Section 3. Operation
3-7
before the VOX HOLD TIME expires (typically one second), the transmitter
unkeys. The Model 30 then begins watching for either VOX or mobile activity.
Simplex Sampling
When the Model 30 is connected to a radio that switches very fast between
transmit and receive (and is not working through a repeater) the Sampling mode
may be used. There are two parameters that affect sampling modes, they are the
SAMPLE RATE and the SAMPLE WIDTH times. This mode begins with the
transmitter keyed up and audio passing from the telco to the mobile. When the
SAMPLE RATE timer expires, the transmitter is unkeyed and the SAMPLE
WIDTH timer is started. When the SAMPLE WIDTH timer expires, the Model
30 looks for carrier detection. If carrier is not present, the transmitter is re-keyed
and the cycle starts again. If carrier is present, telco to mobile audio is shut down
and mobile to telco audio is opened. Audio is passed from the mobile to the telco
until COR drops and the COR HOLD timer expires; the cycle starts again.
Sampling with VOX to Extend Sample Interval
This mode is identical to SIMPLEX SAMPLING, but the Model 30 looks for
VOX indication also. When VOX is up, the SAMPLE RATE is extended to 4
times the normal sampling time. When the Model 30 detects VOX, the telephone
is speaking, and therefore sampling only needs to happen 1/4 as often.
Intelligent Simplex Mode
When the Model 30 is not working through a repeater (not connected to a control
station), the Intelligent Simplex mode will provide the best possible operation.
This mode uses VOX, the SAMPLE WIDTH timer and audio delay to provide
premium simplex operation. As long as VOX is detected, the transmitter is keyed
and audio is passed from the telco to the mobile. When VOX drops for the
SAMPLE WIDTH time (or more), the Model 30 allows the rest of the audio (still
trapped in the delay) to go out the transmitter. Once the audio is out the
transmitter and silence (the gap) is being transmitted, the transmitter is unkeyed.
Just before the end of the gap reaches the transmitter, carrier is checked. If carrier
is present, the mobile takes over the call. If carrier is not present, the transmitter
is again keyed, and the remaining audio in the delay is allowed out the
transmitter. Using the delay and timing the gap, the Model 30 is capable of
sampling between words without the loss of telephone audio. THIS MODE IS
ONLY AVAILABLE WHEN THE OPTIONAL DIGITAL VOICE DELAY
HAS BEEN INSTALLED.
Simplex Phone Key Control
VOX operation may now be bypassed and transmit & receive can be controlled
by the phone caller using the “*” and “#” keys on a DTMF phone set. Pressing
the “*” momentarily will key the transmitter and the caller may talk. Pressing the
“#” momentarily will unkey it. This allows trained callers to have very positive
control in simplex dispatch operations.
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