Motorola Gm300 Selling Manual

							Transmit Features2-13
A“Re-Key inhibit duration” can be programmed, which prevents users from re-transmitting a
period of time after the TOT has expired. This prevents an individual user from “hogging” the
channel.
A“De-Key Telegram on TOT”can be programmed to send a telegram when the radio times out.
Benefits

Enforces efficient use of airtime.

Addresses accidental continuous keying.

Re-Key Timer stops users hogging the channel.
6.2 Transmit Admit Criteria
Transmit Admit Criteria automatically check the channel for activity and only allow the radio to
transmit if certain criteria are met. This enforces radio operational discipline and simplifies radio
operation. The Transmit Admit Criteria available are:
Never Allowed -This option prevents the user transmitting and operationally the channel is receive
only.
Always Allowed -This option allows the user to transmit at any time.
Channel Free -This option only allows transmission when carrier is not present.
PL/DPL Lockout -This option only allows transmission when carrier is not present, or
when carrier is present and the radio is detecting the PL decode frequency for the channel.
This option is required for the type of repeater that holds up both carrier and PL during repeater
hang time. Repeater hang time is the period of time during which the repeater remains keyed after a
user’s radio has de-keyed. It is used to prevent other users with different PLs gaining access and
control of the repeater before a ‘called’ radio with the same PL has had a chance to reply.
Past PL/DPL Lockout -This option only allows transmission when carrier is not present, or
when carrier is present and the radio has detected the PL decode frequency for the channel since
carrier was detected.
This option is required for the type of repeater that only holds up carrier (not PL) during hang time,
but where the radios on the repeater use PL. It is used to prevent other users with different PLs
gaining access and control of the repeater during gaps in the conversation.
In this case the called radio, not receiving PL during the hang time, must remember that it did
receive the correct PL prior to hang time and is therefore able to transmit.
NOTECarrier is assumed to be lost when the radio is keyed, so this criterion must be
satisfied again after de-key. 
						

							2-14FEATURES AND BENEFITS
Carrier Gone Timer Expired– This option only allows transmission when carrier has not been
detected for a programmable period of time.
This option is used to prevent operators currently not involved in calls, transmitting over other users
who may be active on the channel, but are de-keyed with their auto-reset timers running.
PL/DPL Not Detected– This option only allows transmissions when carrier is not present, or
when carrier is present and the radio is not currently detecting the PL decode frequency for the
channel.
This option may be used:

To prevent PL users in the same group from transmitting over each other;

If one group is monopolising a repeater, it allows another group to ‘break in’ during
repeater hang time if a PL is also transmitted;

If used on repeaters that transmit PL during hang times, users from other groups can gain
access during the repeater hang time.
Potential problems are:

Should not be used on repeaters that transmit PL during repeater hang time as users
within the same group cannot transmit during this period and this leads to enforced gaps
in the conversation.

A PL user from one group can transmit at the same time as a PL user from another group.
Past PL/DPL Not Detected– This option only allows transmissions when carrier is not present, or
when carrier is present and the radio is not and has not detected the PL decode frequency for the
channel since carrier was detected.
Channel Free or No PL/DPL but Past PL/DPL– This option only allows transmissions when
carrier is not present, or
when carrier is present and the radio is NOT currently detecting the PL decode frequency for the
channel but has detected the PL decode frequency since carrier was detected.
Benefits

Enforces channel discipline.

Prevents improper radio transmissions.

Prevents crosstalk on a shared frequency.

Equal user access when combined with Time Out Timer.
6.2.1 Transmit Admit Criteria not Applied in Auto Reset
It is possible to disable the Transmit Admit Criteria whilst the radio is in Auto Reset.
Benefits

Once a call is set up, the user is always able to transmit during the Auto Reset time, this
means they can always finish their call. 
						

							Squelch Features2-15
6.2.2 Channel Free Beep
If a transmission attempt fails due to Transmit Admit Criteria not being satisfied, a Channel Free
Beep is sounded as soon as the criteria are satisfied.
Benefits

User is advised as soon as they are permitted to transmit; particularly useful on a busy
channel.

