— 28 —
Using the Web interface, as shown above, click the top
Alarm:
button to toggle this alarm between
On
and
Off
. From the front-
panel OLED menu, check or uncheck the
Alarm
box.
In this example, once the received peak program level drops
30dB below 100% modulation, and stays below –30dB for 30 se-
conds, an FM Audio Loss alarm will be triggered. The alarm will
reset once the program returns, and remains above –20dB, for
15 seconds.
HD Audio Loss
The
HD Audio Loss
alarm is identical to the
FM Audio Loss
ex-
ample just discussed, and a similar setup routine applies. The
only difference is that a loss of the HD Radio digital carrier pair
will not result in the ‘inter-station hiss’ condition typical of ana-
log FM. Thus loss of the HD carrier will always trigger this au-
dio-loss alarm as well.
AES Audio Loss
This alarm monitors the AES digital audio that is looped-
through the JUSTIN 808. Setup of this alarm is identical to the
other two audio-loss alarms. Loss of the looped-through audio
will always result in one of the other audio loss alarms being
triggered, as the looped audio is being delayed and transmitted,
either as the HD1 program or the FM channel.
Flashing
Alarms
Any front-panel
AUDIO LOSS
alarm LED will flash during the
Time On (s):
interval, and then glow steadily until the alarm re-
sets.
Audio-Loss
Alarm
Considerations
The three audio-loss alarms are peak-responding to program
material, but with a slow ‘fallback.’ They will register even the
briefest program peak, but that peak will take approximately a
full second for the measured value to drop 20dB.
This has implication with respect to setting the thresholds and
alarm on/off times. Most contemporary radio programming
will maintain program peaks close to 100% modulation almost
continuously. One exception is classical music, which may have
extended
pianissimo
passages, though even these will probably
have frequent
peak
values in excess of the –30dB in our exam-
ple above. Another format is ‘spoken word,’ which runs the
gamut from poetry readings to newscasts. This program mate-
rial will have more of a staccato nature with frequent pauses.
In both cases, the threshold levels are probably not as im-
portant as the
Time On (s):
and
Time Off (s):
settings. In general,
a longer
Time On (s):
will prevent extended pauses or low-level
passages from triggering an alarm, and a longer
Time Off (s):
will
give greater assurance that the situation has returned to nor-
mal. Remember, shorter settings may dispatch an annoying
succession of alarms.
Low Signal
The
Low Signal
alarm is keyed to
RSSI:
, the Received Signal
Strength Indicator. This alarm may be programmed to alert
staff to a drop in power, to an unexpected receive-path issue,
or to a total transmitter failure. This alarm is similarly enabled
or disabled by clicking on the Web interface
Alarm:
button or
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