PSM-500/500L/500LT SCPC Satellite Modem
Maintenance
PSM-500/500L/500LT - Rev. 0.91
Page 4-17
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.
What is the delay from end to end using the PSM-500?
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.
Can I use the PSM-500 to help align the station antenna?
Is an AGC output provided to feed to automatic antenna positioning equipment?
Yes - The PSM-500 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 PSM-500
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.
Where is the “Eye Pattern” test points for the I and Q channel receive signals?
The PSM-500 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.
What happened to the Burst Modulator mode in the PSM-500?
The PSM-500 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 PSM-
500 to work with a specific burst demodulator scheme is an option which requires contacting the
factory for availability.
How do I use the modulator and demodulator functions to invert the spectrum?
These options were added into the PSM-500 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.
How do I use the modulator and demodulator functions to vary the FEC C0 and C1 values?
These options were added into the PSM-500 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 placed closer than the required receive acquisition range. Using this scheme
requires the use of the demodulator search mode.
Intelsat in the latest IESS 308/309 has changed the definition of the C0 and C1 values. This
option allows compatibility with any definition.