is the difference between an LJU Master (it has the capacitor), and an LJU slave (no capacitor). In a multi-socket installation - one Master and many Slaves, pins 2 - 4 inclusive are all in parallel and the LJU Master provides the capacitor feed to pin 3 on all the sockets, and all phones ring (hopefully).

There is further confusion in that some devices (usually Hayes Modems) converted for USA standards do not use the third wire, but have their own capacitor in the box. Likewise some 'foreign' POTS. These items ane non-conforming to the British System, usually work but can cause excessive side tone, faint transmission, bell tinkle, and dialling errors.

I get this information from the Revelation manual which was the forerunner system to the Insipration. The idea was to make the plug in system universal with only one Line jack unit (LJU)

BT learned their lesson over this with the Herald system, where the data pair was pins 3 and 4, so when you plugged in a POT you got data pulses in your ear via pin 3 on lifting the phone. The way to make the line universal was to add another LJU master in parallel with pins 2 and 5 only and leave pins 3 and 4 disconnected. The LJU slave was for the Herald terminal (4 wires) and the LJU master for the POT (2 wires), but dont plug both in at the same time !!

It was necessary to provide service to a POT simply to provide a fail over for exchange lines to designated extensions during power cuts.

You need a BT extension lead that has the larger flat type cable which extends all 6 wires, not just 4 of them. This applies to the Navigator key system. There may be other systems that put the data pair in pins 1 and 6, but I am not aware of them.

Good luck
 




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