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Maintenance
PSM-500/500L/500LT SCPC Satellite Modem
How do I determine the transmitted "Symbol Rate" of the modem?
This particular parameter used to be a lot simpler to define. With the introduction of Turbo
Product Codes coupled with all the other modem modes and options like programmable
IBS multiplexer data load it is now extremely hard to define. The modem knows though,
and it is available at the front panel parameter showing the current transmit/receive
symbol rate. It is in the <Mod: Test – Symbol Rate> and the <Dem: Test – Symbol
Rate> parameters.
A.3 Why does It do that?
The modem is operating fine and then suddenly will not lock!
You probably have the differential encoder/decoder turned off. It is only provided as a control for
very special cases and should normally be set to "Enabled".
The modem changed its operating parameters without me doing anything!
The ACR or Automatic Configuration Recovery feature is possibly enabled by setting one of the
<Unit: Config – Recall X> parameters set to a non-zero value. This will change the modem
configuration if the receive carrier is lost longer than the number of seconds entered.
The <Unit: Config – Power-Up> parameter may be set to change to a specified configuration on
power-up. The normal setting for this is "Last" (0).
B. Front Panel Control
What happened to the "Differential Encoder/Decoder parameter?
In normal operation there is no need to disable the Differential encoder or decoder. We only
found that occasionally someone disabled it and then had problems locking up to carriers, so this
capability was initially removed from front panel control. All of the latest firmware however now
allows this control, so you may need to update your firmware.
How do I enter a number with a minus sign?
At any time during the "Edit" process the "+/-" key will change the sign of the current entry (if the
change is possible). In the quick edit mode this can be the first key pressed, so for instance, if the
current setting for modulator transmit output level is –10 dBm then pressing "+/-, 12" will enter a
value of –12 dBm. You could also press "1+/-2" or "12+/-" with the same result.
Why doesn't the PSM-500 front panel act like the PSM-2100 or PSM-4900? [and] How do I
make it act like the PSM-2100?
The PSM-500 has many more features and programmable options than the PSM-2100 modems.
A close match is achieved by disabling the "quick" entry mode and remembering to press the
"Edit" key first instead of the "Enter" key. Once you become accustomed to the "Quick" entry
mode and using the change sign (+/-) and decimal point keys you will find it more convenient
than any entry on the PSM-2100.
Why does the transmit carrier turn off whenever I make a change?
First the transmit carrier can be set to a mode which will turn the carrier off if any change is made
that would result in a possible interference with other carriers on the satellite. This mode can be
set to one of three states: Automatic, Confirm or Manual. Automatic will turn the carrier off during
the parameter change and return the carrier on (if currently enabled) after the change is
completed, Confirm will ask if the carrier should be left on (requiring a "yes" or "no" answer), while
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PSM-500/500L/500LT - Rev. 0.91
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