Dante Inovonics 541, Installation & User Manual, Page: 26 / 56

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normally encountered in speech and music waveforms. Con-
sistent discrepancies indicate a possible FM exciter issue.
With an appropriate filter selected (Page 19), these modulation
readings should not be affected by accompanying HD Radio
programs. Great care has been taken in the design of very pre-
cise IF filtering to eliminate false indications of FM-overmod at
any HD carrier-pair injection ratio. Any observed interaction
between analog and digital program channels should certainly
prompt further investigation.
Pilot, 38kHz
and RDS Levels
This next section of the display screen first shows the injection
level of the 19kHz stereo pilot. On an FM station broadcasting
in stereo, Pilot should be a rock-steady reading of about 9.0%.
Composite clipping or other nonlinearity in the transmission
path can cause this reading to ‘bounce’ to a lesser or greater ex-
tent. These level perturbations will show up on the accompany-
ing AM bargraph as amplitude modulation of the stereo pilot.
Early FM stereo exciters generated the FM baseband signal us-
ing analog multipliers, which required calibration to null the
38kHz carrier component. Today’s stereo-gens don’t need this,
yet the 541 includes a readout of 38kHz energy. You shouldn’t
see much action on the 38k bar, yet music heavy in sub-bass
may cause this readout to flicker-on occasionally. A steady-
state reading or a great deal of bass-associated activity may in-
dicate a stereo-gen problem.
The
RDS
readout gives the injection level of the RadioData sub-
carrier at 57kHz. Similar to the stereo pilot, this should be a
solid reading at about 5%. Program audio should not modulate
the amplitude of this reading at all. Variations in RDS level
again suggest MPX transmission path nonlinearity or a problem
with the RDS encoder.
Multiplex
Power
This measurement relates only to European broadcasting Stand-
ard ITU-R BS.412-9, which specifies a limit on the overall r.m.s.
power of the FM multiplex signal, rather than (but in addition