PSM-500/500L/500LT SCPC Satellite Modem
Operation
PSM-500/500L/500LT - Rev. 0.91
Page 3-39
3.10.3 Removal and Replacement of Units in Redundancy Mode
It may be necessary to remove a unit of a redundant pair and replace that unit with another. The
following method performs that function with the minimum disruption to the traffic status. In
overview the procedure is to:
1. Force a switch away from the unit to be removed (if it is currently on-line),
2. Disconnection of cables from the now off-line unit, and
3. Physical removal of the unit.
Replacement is the reverse of this procedure.
3.11 Bit Error Rate Test (BERT) Set Operation
The PSM-500 modem has a built-in BERT that can be individually enabled in the transmit and
receive direction. It is capable of operating with two standard patterns; “2047” and “2^23 –1” and
maintains even complex BER test results. BER test results include BER, Sync Loss, Errored Bits,
Total Bits, Error Free Seconds, Erred Seconds and Total Seconds. Tests can be re-started at will
and run via the remote control and from the front panel.
⇒
CAUTION: Enabling the BER Test set will result in disruption of any traffic currently
through the PSM-500 in the direction that is enabled. BER Tests should not be performed
on a live traffic unit.
The PSM-500 BER Test set can be “pointed” in two possible directions. The normal mode as
available in the PSM-4900 involves the BER transmitting in the direction of the satellite and
receiving from the satellite direction. An alternate mode allows the BER set to transmit and
receive toward the terrestrial data interface or “line” side. The direction is controlled via the
Interface
<Intf: Test – BER I/O>
parameter and can be selected for either “Satellite” or
“Terrestrial”. The Satellite direction looks to the modem as if a DTE is sending and receiving data.
The Terrestrial direction appears to the line as if a DCE device is sending and receiving data.
The use of the BERT is more fully described in the Maintenance Section 4.1.2.
3.12 Analog Monitor Output Operation
The PSM-500 modem has a built-in function to output an analog voltage representing the current
value of one of three internal parameters. These are the receive Automatic Gain Control (AGC)
level, the receive Eb/No and the transmit output power level. Each of these is a digital value
accessible to the main processor, which can output the selected value continuously to the rear
panel Alarm connector via a 16 bit digital to analog converter.
Processor access and control of these signals allows a highly flexible output format tailored to the
user’s requirements. In addition to selecting the parameter value to output the processor allows
control of the “full scale” and “zero scale” output voltage over a range of –10.0 Volts to +10.0
Volts. These two settings can control the output slope (gain and direction) and offset.
To illustrate consider the example of outputting the receive AGC (representative of received
signal level) to automatic antenna positioning equipment. The PSM-500 has a carrier input range
of approximately –20 to –60 dBm. The AGC over this range is a voltage varying from
approximately –5 Volts at the maximum input and +5 Volts at the minimum input. Note that these
voltages can vary with data rate and other factors. The slope of this response is negative relative
to the receive signal level. Next assume that the positioning equipment wants a positive slope
between 0 and +10 Volts, where +10 Volts represents the maximum received signal level. In this
case we would set the
<Unit: Monitor - Full>
to 0.0 Volts and the
<Unit: Monitor - Zero>
to
+10.0 Volts. These settings have the effect of inverting the slope of the AGC signal and applying
an offset of +5 Volts to the output.
