ETS-Lindgren HI-3603 VLF Survey Meter User Manual
Page 41
HI-3603 VDT/VLF Survey Meter
© ETS-Lindgren, August, 2005
Revision E, Part #H-600042
41
Figure 13: Monitored magnetic field waveform as observed
with an oscilloscope connected to the preamplifier output
jack. Each verticle division is equal to 100 mA/m peak-to-
peak.
Because of the electronic method of broadbanding the magnetic
sensing loop in the HI-3603, there is some distortion of the
measured magnetic field waveform for lower frequency
components. However, for typically encountered CRT retrace
times, this distortion of the waveform is negligible. Figure 4
above illustrates this distortion in the slowly changing part of the
waveform by showing a superposition of the waveform of the
incident magnetic field and the waveform of this field after being
sensed by the broadbanded loop sensor. The applied waveform
used in the measurement was a saw-tooth having a symmetry
ratio of 9:1 at 30 kHz (90 percent of the period is used during the
slow part of the ramp and 10 percent is used during the fall time -
this is typical of VDT waveform symmetry). In the fall time part of
the waveforms, however, the two waveforms lie identically on top
of one another showing good fidelity in responding to this fast
changing signal component.