G-2
Appendix G: Optimizing Radio Performance For Hostile Environments
Moseley SL9003Q
602-12016-01 Revision J
must be greater than –66 dBm. Add 10 dB more for fade margin then you will want to see
an RSL of at least -56 dBm.
INTERLEAVER
: Bit errors may also result from sources other than traditional RF
interference and Gaussian noise from low signal levels. Some of these noise sources include
microphonics, lightening bursts, ignition noise, and other sources that are basically bursty in
nature. The problem with bursty noise is that it creates large groups of burst errors that
may be too much for the Reed-Soloman error correction algorithm to correct within a single
coded block of data.
To combat this phenomenon, an interleaver within the QAM modem is used to spread out
the error bursts over several coded blocks of data. The larger the interleaver factor the
longer the errors are spread out and therefore fewer errors will occur in any coded block for
any single error burst. This allows the error correction algorithm to operate on smaller
number of errors within each block.
The trade off here for increasing interleaving is added delay. Table G-1 shows the
correlation between interleave setting and delay.
Table G-1. Interleave Setting vs. Delay
Interleave Delay*
(ms)
1 2.6
2 3.7
3 5
4 6
6 8
12 14
* delay is for 1408 kbps data rate
To change interleave length navigate to QAM RADIO – CONFIGURE MODEM – Intrlv. The
factory setting is 3 (5 ms). Just like the QAM mode setting, you MUST change the interleave
setting to match on both transmitter and receiver or the system will not operate.
PRE- & POST- BIT ERROR RATE MENU
: The receiver BER status screen is the most
important indicator of the condition of the link. From the front panel, navigate to QAM
RADIO – MODEM STATUS. The first screen that is shown is the “BER POST” and RSL status.
“Post” refers to post-error correction count, or the bit-error-rate after Reed-Soloman error
correction. This is the actual error rate. It is a long-term error count which reflects every
error that has been accumulated since the last time it was reset by pressing the ENTER
button on the front-panel. The system should be error free (displayed as 0.00E+0) under
normal operating conditions but it is quite reasonable to expect occasional errors due to
external or environmental conditions. For a healthy link the error rate should not drop below
1.0E-10 (about 1 error in 1 hour).
Navigate down one more screen to find “BER Pre”. This is the pre-corrected error rate, or
the error count before error correction has been applied. There will usually be some non-
zero error rate before error correction due to errors caused by non-linearities within the
radio link itself. This is especially true for 64 QAM modulation, which is quite sensitive to
amplifier linearity and amplitude and group delay variations. The 16 QAM modulation is not
as sensitive. Pre-BER is a good indicator of proper circuit operation such as whether the
power amplifier is being driven too hard. An increase of only 1 dB above the factory-
calibrated level can be enough to cause a substantial pre-corrected error increase. For this
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 ...
