SIGNALLING UNITS
No's 44B, 45A, 53A and 54A


SIGNALLING UNIT No. 44B

General Description
The Signalling Unit No. 44B is a PBX SSDC5-A to SSAC15-A converter.

Circuit Description
On an outgoing call 'earth-on' and 'earth-off' conditions are generated on the 'M' wire by the SSDC5-A interface card. These conditions are converted by the signalling unit tone generator to pulses of 2280 Hz and transmitted to the distant PBX.
On an incoming call pulses of 2280 Hz are detected by the signalling unit tone receiver and converted to earth-on, earth-off conditions on the 'E' wire. These conditions are transmitted to the SSDC5-A interface card.

Transmission Requirements
The transmission requirements are identical to those detailed for SSAC15A.

Methods of Testing Circuit
The circuit may be divided into two parts:
SSAC15A signals to line - This may be tested as described in the SSAC15A section.
Note:
A high level tone may be sent to line by pressing the 'Send High' button on the signalling unit front panel.
SSDC5A Signals to PBX - This may be tested as described in the SSDC5A section.

Associated Documentation
A full description of the unit is contained in Specification S1382.
Circuit details are available on Diagrams SA/SAW102061, SA 10207 and SA 10208.
The circuit operation is described in diagram notes for SA 10207 and SA 10208.


SIGNALLING UNIT No. 45A

General Description
The Signalling Unit No 45A is a SSDC5-A to SSDC10-A converter. It is used primarily to convert PBX SSDC5-A interface to SSDC10-A and to extend the E&M signalling path of a derived channel on Channel Translating Equipment (CTE) over an audio section to a distant PBX. (CTE working is described in the SSDC5-A section of 'Signalling Systems')
SSDC5-A and SSDC10-A signalling systems are described elsewhere.
Space is provided in the unit for the mounting of one or two transformers as required by the Line Terminating Facility (LTF).

Circuit Description
The Signalling Unit No 45A may be wired to be used as:
2 wire DC5-A connected to 2 wire DC10A
4 wire DC5-A connected to 4 wire DC10A
2 wire DC5-A connected to 4 wire DC10A
4 wire DC5-A connected to 2 wire DC10A

The principles of signalling on all circuits is as follows:-
On an outgoing call, 'earth-on' 'earth-off' conditions are generated on the 'M' wire by the SSDC5A interface card. These conditions are converted by the signalling unit to a combination of CB, reversed CB, loop and earth conditions, which result in current reversals being sent to the distant PBX.
On an incoming call, current reversals are detected by the signalling unit and converted to earth-on, earth-off conditions which are passed to the SSDC5A interface card on the E wire.

Transmission Requirements
The transmission requirements are identical to those detailed in the SSDC10 section.

Methods of Testing Circuit
The simplest method of testing the circuit is to manually busy the circuit by removing the E&M link and putting it into the 'busy' position. This action causes a 1.2k ohm earth to be connected to:
The 'Line' side of the 'E' wire. This condition should seize the DC5A card at the local PBX and busy the trunk.
The 'Equip' side of the 'M' wire. This condition should cause the signalling unit to generate a 'seize' signal over the 2 wire DC10 circuit to call the distant PBX. The 'seize' signal is Battery B/Earth A.

An incoming signal can be checked by asking the operator at the distant PBX to seize the circuit. The Battery B/earth A condition may be measured at either the 'DC10', or 'S+, S-' links.
Note:
When changing the Signalling Unit card it is necessary to wire in the appropriate transformer as it is separate to the signalling unit card.

Associated Documentation
A full description of the unit is contained in Specification S1400. Circuit details are available on Diagram SA100650.
The circuit operation is described in diagram notes for SA/SAW 100650.
The wiring of the front panel is described in Diagram SAW 102840.


SIGNALLING UNIT No's 53A & 54A

General
The Signalling Unit No 53A converts line interface signalling conditions to 1 VF line conditions in accordance with SSAC15C. It is designed to work with a Signalling Unit No 54A. The Signalling Unit No 53A is referred to as the Equipment Signalling Unit (ESU) whilst the Signalling Unit No 54A is referred to as the Instrument Signalling Unit (ISU).

