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Page 4 - Introduction
MF & Time Break Recall operation
REN Values
20AT Approvals
Page 4 - Introduction
MF & Time Break Recall operation
The 20AT uses MF signalling and TB recall signalling only. Contact your telephone
line provider if unsure of the type of signalling you should be using.
During a call, phones can use a recall signal to indicate to the exchange that they
are about to send more digits.
To ring properly when a call arrives all phones draw a small current from the
telephone line. All telephone devices have a REN value, a measure of how many
'current units' they need to ring properly.
Most telephone lines can provide ringing current for a total REN of 4. If the total REN
of all the devices on the line exceeds that value, then some of the devices may not
ring when calls arrive.
If it is necessary to connect more devices to a line than it can support, equipment
exists that can increase the total REN provided by the line. Contact your line
provider for details.
• The 20AT has a REN of 1. It can share the same telephone line as other
telephone devices so long as the total REN does not exceed that of the line
(usually 4). INDeX standard telephone sockets provide a REN of 2.
The apparatus is approved for connection to the PSTN or suitable PBX supporting
DTMF signalling.
The 20AT has been approved for use of the following facilities:
• DTMF signalling.
• Mute.
• Dual level receive volume control.
Any other usage will invalidate the approval of the apparatus if as a result it then
ceases to comply with the standards against which the approval was granted.
This apparatus is capable of 999/112 calls to the emergency services.
MF & Time Break Recall operation
INDeX 11.0 20AT Telephone User's Guide
38DHB0002UKHB Issue 1 (10/05/2004)
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