M7/M7L/M7LT Modular Satellite Modem Maintenance
M7/M7L/M7LT - Rev. 0.05 4-15
and select option “0” or “Factory”. From that point you make necessary changes to set the desired
configuration. Once all parameters are set as required the configuration can be saved using the
<Unit: Configuration - Store> control. From there you can always go back to this configuration by
recalling it.
4.7.1.2.2. Why doesn’t my M7 talk to another M7 over the satellite? I have set all the
parameters the same.
Any satellite modem has a significant number of parameters, which are settable in order to achieve
the maximum performance at the least cost. Because there are so many parameters it is possible to
have one unit with a slightly different parameter set than that at the other end of the link. If after
insuring that all parameters are set the same and that the acquisition range is correct and that there
are no interfering carriers; one other method is to take both modems back to the factory default
condition and rebuild the configuration from “scratch”. Use the front panel <Unit: Configuration -
Recall> and select option “0” or “Factory”. You may want to save your current configuration before
resetting to the default.
4.7.1.2.3. What is the delay from end to end using the M7?
The satellite link itself represents a fixed and very slightly variable delay due to the distance of the
satellite from the two stations linked. This delay is approximately 250 milli-seconds. In addition
Appendix A lists the specified fixed and rate dependent delays incurred in the modem’s transmit and
receive processing, including those in the IBS Multiplexer and Reed-Solomon if equipped and
enabled.
4.7.1.2.4. Can I use the M7 to help align the station antenna? Is an AGC output provided
to feed to automatic antenna positioning equipment?
Yes - The M7 has a single analog output that is produced by the main processor and converted to
analog by a D/A converter. The parameter selected for this output can be either the AGC, Eb/No or
Mod CXR Level selected in the <Unit: Monitor - Mode>. The slope and polarity are selected using
the “Zero” and “Full” parameters below this. The signal is available at the rear panel on the J5 Alarm
Connector, pin 5 with the Ground return on pin 6. See Installation Section 2.3.3, “Alarm Connection”,
and Operations Section 3.11 for more information on connection and use of the monitor function.
The AGC has been the classic parameter used for this type of function, but the M7 provides an output
that may be better in most situations. That is the Eb/No, which is a function without the slope changes
and negative signal sense of the AGC signal.
4.7.1.2.5. Where is the “Eye Pattern” test points for the I and Q channel receive signals?
The M7 does not have an analog test point to view the eye pattern. All information at this point in the
receive chain is digital and measured by the modem processor. The result of this measurement is
presented as the Eb/No. If it is absolutely essential to view the eye pattern as analog test information,
contact the factory for availability of a special test fixture for conversion.
4.7.1.2.6. What happened to the Burst Modulator mode in the M7?
The M7 has the basic circuitry necessary to implement burst modulation. The burst demodulation
scheme compatible with the modulation used in the PSM-2100 is no longer manufactured, and there
is no clear standard for implementing this capability. Modifying the M7 to work with a specific burst
demodulator scheme is an option which requires contacting the factory for availability.
4.7.1.2.7. How do I use the modulator and demodulator functions to invert the spectrum?
These options were added into the M7 to aid in building specialized systems which may invert the
spectrum sense of the received carrier. The main cause of this would be an up or down converter
which performs a spectrum inversion.
4.7.1.2.8. How do I use the modulator and demodulator functions to vary the FEC C0 and
C1 values?
These options were added into the M7 to help achieve compatibility with other brands of modems at
the other end of a link. These parameter settings also allow changing the modulation of adjacent
carriers on the satellite so that a demodulator will not lock to them. This has value if the carriers are
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