Uses
The signalling units may be used to provide:
LONG EXTERNAL EXTENSION - In this case the 53A must be connected to a 2 wire extension port and the 54A to a standard 2w type telephone.
INTER-PBX WORKING ON KEY SYSTEMS - In this case the 53A can only be used on loop calling exchange lines.
OUT OF AREA EXCHANGE LINE - In this case the line must terminate on:
1. A telephone instrument
2. A PMBX exchange line
3. An incoming only exchange line to a PABX
4. Automatic Call Distribution Equipment that does not require a clear condition from the Public Exchange.

Transmission Requirements
The 2-wire of the Signalling Units No 53A and 54A presents a complex impedance to line which is designed to match BT local cables. The insertion loss will vary with frequency when sending and measuring with instruments terminated in a 600 ohms non-reactive impedance. The performance requirements are therefore given in terms of a nominal loss when the 2 wire line is terminated in a complex impedance to match the signalling unit, and a corrected figure when terminated in 600 ohms non-reactive impedance.
Insertion loss 2-wire to Transmit: Nominal loss 4 dB measured with 600 ohms termination, 2.8 db at 800 Hz (Signalling Unit 54A is 2.5 dB at 800 Hz).
Insertion loss Receive to 2-wire: Nominal loss 4 dB; measured with 600 ohms termination, 4.4 dB at 800 Hz. (Signalling Unit 54A is 4.4 dB at 800 Hz).
Note:
If it is necessary to check or adjust the insertion loss of the Signalling Unit No 54A, then in order to isolate the test equipment from the 2-wire of the Unit, the procedure described below should be followed
1. Transmit Path Insertion Loss: At a frequency of 800 Hz and a send level of 0dBm and with both sending and receiving test equipment terminated in 600 ohms, adjust RV1 until the loss 2-wire to 4-wire transmit is -27 dB plus or minus 0.2 dB. The sender should be coupled into the 2-wire via a 1:1 transformer, (Transformer No 477A or equivalent to isolate the sender and provide a DC loop for the SLIC.
2. Receive Path Insertion Loss: At a frequency of 800 Hz and a send level of 0dBm and with both sending and receiving test equipment terminated in 600 ohms, adjust RV2 until the loss 4-wire receive to 2-wire is -4.7 dB plus or minus 0.2dB. The receive, should be coupled into the 2-wire via a 1:1 transformer, (Transformer, No 477A or equivalent) to isolate the sender, and provide a DC loop for the SLIC.

Associated Documentation - Signalling Unit No53A
A full description of the unit is contained in Specification S1579.
Circuit details are available on Diagram SA/SAW 102990.
The circuit operation is described in Diagram notes for SA/SAW 102990.
Full details of PBX terminating arrangements are shown on Diagram SA/SAW 103240.

Associated Documentation - Signalling Unit 54A
A full description of the unit is contained in Specification S1573.
Circuit details are available on SA/SAW 103000.
The circuit operation is described in Diagram notes for SA/SAW103000.

Methods of Testing Circuit
The 4 wire circuit may be tested by listening on the transmit and receive pairs with a high impedance telephone or other suitable listening device. A high level tone may be induced onto the transmit pair of each signalling unit by pressing the 'send high level tone' button at the appropriate signalling unit.

Notes:
At idle state the Signalling Unit No 54A will be sending a low level tone out on the transmit pair.
You will require a level measuring set if you wish to measure the levels of signals.

A quick local end test of the 54A may be performed by removing the 'transmit' and 'receive' links and inserting one of them into the 'transmit' and 'receive' 'equip' sockets. (Refer to faceplate diagram) This action will cause the low level tone that is sent on the 'transmit' pair to be looped back into the 'receive' pair and so cause the telephone bell to ring.
The 2-wire circuit to the extension or key system may be tested by inserting a test telephone into the 2-wire and dialling into the Signalling Unit No 54A.
The 2 wire circuit to the PBX may be tested by using a meter connected across the 2-wire and ensuring that a loop is sent to the PBX when the Signalling Unit No 53A is seized.

 

 
 
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Last revised: December 19, 2010

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