Appendix G: Optimizing Radio Performance For Hostile Environments
G-3
Moseley SL9003Q
602-12016-01 Revision J
reason the power amplifier output level is accurately controlled and compensated over
temperature.
CHANGING FREQUENCY
: For some types of interference, such as strong co-channel and
adjacent channel signals, the only remedy may be to move the carrier frequency away from
the interference. This is also a good test to locate the cause of the interference.
The frequency is changed from the front panel. See Sections 5.5.1 and 5.5.2 in Module
Configuration for details about programming the transmitter and receiver frequencies.
QAM RATE
: If you have found interference within your passband but cannot change
frequency or install larger antennae, there is still another possibility that may help.
Lowering the QAM mode will increase the receiver’s resistance to co-channel interference.
The lower QAM modes are more robust than the higher mode but at the expense of
increased bandwidth. For instance changing from 64 QAM to 16 QAM will improve sensitivity
and co-channel resiliency by 6 dB but will increase occupied spectrum by 33%. In general
16 QAM is more robust against interference, microphonics, and impulse noise such as
lightning.
To change the QAM rate, navigate to QAM RADIO –> CONFIGURE MODEM –> Mode/Effic.
Switch from 64Q/6 to 32Q/5 or 16Q/4. It is imperative to match the QAM mode on both
transmitter and receiver or the system will not operate. Don’t forget to change both.
NOTE
: When shipped from the manufacturer, the QAM mode is selected for optimal
channel utilization for the particular data rate that the link is using. Changing the
transmission bandwidth is left to the user’s discretion. Exercise caution not to exceed Part
74 bandwidth allocation.
FRONT-END BANDPASS CONSIDERATIONS
: The pre-selector filter that is shipped with
the SL9003Q is a 5-pole inter-digital waveguide bandpass filter. It has been optimized for
lowest loss, high ultimate selectivity, and reasonable cost. The bandpass is 20 MHz, which
was designed to keep the loss consistent between the inside and outside channel
allocations. For most applications this pre-selector should provide the best overall
performance. But for extremely powerful near band interference such as pagers this pre-
selector may not provide adequate protection.
Moseley has a wealth of experience in specifying filters for resolving these types of
interference problem and can offer certain bandpass filters with high adjacent channel
selectivity from stock. Contact the broadcast sales manager for further details.
Summary of Contents for Starlink SL9003Q
Page 86: ...5 22 Section 5 Module Configuration Moseley SL9003Q 602 12016 01 Revision J ...
Page 90: ...6 4 Section 6 Customer Service Moseley SL9003Q 602 12016 01 Revision J ...
Page 110: ...A 10 Appendix A Path Evaluation Information Moseley SL9003Q 602 12016 01 Revision J ...
Page 118: ...D 2 Appendix D Microvolt dBm Watt Conversion 50 ohms Moseley SL9003Q 602 12016 01 Revision J ...