A1. There are so many
options and parameter settings! Where do I start?
The PSM-4900 is highly programmable. This can make the
set-up daunting at first. If you are unfamiliar with the common terms and
modes used in satellite communications you should first refer to Section 2 of
the manual “Installation and Setup”. As a starting point the modem
can also be taken to a default basic set of operating parameters by using the
front panel <Unit: Configuration - Recall> parameter 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. Once a configuration is saved you can always go back to this configuration by recalling
it.
A2. How do I make the
PSM-4900 talk to a xxxx brand modem on the other end of a link?
The PSM-4900 has several new programmable features which
should make this easier than ever. First, where possible if both modems adhere
to Intelsat IESS standards then those defined parameters should be set the
same. Still all modem manufacturers have their own conventions for setting
parameters with no specified standard, so for example some modems may have a
different modulation sense for data bits than others. This would make no
difference between two modems of the same type, but would invert data between
modems of different types on each end of a link. Most items of this type are
programmable in the PSM-4900 modem.
See the "Compatibility" section
below
A3. Why doesn’t my PSM-4900 talk to another PSM-4900
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.
A4. What is the delay from end to end using the
PSM-4900?
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
the M5 Manual, "Appendix A" or this web site in "Tech
Notes/Tech Note 5" lists the specified fixed and rate dependent delays incurred in the
modem’s transmit and receive processing. These include delays or latency in the IBS
Multiplexer, Reed-Solomon and Turbo Product Codes FEC if equipped and enabled..
A5. Can I use the PSM-4900 to help align the station
antenna?
Is an AGC output provided to feed to automatic antenna positioning equipment?
Yes - The PSM-4900 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-4900 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.
A6. Where are the
“Eye Pattern” test points for the I and Q channel receive signals?
The PSM-4900 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.
A7. My PSM-4900 and
PSM-2100 do not agree on the Eb/No parameter with Reed-Solomon codec
installed?
The PSM-2100 was designed before Intelsat IESS 309 added
the section defining how the Eb/No was measured with Reed-Solomon concatenated
coding, and uses a different method. The method is encapsulated in ASIC and
not changeable. Unfortunately the IESS lists two possible methods of computing
the Eb/No with Reed-Solomon. The PSM-4900, being of more recent design,
adheres to both IESS definitions by allowing the reference point to be varied.
The two therefore may read differently, but actually achieve the same
performance. Refer to Appendix RS for more information on setting the
calculation parameter.
If you think that the PSM-4900 modem's performance is
below that of any other commercial modem we would be very interested. In
extensive testing we have found no other modem that can outperform the
PSM-4900 in acquisition time, low Eb/No lock performance or BER vs. Eb/No
performance.
A8. What happened to
the Burst Modulator mode in the PSM-4900?
The PSM-4900 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-4900 to
work with a specific burst demodulator scheme is an option which requires
contacting the factory for availability.
A9. How do I (why
would I) use the
modulator and demodulator functions to invert the spectrum?
These options were added into the PSM-4900 to aid in
building specialized systems which may invert the spectrum sense of the
received carrier. The main cause of this may be an up or down converter which performs a spectrum
inversion.
A10. How do I use the
modulator and demodulator functions to vary the FEC C0 and C1 values?
These options were added into the PSM-4900 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 for certain BPSK symbol oredering. The use
of this option allows compatibility with any
definition.
A11. Does the PSM-4900
have AUPC and AUFC and are they compatible with the PSM-2100?
The PSM-4900 does not have AUFC, but retains the AUPC
from the PSM-2100 type modems. Like the PSM-2100 the built in AUPC (Automatic
Uplink Power Control) can be enabled only if the multiplexer option is
installed or if an external communications channel is provided.
The PSM-4900 AUPC is compatible with that in the 2100
when the PSM-4900 modem IBS Multiplexer is placed in the “Enhanced” mode.
It is not compatible in the “Custom” mode.
A12. How do I set up
the IBS Multiplexer and AUPC Option in the PSM-4900 to be compatible with the
PSM-2100 Modem?
