Midian DDU-300, Instruction Manual

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M
IDIAN
E
LECTRONICS
I
NCORPORATED
P
AGE
5
DDU-300 Manual Rev. 2006.02.22
trunking system. If not using LTR, leave this
unconnected.
3.2 J
UMPER
S
ETTINGS
There are two user configurable jumpers, JU1 and
JU4. Both are installed at the factory. JU1 allows
signaling audio to be heard in the local speaker. If this
is not desired, cut JU1.
JU4 controls the output impedance of transmit audio.
See OUTPUT LEVEL below to determine if JU4 will
need to be cut.
3.3 A
DJUSTMENTS
Once the unit has been connected to the radio, several
adjustments must be made to achieve proper
operation. It will be necessary to open the unit. Use the
pictorial to identify the location of the following trim
pots: R2 and R32 near connector P3, R51 near IC U6,
and R105 near the volume control.
INPUT LEVEL
Use a service monitor to generate a 1000 Hz test tone
at 2/3 of maximum system modulation (typically 3.3
kHz). Measure the voltage appearing at TP1 and
adjust R2 such that TP1 is at 230mV RMS.
OUTPUT LEVEL
To set the audio output level, adjust R51 such that
when the DDU sends a data packet, the radio is
modulated just below 100%. To send a packet first
press <SEND> at the
CALL A UNIT
prompt followed
by 4 digits and <SEND>. If the output level cannot be
adjusted low enough, it will be necessary to cut JU4.
This changes the output from low impedance to high
impedance.
MICROPHONE GAIN
If an optional microphone is installed, the microphone
audio level must be adjusted. Cause the unit to go
into transmit mode by holding down the <SEND> key.
Speak loudly into the microphone at a normal
distance. Adjust R105 such that maximum system
modulation is achieved at peak voice.
SPEAKER PRE-AMP
Though the DDU has a volume control knob, it also
has an input audio pre-amplifier. While listening to
audio on the channel, adjust R32 so that the minimum
and maximum volume control settings are at desired
levels.
PLL ALIGNMENT
PLL alignment is performed at the factory and
normally does not require any adjustment. In the
unlikely event PLL alignment is required, the
procedure is as follows:
1) Ground Pin 9 of U8.
2) Observe Pin 4 of U8 with a frequency counter
or an oscilloscope.
3) Adjust R28 until Pin 4 is at 19.6 kHz.
4) Remove ground from Pin 9 of U8.
5) Adjust R26 until Pin 4 is at 27.6 kHz.
3.4 C
ONFIGURATION
S
ETTINGS
Once adjustments have been made, it will be
necessary to configure the DDU to meet the system
requirements. This is done via Menu Mode.
Be sure to set the time of day via TIME SETUP once
the DDU is operating as desired. Once the time is set,
be sure to leave the unit on at all times or else the
time will have to be reset. The time can only be set to
the nearest minute. Seconds are kept track of
internally and start running the instant the unit is
turned-on. It is a good idea to check the time clock
monthly as crystal and temperature variances affect
the accuracy.
4 BASIC OPERATION
4.1 D
ISPLAY
M
ODE
The DDU operates either in Display Mode or Menu
Mode. In display mode, the DDU normally displays the
last ANI received.
4.1.1 Reading the Display
ID (ANI) – This is the numeric ID (or ANI) of the user
who last transmitted on the channel. When an
emergency ANI is received, this area will alternate