Inovonics 525N, Installation & User Manual

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Choose a
TRIP LEVEL:
that is exceeded most all the time with
program audio modulation. This will be the level that the
modulation must drop to and remain below for the duration of
the
ON:
period to activate an alarm. Similarly, audio modula-
tion must be maintained above the
TRIP LEVEL:
for the dura-
tion of the
OFF:
period to reset the alarm. Although
PEAK
MODULATION
is peak-responding display with a quick fallback, a
modest amount of integration has been added to this metric
for alarm activation. This filters impulse noise and sets a rate
for the ‘syllabic’ nature of speech.
NOTE: Audio loss is not a reliable indicator of the station go-
ing off the air. Receiver AGC will bring up random noise when
the carrier fails.
SETTING ALARM TALLY CLOSURE POLARITY
Navigate to
CLOSURE POLARITY
, Menu No. 8. This utility sets
the logic for the three tally output closures.
With this menu on the LCD screen, use the
SEL
buttons to
bracket the condition
[GND]
or
[OPEN]
after each of the three
alarm callouts. Once the condition is bracketed, the
MENU/EDIT
buttons will toggle the rear-panel alarm tally polar-
ity. In the example above,
AUDIO LOSS:
and
OVERMOD:
termi-
nals both go to ground for an alarm.
LOW SIG:
, on the other
hand, has been programmed to sit normally at ground and go
open-circuit for an alarm.
AUDIO MONITOR SETTINGS
Audio Bandwidth
Selection
Synchronous detection recovers amplitude modulation by ‘ze-
ro-beating.’ The RF (or IF) is sampled at the same rate as the
incoming carrier with absolute carrier phase lock. This creates
a virtual final IF frequency of zero.
Overall receiver bandwidth is thus defined in large part by au-
dio filtering that follows the detector. The range of 525N audio
cutoff characteristics permits listening to the program as it
might sound with different transmission audio filtering, or
from the perspective of the wide variety of radios that exist in
the marketplace. Modulation measurements, on the other
hand, are always made with full audio bandwidth. User-