Message can be sent as soon as possible.

Don’thavetowastetimere-tryingtotransmit.
7.0 Squelch Features
7.1 Receive Squelch Mode
Squelch settings are used to keep the radio’s loudspeaker turned off unless the required type of
signal is detected. The default squelch mode of the radio when it is first turned on can be set as any
of the following:

Open Squelch (Hear all background noise)

Carrier Squelch (Only open squelch if Carrier is detected)

PL/DPL Squelch (Only open squelch if the correct PL/DPL is received)

Tone Squelch (Only open if the correct 5 tone signal is received)

Tone & PL/DPL (Only open if correct 5 tone and PL/DPL are received)
7.2 PL/DPL Squelch Codes
PL/DPL squelch can be explained to customers as a way to stop them hearing communications
between other users on the same channel who are not in their group (on the same PL/DPL). It
allows several groups within an organisation to share the same channel.
PL codes are often used to access community repeaters.
Each channel can be programmed with separate encode and decode PL/DPL codes.
PL codes can be set between 65 and 255Hz, in 0.1Hz steps.
DPL has 103 codes between 023 and 754.
7.2.1 PL Squelch
PL squelch can be:
Standard: squelch requirements are satisfied when its PL is present
Reverse: squelch requirements are satisfied when its PL is not present 
						

							2-16FEATURES AND BENEFITS
7.2.2 PL Reverse Burst / DPL TOC
A Reverse Burst or Turn Off Code (TOC) can be generated when the PTT is released on a channel
transmitting PL/DPL (respectively). It is sent to indicate the end of transmission to the receiving
radio and so reduce squelch tail.
These are the equivalent of 5 tone Cleardown / Remote Close calls.
Benefits

Different groups in an organization can share a channel

Users dont hear the communications of other groups
7.3 Monitor
Monitor allows the normal Receive Squelch Mode to be temporarily disabled. This allows voice
activity on a channel to be listened to. It is particularly useful in radio systems when a single
communication channel is shared by several different teams of people, as it allows individuals to
check that the channel is free prior to making a call.
7.3.1 Monitor 1 and Monitor 2 Modes
The GM300 Series radios have 2 monitor modes; short press for Monitor 1; long press for Monitor 2.
Monitor 1 disables one level of receive squelch, monitor 2 disables a second level of receive
squelch.
For example,
Example 1 Example 2
Standard Receive Squelch PL Tone & PL
Monitor 1 Squelch (Short Press) CSQ PL
Monitor 2 Squelch (Long Press) Open Open
If the radio is in auto-reset mode, ‘tapping’ the monitor button causes auto-reset to end and put the
radio into receive squelch mode: ie it will end a call. A long press will put the radio into monitor 2
mode.
NOTEOn many community repeaters monitor is not allowed, as users are not allowed to
hear other users’ communications. If this is the case, Transmit Inhibit Criteria can be
used instead. 
						

							Squelch Features2-17
7.3.2 Forced Monitor on PTT (Smart PTT)
It is good radio practice to monitor the channel before transmitting. Forced monitor on PTT enforces
this. The first press of the PTT or a call button puts the radio in monitor mode. The second press of
the PTT or call button actually make the radio transmit. This is Forced Monitor ‘Always’.
Forced Monitor ‘Only if Channel Busy’ is aSmart PTT. It only enters monitor mode if there is
channel activity; if there is no channel activity the radio is allowed to transmit on the first PTT or call
button press.
Benefits

Allows squelch codes to be temporarily disabled.

Forced monitor enforces good radio practice.

Forced monitor is an easy way to monitor channel for activity prior to transmitting.

Encourages users not to transmit over the top of other users.
7.4 Hook Operation
Going “Off-Hook” by taking the microphone out of its hang-up clip makes the radio enter auto-reset
mode, which in turn changes the squelch setting to that defined as the autoreset squelch.
The options available for the Hook are all to do with length of time that the hook function is active. It
can be:

Disabled - (Going Off Hook has no effect);

Permanent - (The function is active for all the time it is Off Hook);

Timed - (The function is active only for the duration of the AutoResetTimer,
even if the microphone is left Off Hook).
The Hook feature is ignored if the radio is in any of the following modes:

Emergency;

Stunned;

Menu.
Benefits

Easy way to monitor the channel for activity prior to transmitting

Timed Hook automatically squelches the radio, so the user doesn’t have to put the
microphone back on the physical hang up switch. 
						

