MT-4E Analog and P25 Digital Radio Systems - Daniels Electronics

TEST PORT
SCOPE
100V MAX 100V MAX 100V MAX
CH1
CH2
DVM
MIC
HELP
RETURN
AUDIO I/O
MODE
TAB
SHIFT
BKSP
HOLD
GHI
4
PQRS
7
*
JKL
5
TUV
8
0
MNO
6
WXYZ
9
ESC ENTER POWER
#
125 W MAX
VOLUME
SQUELCH
AUDIO IN AUDIO OUT 1 AUDIO OUT 2
FREQUENCY (MHz)
SWITCH A SWITCH B
REF A D
15 3 15 3 IN
13
5
NORM
OFF
11 7 11 7
KEY TX
9
9
MICMODE
ANALOG
DIGITAL
TX A
USB
CI-RC-4L
RX A
CNTL
BUS
TX B
RX B
PULL DOWN
TO REMOVE
MIC
MADE IN CANADA
MODEL # CODE
USB
RF OUT
CNTL
BUS
A
D
FREQUENCY (MHz)
SQ. DISABLE
NORM
OFF
REF
IN
MADE IN CANADA
MODEL # CODE
RF
IN
FUNCTION
12
1
11
2
10
3
9
4
8
5
7 6
+
VOL METER
-
EXT
SPKR
MADE IN CANADA
OFF
60
Chapter 6: Additional Radio System Tests
Receiver Desense
A Receiver desense test can be performed by connecting an RF Signal Sampler such as the Bird Model
4275 Variable RF Signal Sampler between the receive port of the fi ltering equipment and the receiver
RF IN as shown in Figure 6-3. Ensure the transmitter is connected to the fi ltering equipment and the
transmitter is turned OFF.
Rx Balanced Audio Output
(from pins B26 and Z26)
ABC
1 2
3
DEF
+
-
.
GEN T/R ANT
Audio In
REPEATER
TRANSMITTER
CONTROL
RECEIVER
ON
OFF
SPKR
INT
EXT
SYSTEM REGULATOR
POWER
ON
DANIELS
ELECTRONICS LTD.
DANIELS
ELECTRONICS LTD.
DANIELS
ELECTRONICS LTD.
RF OUT from Tx
to Duplexer
T/R port from IFR 2975
to RF signal sampler
Duplexer to
RF IN on Rx
To Antenna
Figure 6-3: Receiver Desense Testing
On the IFR 2975, recall Daniels setup 1 (Rx_Ana) from your internal drive. Enter the correct RF
frequency, select the MOD TYPE to FM and set it for a 1.0 KHz tone and ensure that the deviation level
is set correctly for your receiver (wide / narrow). Enter the CTCSS tone (if used) and deviation level. In
the System Setup; Jumper Settings area of the Service section on the RSS ensure that the “Subtones
on audio path” selection is set to “Don’t pass”.
Monitor the SINAD meter while slowly reducing the RF carrier level. The RF carrier level can be
reduced on the IFR 2975 and also through the variable RF signal sampler. Note the 12 dB SINAD
point. Now, turn the transmitter to KEY TX and check the SINAD meter for any noticeable drop in
sensitivity. If the sensitivity does drop, increase the RF carrier level on the IFR 2975 until the 12 dB
SINAD point is reached. Receiver desense is the difference between this RF carrier level and the RF
carrier level noted when the transmitter was OFF. The receiver desense gives a relative idea of the
additional isolation required by fi ltering equipment.
Note: other transmitters located at the site can also cause desense.
Maintenance
Guide
MG-001 Daniels MT-4E Radio Systems
www.danelec.com