Receive: Measure the level on the [11] RECEIVE AUDIO
INPUT (BLUE) lead while receiving a full quieting signal
modulated at full system deviation. Use this level to select R7
and R22 from TABLE 2.
Transmit: The RF generated by the transmitter often makes it
difficult to make accurate measurements for the microphone
circuit. Two methods of measurement are presented, the first
does not always produce accurate results. If method 1 does not
appear effective use method 2.
METHOD 1
Key the transmitter and while speaking loudly into the
microphone, measure the level on the [12] TRANSMIT AUDIO
INPUT (GREEN) lead. Use this level to select R47 and R46
from TABLE 2.
METHOD 2
Disconnect the [12] TRANSMIT AUDIO INPUT (GREEN) from
its connection in the radio. Use an audio signal generator to
inject a 1KHz tone into this lead. Key the transmitter and adjust
the output level from the signal generator to produce 2/3 system
deviation as measured on a service monitor. Un-key the
transmitter and measure the output level from the signal
generator. Use this reading multiplied times 3 to select R47 and
R46 from TABLE 2.
NOTE: In some cases the output level from the signal generator
may be too low for accurate readings, or the level may be
difficult to adjust. In these cases build a resistive divider with
the supplied 7.5K and 15K resistors from the resistor packs.
Don't damage the resistors they may be required as gain
resistors. Connect the 15K to the output of the signal generator,
connect the 7.5K to (-) Supply for the ST-25A, and connect the
junction between the resistors to [12] TRANSMIT AUDIO
INPUT (GREEN). Key the transmitter and adjust the output
level from the signal generator to produce 2/3 system deviation
as measured on a service monitor. Measure the output level
from the signal generator. Use this reading to select R47 and
R46 from TABLE 2.
Don't forget to reconnect the [12] TRANSMIT AUDIO INPUT
(GREEN) lead in the radio.
SYNCHRONIZATION LEVEL:
During cipher transmissions the ST-25A transmits
synchronization information approximately twice per second.
This signal carries no coding information but is necessary for
proper operation. For optimum performance the synchronization
bursts should be adjusted to produce 1/2 system deviation.
After installation is complete, switch to the cipher mode and key
the transmitter. Using a service monitor with an oscilloscope
display, adjust R10 for a peak reading of ± 1/2 system
deviation. Deviation readings made with a deviation meter may
not accurately measure the intermittent synchronization burst
signal. If proper adjustment is difficult or not possible, the
transmit audio gain may be set incorrectly. Repeat the gain
setting procedure for the transmitter using METHOD 2. If
difficulties continue, contact the Selectone Applications
Department for assistance.
PROGRAMMING
Field programming is accomplished with either the ST-905
Keypad Programmer or the ST-907 PC based programmer.
The ST-905 Keypad Programmer must be Version 1.3 or
greater. The version can be found on the bottom of the unit
printed on a small white tag. Version 1.3 will read "V1.3". The
ST-907 version must be Version 3.1 or greater. Version 3.1 will
be displayed as VER 3.1 in the upper right hand corner of the
display screen when running the ST-CONFG program. Older
versions of either the ST-905 or ST-907 will not properly
program the ST-25A
Whether using the ST-907 or the ST-905 there are 6
parameters to be considered for programming. They are:
1. Parameter 0
Initial Synchronization Delay
2. Parameter 1
First Alternate User Code Key
3. Parameter 2
Second Alternate User Code Key
4. Parameter *
Third Alternate User Code Key
5. Parameter 3
Primary User Code Key
6. Parameter 9
Operating Mode
(Switched/Double Click,
Clear/Cipher)
The ST-907 uses the DOS program ST-CONFG and provides
all necessary hookup and programming information as screen
prompts.
To use the ST-905 use the following procedure.
1.
Connect the Red (+) and Black (-) leads of the ST-905 to a
6 to 18 Vdc power source (a 9 Vdc transistor battery is an
acceptable power source.)
2.
Connect the ST-905 to the ST-25A with the supplied cable.
3.
Enter the value desired.
4.
Press * and # simultaneously [*#].
5.
Enter the parameter number.
6.
Repeat steps 3 through 5 for each parameter.
INITIAL SYNCHRONIZATION DELAY
(Parameter 0)
Nine possible entries are available for this parameter. The value
selected determines the delay time the ST-25A will use between
operation of the PTT and Initial Synchronization. Delays are
available in 100mS steps from 50mS to 850mS. The value
entered is the 100's digit of the required delay. For example 0 =
50mS, 1 = 150mS, 2 = 250mS etc. Factory default is 2 or
250mS.
If 9 is entered the delay is set to 1.2 Sec. At the end of this time
period an audible beep is sent to the speaker. The beep
indicates "GO AHEAD" and speak. For most operations the 9
selection will provide the most friendly user interface. However
the beep outputs must be connected for this feature to be
effective.
