5-10 Radio Programming and Tuning: Transmit MDC Signaling System Modulation Tuning
5.6 Transmit MDC Signaling System Modulation Tuning
There are 2 variations of Transmit MDC Signaling System Modulation Tuning, namely 12.5 kHz and
25 kHz.
5.6.1 Service Monitor Setting
1. Initial setup using the 8920A RF Communications Test Set
a. Connect "RF IN/OUT" port on 8920A to RF adaptor on radio's antenna port using a N-Type to
BNC cable. Connect "AUDIO OUT" on 8920A to "Tx MOD" on test box using a BNC to BNC
cable. Connect the rest according to Figure 5-2. Radio Tuning Setup.
b. On 8920A, select "Tx" under "SCREEN CONTROL".
c. Using the "CURSOR CONTROL", key in the following items:
i. Tune Mode: Auto
ii. Tune Freq: Depends on Tune Mode
• Once "Auto" is selected, the centre frequency is set to the strongest RF signal.
• Once "Manual" is selected, the desired frequency has to be entered manually.
iii. Tx Pwr Zero: Zero
iv. Input Port: RF In
v. Ext Tx Key: Off
vi. AF An1 In: FM Demod
vii. Filter 1: 50 Hz HPF
viii. Filter 2: 15 kHz LPF
ix. De-Emphasis: 750 us
x. Detector: Pk
± Max
xi. AFGen1 Freq: 1.0000 kHz
xii. AFGen1 Lvl: 100 mV
2. Initial setup using the R2600 series RF Communications Test Set
a. Connect "RF IN/OUT" port on R2600 series to RF adaptor on radio's antenna port using a
N-Type to BNC cable. Connect "MOT OUT" on R2600 series to "Tx MOD" on test box using a
BNC to BNC cable. Connect the rest according to Figure 5-2. Radio Tuning Setup.
b. On R2600, select "DISP" under "CURSOR ZONE":
i. Meter: RF DISPLAY
Table 5-4. Transmit MDC Signaling System Modulation Tuning
Channel Spacing (kHz) Tuning Range (kHz)
12.5 1.8 ± 0.05
25 3.6 ± 0.1
Note: Modulation Balancing needs to be carried out prior to MDC Signaling System
Modulation Tuning. Failing to do so will result in the wrong deviation value being
obtained while performing MDC Tuning.
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