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Installation
6. Modulator AUPC Alarm.
7. Modulator Test Active.
8. Modulator Hardware Fault.
9. Demodulator Signal Lock.
10. Receive Input Level below AGC range.
11. Receive Low E
12. Demod Test Active.
13. Demodulator Hardware Fault.
14. Interface Test mode Active.
15. Interface BER Test Sync Loss.
16. Backward Alarm from IBS multiplexer (if equipped).
The inputs are read by the processor and eight outputs are produced including two alarm relays,
one Modulator , one Demodulator and one Summary alarm LED on the front panel, and a
modulator and demodulator redundancy open collector alarms on the interface card, plus the
redundancy switch request. The summary Alarm LED is the OR function of either of the alarm
relays. The front panel or remote control can be used to select which of the possible alarm
sources are assigned to each of the relays or can individually ignore any of the sources. Some
modems only present alarms based upon a hardware fault in either the modulator or
demodulator. The PSM-500 allows the user to select such items as a low input level or E
activate an alarm. By providing two relays and the configuration options, several alternative alarm
scenarios can be used. The A and B alarm relays could represent a minor and major alarm, or
they could be separated into modulator and demodulator functions, or one could be a summary
alarm while the other is a dry contact input to a redundancy control unit.
2.9.5 Using the Internal or an External Reference
The PSM-500 contains an internal Temperature Compensated Crystal Oscillator (TCXO)
reference which determines the basic accuracy of all modem frequency and rate settings. This
internal reference is a nominal 2.0 ppm stability over normal operating temperature, and exhibits
aging less than 1 ppm per year. This is accurate for most applications, and for example,
produces a worst case transmit center output frequency accuracy of 2.0 X 10
or ±140 Hz (176 Hz at 88 MHz). If this accuracy is not sufficient, or the network operating mode
dictates, an external reference can be used.
The L-Band modem, PSM-500L, uses an Oven Controlled Crystal Oscillator (OCXO) and the
standard unit has a 1 x 10
is necessary because the oscillator can be used as the reference for a BUC.
The external reference frequency is applied at the rear panel BNC connector, J7, at a frequency
of 1, 5, 9 or 10 MHz. Use of the external reference and the reference frequency are selected at
the front panel from the <Unit: Ref – Source>, setting to external which then enables the entry
for <Unit: Ref – Frequency>.
The external reference input does not perform any clean-up of an input other than band-pass
filtering with a pass-band from approximately 1 to 12 MHz. The reference input should therefore
been a low noise source.
2.9.5.1 Reference Calibration
During factory testing and calibration the modem unit is compared to a known in-house reference
and calibrated. A default value is permanently stored representing this factory calibration. The
unit may be offset from this factory value by using the manual tuning or automatic recalibration.
Page 2-22
/N
below threshold.
b
o
-7
stability and 2 to 3 x 10
PSM-500/500L/500LT SCPC Satellite Modem
-7
aging rate per year. The increased stability
PSM-500/500L/500L T- Rev. 0.91
/N
to
b
o
–6
6
X 70 MHz X 10
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