| Initiating a Call
When both repeaters are in standby mode, a user calls on the input
frequency using either CTCSS and/or a 1750Hz Tone-burst. The repeater
responds to this by transmitting the call on it’s output frequency,
including a CTCSS tone. The remote repeater detects the CTCSS tone on it’s
link input and transmits the call on it’s output frequency. Both
repeaters are now relaying the callers message and are in the ‘accessed’
state. When the caller drops carrier, this is detected by the local
repeater and signaled to the remote repeater by dropping the CTCSS tone
on it’s output. Both repeaters now send a ‘pip’ and wait for a
reply. If no reply is made both repeaters send their ID’s and close
down.
Answering a Call
When responding to a call a user may call on either repeaters input
frequency when the control units are in the ‘accessed’ state. The
repeater which receives the reply retransmits the signal and also
injects a CTCSS tone on the output. The remote repeater detects the
CTCSS and also retransmits the reply. Both repeater control systems
reset their ‘time-out’ timers and allow the QSO to continue. When
the caller drops carrier this is detected by the local repeater and
signaled to the remote by dropping the CTCSS tone on its output. Both
repeaters respond by sending a ‘pip’ and wait for a reply. If no
reply is made both repeaters send their ID’s and close down. If a
reply is detected than the above sequence is repeated. Time-out events
are handled by both repeaters independently but in synchronism as each
control unit has identical time-out values.
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Independent Operation
In the event that the local repeater receives a call while relaying a
call from the remote repeater, the control unit will give priority to
the local input for the period that the local input is active. Should
this transmission contain a valid access sequence (CTCSS and/or
Tone-burst) then this shall be interpreted as a de-link command and the
local repeater will revert to conventional operation. The remote
repeater will be unaware of this state but will continue to operate
independently. This facility is intended to allow situations where both
repeaters can operate independently if required. Link mode will be
re-established once there has been no detected activity for a given
period.
Identification
Both repeaters shall uniquely identify their transmissions in
accordance with current requirements. Identification tones from the
remote repeater will not be retransmitted via the local repeater, a
narrow band notch filter will be incorporated in the linked audio path
to accomplish this. In order to identify that linked audio is being
transmitted, the remote repeater shall replace the ‘pip’ at the end
of the over with a ‘K’ (linK-through).
Safeguards
The intelligence within the control units will be sufficient to
prevent anomalous operation, in particular, audio loop-back from the
remote repeater will not be allowed to re-enter the local repeater. The
use of the regionally allocated CTCSS tones will prevent the link
receivers detecting an interfering repeater output. Additionally, the
antennas used for the link receivers at each site will be directional,
minimising the risk of interference. |
