MDS 05-3438A01, Rev. F
MDS 4790/9790 Series I/O Guide
91
MDS 4790/9790 Simplex Radios—With Antenna
Switch Modules
Simplex radios do not have a duplexers. In its place, an Antenna Switch
Module is placed to switch the antenna system between the radio’s
transmitter and receiver. The switch does not have any frequency-sensi-
tive elements and covers the radio’s entire operating band. You can pro-
gram radios equipped with this module to any frequency within their
operating range. However, two things must be considered:
1. The antenna system’s performance might not be satisfactory on the
new frequency. You can quickly check this by measuring the
antenna system’s standing-wave-ratio (SWR) for a ratio of 1.5:1 or
less at the antenna.
2. The receiver’s front-end helical coils will need retuning if the
change in receive frequency is more than 5 MHz.
Figure 44. Antenna Switch Module
MDS 4790/970—Front End Helical Coil Alignment
Changing the radio’s receive frequency by more than 5 MHz requires
re-alignment of the receiver’s front-end helical coil set. Significant deg-
radation in receive bit-error rate (BER) is likely if the coils are not
aligned properly.
For assistance, contact GE MDS Technical Support
for details about the tuning procedure.
8.5 Testing and Removing an Internal Duplexer
Testing
If you suspect that the internal duplexer is not functioning properly, per-
form the following steps to determine if requires replacement:
1. Measure the RF power out of the antenna jack.
If the power registers approxi37 dBm (5 watts), the internal
duplexer is probably functioning correctly (see
Table 21 on Page 103
for dBm-volts-watts conversion chart).
If the power registers significantly less than +37 dBm, proceed with
Step 2.
2. Open the radio chassis, locate the TX cable, and disconnect the
cable from vertical interface board (
Figure 45 on Page 92
).
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