Norsonic nor1217, Instruction Manual

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11 Norsonic Nor1217
Instruction Manual
140
130
120
110
100
90
10 m 50 m
100 m 20 m
200 m 500 m
20 kHz
10 kHz
5 kHz dB
Cable length (120 pF/m)
Level
Cables and cable length
The Nor1217 with its preamplifier Nor1209 has excel-
lent driving capability for long cables. The signal output
from the microphone preamplifier will be loaded by the
capacitance of the cable between the microphone sys-
tem and the instrument. The capacitance will increase
proportionally with the length of the cable. A typical
value for microphone cables from Norsonic is 120 pF
per metre. Hence, a cable with length 100 m, will load
the output with a capacitance of 12 nF. For lower fre-
quencies 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 output current. A limited cur-
rent 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 sys-
tem with the normal microphone Nor1225 or Nor1227..