The PSM-4900 Modem is capable of varying the parameters
for the IBS Multiplexer beyond the capabilities of the PSM-2100. To maintain
compatibility with the PSM-2100 specific similarly named options are available
in the PSM-4900. These modes are the “Standard” and Enhanced”
multiplexer operating modes. The 4900’s “Custom” mode is not compatible
with the PSM-2100.
For the AUPC to function and to be compatible with a
PSM-2100 it must be set in the “Enhanced” mode.
A13. How do I set up
the Reed-Solomon Option in the PSM-4900 to be compatible with the PSM-2100
Modem?
The PSM-4900 Modem is capable of varying the parameters
for the Reed-Solomon Codec beyond the capabilities of the PSM-2100. To
maintain compatibility with the PSM-2100 specific similarly named options are
available in the PSM-4900. When enabled the RS FEC Mode should be set to
“IESS-308”. This will automatically set the “n”, “k” and
“Depth” options to 126, 112 and 4 respectively up to 1.544 Mbps. At or
above that rate the PSM-4900 “n”, “k” and
“Depth” options must be manually set to 126, 112 and 4 respectively using
the "Custom" Mode. The 4900’s
“IESS-309” and other “Custom” modes are not compatible with the PSM-2100.
A14. Is Datum Systems' Turbo Product Codes compatible with
that made by other modem manufacturers?
There is an extremely good chance that it is not
compatible for several reasons. First is that there is no standard for
implementation of TPC. Second, Datum Systems spent a lot of time and
development in implementing a full set of TPC parameters (i.e. Rates 1/2, 3/4
and 7/8) and insuring the absolute best performance with no compromises. We
have seen no other TPC implementation that even comes close to ours. Third, because
we have many customers that use our modems in systems requiring low latency we
implemented an alternate "Short Block" mode that reduces the typical
TPC delay by approximately 1/3. Simply put - if you want real TPC with the
best performance you must get our modem.
A15. 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 beginning with
the first version of software which supports TPC (revision # 0.62) a new front panel parameter
has been added showing the current transmit/receive symbol rate.
A16. I am connecting to a Cisco router and the link
does not work. The router status shows an "Up/Down" condition. What
is Wrong?
We have seen this particular case more than once now. The
Cisco router status indication should mean that it sees the Link as
"Up" and the Protocol as "Down", meaning that the link can
communicate but the protocols set in the two routers are different.
A17. What is the proper transmit and receive clock
synchronization method when using the modems to connect two routers over
satellite?
Since the TCP/IP packets being sent by the router
(actually it is usually converted to an HDLC packet for transmission) are
asynchronous in nature the synchronization is easier than, for example, a T1
or E1 line. Each end of the link can be set to a modulator clock source of
"Internal" and a demodulator clock source of "RCV Clock".
Each direction of the link is then independently clocked and relies on the
transmitting modem's internal clock to synchronize the bits from the router.
Back to Top
B1. 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.
B2. Why doesn’t the PSM-4900 front panel act like the
PSM-2100? [and] How do I make it act like the PSM-2100?
The PSM-4900 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.
B3. 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
Manual will always turn the carrier off after a change. This option is set in <Mod:
IF – Mute>. If the carrier is always turned off on a parameter change
the setting described is probably set to
“Manual” mute mode.
B4. Why can’t I
find or see a certain option parameter that is shown in the tables?
Many parameters are only available when another option
has been enabled which requires that parameter. For example, the <Demod:
IF – Sweep Time> parameter is only visible if the <Demod: IF
– Sweep Mode> is set to “Search”. These options are shown in the
tables as gray to indicate this status.
B5. Can I control the
far end modem from the front panel of a local modem?
The PSM-4900 has the ability to control the far end modem
(when linked and locked) from a local modem, but only using the remote control
port. This ability requires the addition of the Multiplexer option. Control
from the front panel is prone to possible mistakes that would lead to
accidentally setting the remote modem in a state that could not be recovered
without going to the remote site.
