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front-panel OLED menu
Alarm
checkbox.
The
RSSI:
readout displays incoming carrier strength. The nu-
merical value represents the level in dBµV, or dB relative to one
microvolt measured at the antenna input.
Threshold On (dBuV):
is the level that the
RSSI:
must fall to, and
remain below for the
Time On (s):
interval, to trigger an alarm.
The returning carrier must reach the
Threshold Off (dBuV):
and
remain above this level for the
Time Off (s):
period to reset the
alarm.
When setting these alarm parameters, it’s a good idea to note
the
RSSI:
reading over a day’s operation so that you can factor-
in any normal signal fading as a result of atmospheric effects.
The Mute
Function
As already mentioned, an FM receiver will generally output a
high level of FM inter-station hiss when no carrier is received.
This would prevent an FM Audio Loss alarm in the event of a
total transmitter failure.
The JUSTIN 808 incorporates a
mute function that automatically
squelches the off-air FM audio for
a Low Signal condition. This fea-
ture is turned
On
or
Off
with the
Web interface
Mute:
button or
with the
Mute
checkbox on the
front-panel OLED menu. Turning
Mute: On
will assure that both
the
Low Signal
and
FM Audio Loss
alarms will be triggered
should the transmitter fail. Otherwise the
FM Audio Loss
alarm
will respond only to ‘dead air,’ and the
Low Signal
alarm, alone,
will signal a transmitter failure.
