Installing and putting a SINAUT modem into operation
5.6 LTOP line transformer with overvoltage protection
Station control system
System Manual, 07/2009, C79000-G8976-C178-07
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Determining the receive level
To determine the receive level, the test mode "Test f
H constant
" must be set on the MD2
modem at the beginning of the trunk line. This modem then sends the upper keying
frequency of the set baud rate constantly on the trunk line. The existing receive level can
then be measured at the end of this trunk line. If the trunk line is a line with one or more
tapping points, all the tapping points in the line must be included in the line (as well as
LTOPs).
Note
When measuring the level, make sure that the 150-ohm (at 9600 / 19,200 bps) or 600-ohm
(at 1200 / 2400 bps) terminating resistor is set at an end point or 6-kohm terminating resistor
at a tapping point. You should also make sure that the line is not grounded during the
measurement since the signal is symmetrical.
The MD2 modem can still received data down to a minimum received level of -43 dB. Which
level is actually present at the reception location can then be checked with an oscilloscope or
level measuring device. If this is not available, the level can also be measured with adequate
accuracy using a normal voltmeter. To help you in this situation, the following table
summarizes the level values and corresponding (approximate) voltage values (U
eff
alternating voltage).
Table 5- 21 Comparison of level and voltage values
Level
Voltage value (AC) Level
Voltage value (AC) Level
Voltage value (AC)
+10 dB
2.45 V
-10 dB
245 mV
-25 dB
43.5 mV
0 dB
775 mV
-12 dB
195 mV
-30 dB
24.5 mV
-3 dB
552 mV
-15 dB
137 mV
-35 dB
13.7 mV
-6 dB
389 mV
-18 dB
97.8 mV
-40 dB
7.8 mV
-9 dB
274 mV
-20 dB
77.7 mV
-43 dB
5.5 mV
5.6
LTOP line transformer with overvoltage protection
Introduction
Copper dedicated lines are highly susceptible to electromagnetic interference. The coupling
of extraneous voltages can be inductive or capacitive, for example due to the effects of
lightning. Direct conductive coupling is also possible due to bad insulation.
The LTOP (Line Transformer with Overvoltage Protection) limits extraneous voltages and
overvoltages to a non-critical level. The floating transformer also provides electrical isolation
preventing coupling of voltages into other cable sections.
