User manual

Appendix G: Optimizing Radio Performance for Hostile Environments G-3
Moseley SL9003Q 602-12016 Revision G
Table 8-10 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 with the QAM mode setting the user 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 to the health 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 ENTER 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 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 hours).
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 isn’t nearly so 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 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 see where the interference lays.
The frequency is changed from the front panel. Refer to Sections 5.6.1 and 5.6.2 within Module
Configuration, for details on programming the transmitter and receiver frequencies, respectively.