Norsonic nor1216, Instruction Manual

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11 Norsonic Nor1216
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 Nor1216 with its preamplifier Nor1209A 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 microphone
system and the instrument. The capacitance will in-
crease 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 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 output current.
A limited current capacity will set limits for the maxi-
mum 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
Nor1225 or Nor1227.