Norsonic nor1218, Instruction Manual

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9 Norsonic Nor1218
Instruction Manual
140
130
120
110
100
90
10 m 50 m 100 m 20 m 200 m 500 m
20 kHz
10 kHz dB
Cable length (100 pF/m)
Level
Cables and cable length
The Nor1218 with its preamplifier Nor1207 has excel-
lent driving capability for long cables. The signal out-
put from the microphone preamplifier will be loaded
by the capacitance of the cable between the micro-
phone system and the instrument. The capacitance
will increase proportionally with the length of the ca-
ble. A typical value for the Nor4531 microphone cable
from Norsonic is 100 pF per metre. Hence, a cable
with length 100 m, will load the output with a capaci-
tance of 10 nF. For lower frequencies there are seldom
problems with long cables. However, when the signal
contains the combination of high amplitude and high
frequency, the capacitive loading will lead to high out-
put current. A limited current capacity will set limits for
the maximum slew-rate for the signal. The figure below
shows the maximum level as function of cable length
and frequency. 20 kHz corresponds to the bandwidth
of the microphone system with the normal microphone
Nor1227 or Nor1228.