							2-18FEATURES AND BENEFITS
8.0 Accessory Connector
8.1 Dealer Programmable I/O Features
All models of the GM300 Series Professional mobile radios incorporate a dealer programmable
accessory connector as standard.
There are: 4 input lines,
1 output line, and
3 input / output (I/O) lines.
Ta b l e 2 - 3Accessory Connector I/O Features
Pin number
34689101214GM950
External Output Functions:
Carrier Detect 

Ye s
PL/DPL DetectYe s
Radio Busy

Ye s
External AlarmYe s
Per Channel Output

Ye s
Car Radio MuteYe s
PTT Sense

Ye s
Decoder Output ControlYe s
External Input Functions:
Channel SteeringYe s
Hook 
Ye s
Vo i c e P T TYe s
Data PTT
Ye s
Vo i c e & D a t a P T TYe s
Mute Audio PA 
Ye s
Open RX AudioYe s
Public Address 
Ye s
Call 1/2/3/4Ye s
Emergency 
Ye s
Emergency WakeupYe s
Ignition
Ye s 
						

							Accessory Connector2-19
Each programmable pin can be disabled or programmed to a feature. The active state of each pin
can be set as high or low: except

emergency is active low;

ignition is active high.
Benefits

Enables interface to a wide range of external devices.

Customer specific applications can be catered for.

Gives excellent oppor tunities for enhanced dealer added value.

Interface to external Mobile Data Modems.Ta b l e 2 - 4Accessory Connector Pin Out
PinFunction
1Speaker -
2ExternalMic
3Digital In 1 (Ext. PTT use External Mic/ Data PTT use Flat TX Audio)
4 Digital Out 2 (External Alarm)
5Flat TX Audio. Sensitivity 150mV rms to for 60% deviation
6 Digital In 3
7Ground
8 Digital In/Out 4
9Digital In 5 with Wakeup (Emergency)
10 Digital In 6 with Wakeup (Ignition)
11Flat / Filtered RX Audio (Flat RX Audio 330mV rms at 60% deviation
Filtered RX Audio 600mV rms at 60%dev at 1kHz) CPS selectable
12 Digital In/Out 7
13Switched Battery Voltage (max 1A, Dropout Voltage max1V)
14 Digital In/Out 8
15RSSI (Radio Signal Strength Indicator)
16 Speaker +
17Bus+ (used for CPS and Flash)
18 Boot Control
19Reserved
20 Reserved
NOTE
Please refer to the Radio Installation Manual for more information. 
						

							2-20FEATURES AND BENEFITS
8.2 Output Functions
8.2.1 Carrier Detect
The output is asserted whenever carrier is detected and is de-asserted if no carrier is present.
The output is de-asserted if the radio is in TX mode.
8.2.2 PL/DPL Detect
The output is asserted whenever the correct PL is detected.
If PL override is disabled, the output is de-asserted when the correct PL is lost.
If PL override is enabled, the output remains asserted for the AutoReset time after the correct PL is
lost. This is particularly useful when the mobile is used as a base station and needs to remain active
during short losses of RF or PL, eg when the signal is lost for a short moment, or a 5 tone sequence
is sent (many earlier radios cannot encode PL and 5 tone simultaneously).
The output is de-asserted if the radio is in TX mode.
8.2.3 Radio Busy
This output is asserted whenever carrier is detected, or the radio is in TX mode.
8.2.4 External Alarm
If the radio has external alarm enabled and a telegram is decoded that has external alarm enable,
the output is asserted. This output can be used to energise a relay, etc, that will sound the cars horn
and, or flash the lights.
The output is de-asserted when any button is pressed, the radio is stunned or the external alarm
timer expires. The timer is reset each time the output is asserted. For instance, if the external alarm
duration is 5 seconds, and two decodes are received 1 second apart, the alarm starts on receipt of
the first decode, and stop 6 seconds later (i.e., 5 seconds after the second decode).
External Alarm cannot be enabled on decoders set for Stun, Ack1 ringing, Ack1 Answer or Silent
Interrogate.
Benefits

Enables the radio user to be aware of an incoming call when out of, but near to, the vehicle.
NOTEThis feature is not legal in all countries. 
						