B6. The far right
“Remote”or "Local" LED is blinking. What does it mean?
The Unit IrDA and Remote Activity parameters allow
setting the local and remote lamps to blink when activity is detected on the IrDA
(Local) and remote (Remote) control ports. The same is possible for the “Local” LED using the Unit
Keyboard Activity control.
B7. I can’t find
the control to disable either the modulator or demodulator function?
This function was originally not available in the PSM-4900. We knew of no
one who used it except accidentally, resulting in return of the modem as
faulty.
NEW INFO. We have found at least one user desiring this
ability, and this
feature has been added in versions 0.50 and later of the PSM-4900 code.
B8. What do the
abbreviations on the front panel LCD Display mean?
See the question in part E. Manual below.
D1. How do I make a
cable to connect to my V.35 (or EIA-530) device?
See the “Installation” Section 2 and Appendix C on
“Cabling Specifications” which shows how to make cables to interface
between the modem’s DB37 connector and other types of common connectors
used.
D2. Where do I get a
“Y” cable to implement 1:1 redundancy?
These may be purchased from Datum Systems or it is
possible to build your own. The connections are discussed in Section 2
“Installation” and shown in Appendix C, “Cabling Specifications”.
D3. Why do I keep getting “sync losses” on my link?
Or why does a BERT test show “sync losses”?
This is usually a sign that some section of the link has
a clock or data inversion. See section 4 of the manual for “Loop” testing
to try to determine where the problem is and correct either the wiring or
change the modem data or clock sense.
D4. Why does the modem occasionally fail to operate with
my DTE equipment, and to correct it I have to invert the data?
The only cause in an otherwise functioning modem for this
symptom is that the differential encoder/decoder is turned off. Modems use the
differential encoding to determine the proper relationship between the clock
and data. If the encoder is turned off the modem has a possibility of locking
to a signal with the wrong phase. For all normal operation of the modem the
Modulator differential encoder and the Demodulator differential decoder must
be “Enabled”.
The Turbo Product Codes (TPC) option does not use the
differential encoder, and when it is enabled the differential encoder and/or
decoder is turned off and the option is removed from the parameter matrix.
D5. How do I use the
built-in Bit Error Rate Test (BERT) set?
See Maintenance Section 4.1.2 of the Manual for
information on using the built-in BERT.
D6. Can I use the
built-in Bit Error Rate Test (BERT) set to test the line or DTE side
equipment?
Yes and No. The BERT is designed to transmit and receive
to the modem side. It is however possible to use two other schemes in certain
cases. First is to use the BERT at the far end modem to generate and/or sink
the BERT test pattern. Second, the local modem can be set into an IF loop-back
mode to use just one side of the BERT at a time. For example a test pattern
can be sent from the receive output by enabling the transmit BERT only while
setting the IF loop-back mode. See Maintenance Section 4.1.2 for information
on using the built-in BERT.
D7. Why doesn’t my
1:1 redundant modem pair switch on certain alarms?
The 1:1 redundancy logic is programmable on two levels.
First is the <Unit: Redundcy – SW Rqst> parameter which selects
whether a switch is requested on all alarms, alarm A and/or alarm B. If it is
set to any options but “On All Alarms” then the particular alarms that are
summed into the A and B alarms are themselves programmable, creating the
second level. See the discussion in section for more information.
D8. My modem is limited to 64 kbps (M4 PSM-2100 type)
or 128 kbps (M5 PSM-4900 type). What's Wrong?
The modem is probably set up for a synchronous RS-232
data interface type. You can find this in the Unit Status column of the front
panel display by scrolling up or down. This is a physical limitation of the
interface type and ICs available at the time of design, and closely follows
industry standards. The other interfaces will all operate up to the maximum
that the modem is capable of.
D9. I am connecting to a Cisco router and the link
does not work. The router status shows an "Up/Down" condition. What
is Wrong?
See question A16 above.
D10. What is the proper transmit and receive clock
synchronization method when using the modems to connect two routers over
satellite?
See question A17 above.
