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Appendix G: Optimizing Radio Performance For Hostile Environments G-1
Moseley SL9003Q 602-12016-01 Revision J
G. Optimizing Radio Performance For Hostile Environments
When shipped from the factory the SL9003Q 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 you 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 consumes 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.
ASSESSING INTERFERENCE : This method is very useful to assess interference at your
STL receiver (especially if you do not have a spectrum analyzer).
Turn OFF the STL transmitter at the studio. At the receiver front panel, navigate to QAM
RADIO –> MODEM -> STATUS. The first line entry "QAM Modem" will indicate the RSL
(Received Signal Level) in dBm. With no interference present the RSL will typically be below
–120 dBm. If this is not the case and RSL is above this level, you are receiving undesired
interference within your STL passband.
For QAM data to be properly demodulated at the STL receiver, the RSL must be greater than
the interference noise floor by the following amounts:
• 21 dB for 16 QAM
• 24 dB for 32 QAM
• 27 dB for 64 QAM
To determine your QAM mode, navigate down five more menus under MODEM STATUS until
you read "MODE". For instance, if your STL is operating in 32 QAM mode (i.e., 32Q) and
your RSL interference is –90 dBm, the minimum signal that your STL receiver can acquire