ARA-1 Operations Manual
INTEROPERABILITY NOW
3-9
3.3.1.1
Radio COR Type
The
Radio COR Type
setting determines which method the ARA-1 will use to determine when
the radio is receiving a valid signal, then the radio/ARA-1 pair will be put into the unsquelched
mode [also called “open squelch”] and send the radio RX audio to the SIP network. The ARA-1
can either use the COR output signal from the radio or use VOX (see Section 3.3.1.3). The COR
output is a control signal from the radio that activates when the squelch opens. If this line is
available, connect it to the ARA-1 COR input and select
ACTIVE HIGH
or
ACTIVE LOW
,
depending on whether this line asserts a voltage when the radio is receiving (active high) or pulls
to ground when receiving (active low). This control line may also be called
COS
or simply
SQUELCHED
or
UNSQUELCHED
.
If the radio does not have a COR output control line, select
VOX
. When the ARA-1 is in VOX
mode, it measures the volume of the sound available in the RX output from the radio. Whenever
this audio exceeds a set threshold, the VOX trips, signaling the unsquelched condition (see
Radio
COR VOX Sensitivity
, Section 3.3.1.3). When using the VOX mode, adjust the squelch on the
radio so that no noise is produced unless the radio is actually receiving a signal. FM radios that
are running at full “open squelch” output a high volume of noise when there is no carrier present,
and this noise will inappropriately trip the VOX function.
NOTE:
The Applications Notes that are provided with radio interface cables
purchased from JPS will identify whether a COR line is available, and if so,
whether its sense is active high or active low.
3.3.1.2
Radio COR Inhibit Time
In some radios, the COR line activates momentarily when the radio reverts to receive from
transmit. Even if a hardware COR line is not being used, the radio may produce a burst of audio
when going from the transmit state to a squelched receive state. This “false COR” can cause
problems in some applications, so the ARA-1 includes a provision to ignore the COR signal for
a specified period of time. In many cases this provision is not needed.
The ARA-1 front panel
CHANNEL ACTIVE
LED is lit whenever the ARA-1 has detected active
COR or its VOX function has been tripped. If this LED flashes whenever the radio drops out of
transmit mode, raise the COR Inhibit time until this no longer occurs. See also
Ping Pong,
explained in
Section 5.7.
3.3.1.3
Radio COR VOX Sensitivity
The
Radio COR VOX Sensitivity
setting adjusts the sensitivity of the audio-activated COR
system, also called VOX (Voice Operated Switch). The sensitivity should be set to the lowest
value that always causes the VOX to trip during speech signals from the radio. Setting to a higher
sensitivity will increase the likelihood that the unit will “false,” that is, unsquelch inappropriately
due to noise or other invalid sounds. Make sure the radio RX audio level is set properly before
you adjust the VOX Sensitivity.