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TTY Line Current Source R&S GH 890 (Option)
1.3.12 TTY Line Current Source R&S GH 890 (Option)
1.3.12.1 Design
The TTY line current source consists of a
printed circuit board and a ribbon cable. Via
the ribbon cable the TTY line current source is
electrically connected to the printed circuit
board A66 in the power supply.
Among others, the line current source contains
jumpers for switchover between single current
(40 mA) and double current (±20 mA).
1.3.12.2 Functioning
(See Fig. 1.16)
The AC voltages of +30 V and >30 V generated
from the 25.6>V secondary AC voltage by
means of rectification and filtering are routed
to the respective constant current sources via
PTC resistors.
The PTC resistors ensure an automatic current
limiting in the case of an overload.
The FSK signal from option IF / AF processor
controls the positive and negative constant
current sources via the respective optocoupler.
Both, the +FSK and >FSK signals, are
galvanically decoupled by these optocouplers.
By means of jumpers the constant current
sources may be switched in parallel (Æ single
current: 0 and 40 mA) or in series (Æ double
current: >20 and +20 mA).
VV
25.6 V
25.6 V
Positive
Constant
Current
Source
Negative
Constant
Current
Source
0 V
+FSK
VV
X3
>FSK
0 V
FSK
+15 V
+30 V
>30 V
Fig. 1.16 TTY Line Current Source R&S GH 890 (Option), Block Diagram
X2
6164.0717.02_01
> 1.29 >
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