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the signal discontinuity at the loop junction and provides an analysis virtually indistin-
guishable from the original direct analysis.
In Fig.5.7, the direct analysis from 30 to 1000Hz with 3,16 Hz bandwidth took 12 min-
utes (deterministic signal, linear sweep). Using the Digital Event Recorder, a frequency
transformation ratio of 1 00 was used with playback at a rate of 500 kS/s. The range for
analysis is then transformed to 3kHz to 100kHz with 316Hz bandwidth to give the
same resolution. The sweep rate is then limited by the fastest averaging time available
from the 2010 (0, 1 s) and the resulting analysis is 10 times faster than that of Fig.5.7
(a)
.
A similar rate of analysis was used for Fig.5.7. (c) with the Gaussian Impulse Multi-
plier added.
Further benefits which can be obtained by using the Digital Event Recorder 7502 for fre-
quency transformation are:
a.
The ability to analyse with a narrower effective bandwidth than that normally possi-
ble with the 201 0.
b.
Where a tape recording of field measurements is to be made for later analysis, the
recording required in the field need only be as long as the required data sample
rather than the normal analysis time
.
c.
A short section of a signal may be studied in detail.
d.
Very low frequency signals may be transformed upwards into the frequency range of
the Analyzer.
5.4.2. Impulse Analysis
A similar technique to that of section 5.3.1. may be used for the analysis of single im-
pulses. In this case, however, the time domain weighting is no longer necessary, except
possibly for the suppression of noise in the recording (assuming the initial and final sig-
nal levels to be zero). The technique and theoretical background of impulse analysis is
given in B & K Application Note No
.
1 2-230
"Measurement
of the
,
Energy Spectral Den-
sity of Short Duration Impulsive Signals". Full details are contained in this Application
Note of the technique and the practical use of the 2010 and 7502.
63
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