User manual

Appendix G: Optimizing Radio Performance for Hostile Environments G-1
Moseley SL9003Q 602-12016 Revision G
Appendix G: Optimizing Radio Performance
For Hostile Environments
INTRODUCTION
When shipped from the factory the SL 9003Q defaults are optimized for high-sensitivity, high
spectral efficiency, and low-delay. But hostile RF environments with nearby paging transmitters,
strong co-channel and adjacent channel interference sources, lightening, and unlicensed ISM
band may require a more aggressive configuration.
The SL9003Q continues in Moseley’s reputation for robust radio products that handle difficult
environments. The SL9003Q can be configured for optimal performance from the benign to the
most brutal environments directly from the front panel. The following discussion will show the
user how to configure the frequency, front-end attenuator, QAM mode, interleaver, and pre-
selector for best results and tradeoffs that result.
FRONT-END ATTENUATOR
The first place to start is with the front-end attenuator. The receiver has a 20 dB variable pin-
diode attenuator in front of the pre-amp to protect the receiver from overload when faced with
strong in-band and out-of-band undesired signals that find their way past the pre-selector filter.
This attenuator is controlled from the front panel under QAM RADIO –> RX CONTROL to one of
three modes, ON/ OFF/ AUTO.
AUTO: (Factory default) In this mode the front-end attenuation is controlled by a
leveling loop that begins to insert attenuation in front of the pre-amp when the
input signal exceeds –28 dBm. It continues to increase attenuation with
increasing input signal up to –8 dBm. In general this mode insures that your
receiver will operate with greatest sensitivity and yet provide protection against
occasional interfering signals.
OFF: This mode disables the attenuator completely. Use this mode if strong
bursty interfering signals are sporadically triggering the attenuator leveling control
and causing errors (this is a fairly low likelihood).
ON: This mode forces the attenuator on essentially placing a 20 dB pad in front
of the pre-amp. This mode provides the greatest continuous protection against
interference but also eats up 20 dB of threshold and fade margin. Use this mode
if your received signal exceeds –43 dBm or when strong continuous interferer(s)
existing in-band cause bit errors.
It should be emphasized that it is not necessarily only high-level adjacent channels that cause
interference. There are many combinations of signals that can give rise to intermodulation
distortion, which cause the resultant product to fall within the desired passband.