23
Call Decoder
The call decoder feature works in conjunction with a Zetron HEAR Decoder and allows
field radios to alert a specific remote or group of remotes. This is useful for cases where
the remote operators wish to hear only those transmissions intended for themselves and
not hear all traffic on the channel. When an incoming call is decoded, the alerted remote
(or remotes) will unmute audio, flash an LE, and (optionally) send an audible alert tone
out the speaker.
The call decoder feature allows maximum flexibility in using a Zetron HEAR Decoder.
The HEAR Decoder decodes over the air DTMF or pulsed tone signaling and translates it
function tones sent to the remotes and/or base station. In some installations, the HEAR
Decoder will be used without the call decoder enabled. In these cases the HEAR Decoder
is responsible for muting and unmuting the base station. An example of this type of system
is one in which the base station is muted by something in addition to the HEAR Decoder,
such as upon CTCSS or DCS signaling.
When the call decoder is used, muting is done at the remote instead of at the base station.
This is typically done in order to selectively unmute individual remotes out of a group
connected to a signal base station. The call decoder feature is also used for installations in
which a visual or audible indicator is necessary to alert the operator of an incoming call.
To use the call decoder feature, the call decoder must be enabled using the ZIPR
configuration software. On a M284, the call decoder may be enabled on a per line basis.
The call decoder is triggered when the remote detects either the group or individual call
alert frequency. These frequencies are programmable to any function tone from 650 to
2050 Hz, and should be programmed with its own individual call alert frequency, and a
group of remotes would share a common group call alert frequency. The remote can also
be programmed to mute receive audio upon receiving a mute function tone, which could
originate from either a HEAR Decoder or parallel remote.
If the call decoder is enabled, the unit defaults to muting receive audio, and receive audio
is muted whenever the handset is placed on-hook. Audio is unmuted when one of the call
alert frequencies is detected, if the handset is taken off-hook, or if the remote initiates any
transmit activity. A key is also usually programmed for Call Decoder Mute, allowing the
operator to manually mute or unmute audio, and providing and LED indication of the
current mute status.
When a call alert frequency is detected, receive audio is unmuted and an LED starts
flashing rapidly. On a M284 the red LED of the corresponding line flashes rapidly, while
on a M280 the Call Decoder Mute LED flashes. The flashing stops when the call is
acknowledged, which happens if the corresponding line button is pressed, the Call
Decoder Mute button is pressed, the handset is taken off-hook, or if the remote initiates
any transmit activity. An optional audible alert can also be sent when a call is decoded.
This alert tone sends a ringing sound for approximately 1 second followed by a 3 second
pause. The alert will continue for a programmable duration of time, or until the operator
presses a key or lifts the handset.