							Accessory Connector2-21
8.2.5 Per Channel Output
The output is asserted when the radio is on a channel that has Per Channel Output enabled,
otherwise the output is de-asser ted.
This is used to drive any device which is channel usage specific.
8.2.6 Car Radio Mute
This option is used to mute the audio on a car’s hi-fi system when the two way radio is in use.
The output is asserted if the radio’s loudspeaker is open or the radio is transmitting.
The output is de-asserted if the radio’s loudspeaker has been closed and the radio has not
transmitted during the preceding 5 seconds.
8.2.7 PTT Sense
PTT sense is an output line that follows the internal PTT input line. It is used to give full control of the
transmit function to an external device, eg a computer sending data, so that it can control a user’s
attempts to transmit voice messages.
If PTT sense is programmed, when the internal PTT is pressed, the PTT sense line is asserted.
Note that pressing the mic PTT does not make the radio go into transmit. If the external device is not
transmitting, it asserts the Voice PTT line. It is this that causes the radio to transmit and the audio to
be transmitted.
If the external device is already transmitting, it does not assert the Voice PTT line and the voice will
not be transmitted. When the external device finishes transmitting, it accepts the next internal mic
PTT.
In this application, the audio source must be set to the front microphone, with external voice PTT.
The data source is input on the flat Tx audio line (pin 5), with external data PTT.
If Voice and Data PTT is used (instead of separate Voice PTT and Data PTT), the external device
will not transmit it’s data whilst the audio is transmitting. However, if data is being transmitted, and
the internal PTT is pressed, voice and data will be transmitted simultaneously. This set up will
reduce but not eliminate the possibility of voice and data being transmitted simultaneously, and
hence the data being corrupted.
Benefits

Allows an external device to take control of the transmit function of the radio.

Allows data and audio to be sent from the same radio without clashing. 
						

							2-22FEATURES AND BENEFITS
8.2.8 Decoder Output Control
The output is asserted by the successful decode of a decoder that has Assert Output Control
enabled.
It is de-asserted by the successful decode of a decoder that has De-assert Output Control enabled.
This option is enabled/disabled per personality. This function can be useful for simple telemetry
applications.
Benefits

Allows remote control of external device.

When used in conjunction with external call switch, gives simple telemetry.
8.3 Input Functions
8.3.1 Channel Steering
Channel steering allows an external device to select a channel, using a parallel interface.
The CPS can configure up to 5 input pins in channel steering mode. On the GM340 there are only 3
pins available and six channels selectable.
The radio software takes the state of these inputs and brings them together to form an N bit value,
where N is the number of pins assigned to channel steering by the CPS and the channel selected is
a result of the binary count obtained from these pins; the least significant bit is assigned to the
lowest pin number that has channel steering assigned to it.
This value is the Channel Steering Index.
If the Channel Steering Index is zero, channel steering has no affect and channels are selected by
normal user inputs.
If the Channel Steering Index is not zero, then the channel is set to the channel that corresponds to
the Channel Steering Index value. If the selected channel index refers to a channel higher than the
number of channels programmed in the radio, the highest available channel is selected.
Any attempts to change channel via user button action are ignored if the Channel Steering Index is
not zero, and the Button Error Alert is sounded instead. This includes the following button actions:

Up/Down.

Memory Channel.

Entering channel numbers via the keypad.
If the Channel Steering Index is reset to zero the radio returns to the last ‘user selected’ channel.
If the radio goes into any Emergency Mode for which an Emergency Revert Channel is defined, the
Emergency Revert Channel takes precedence over Channel Steering.
8.3.2 Hook
External hook performs the same function as microphone hook. This can be a mechanical hang-up
or electrical switch.