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Description
The PSM-500L is specifically designed to be usable as the remote site modem of a TDMA network
when coupled with a proper "Burst" demodulator at the hub site. Note: As of the time of this
manual the "TDMA burst" mode is a special factory request option and not installed in
standard modems.
Another variation could use both the DAMA (star or mesh configuration) with a concurrent TDMA
system as the monitor/control network for the DAMA. Again the PSM-500 modem is ideally suited for
both modem applications at both low and high speeds.
1.2 Modem Functional Assemblies
The PSM-500 VSAT/SCPC Modem consists of seven main functional elements arranged on three
electronic printed circuit assemblies, as shown in Figure 1-2.
The Main Modem Circuit Assembly consists of the following major assemblies:
1. The Modem digital PSK/QAM modulator with carrier generation in the 50 to 90 MHz
range for standard modem, or 950 to 1750 MHz in the L-Band versions.
2. The Modem digital PSK/QAM demodulator accepting signals in the 50 to 90 MHz range
for the standard modem and 950 to 1900 MHz in the L-Band versions.
3. The Modem microprocessor monitor/control subsystem.
4. The Modem Digital Signal Processor Acquisition subsystem.
5. The Programmable Data Interface. Seven standard data interfaces are built onto the
main modem assembly. The unit can also accept special interfaces via an optional
interface card.
The other two printed circuit assemblies are the Front Panel Control Assembly, and the Power
Supply Assembly.
In addition the main PWB can accept two plug-in sub-assemblies for Forward Error Correction
(FEC). The first subassembly normally contains either the standard Viterbi and Reed-Solomon FEC
set or a combination card containing Viterbi/TCM, Reed-Solomon and either a 4k block size Turbo
Product Codes (TPC) or a 16k block size TPC. The TPC could also be installed alone on a card
placed in the second plug in location. The second location could also be one of a number of FECs
that are be available for the M500, such as FlexLDPC.
The IBS Multiplexer circuitry that was on another daughter card in previous modems is now part on
the main board's FPGAs.
Note in the functional block diagram below that, with the exception of the receive FIFO buffer, there
are complementary signal processing blocks in the transmit and receive paths. Note also that there
are no typical superhetrodyne mixing and filtering blocks. That is because there are none used in the
direct modulation and demodulation scheme used in the PSM-500, sometimes referred to as Zero
IF.
The following sections described more detail on the design of the modulator and demodulator.
Page 1-6
PSM-500/500L/500LT SCPC Satellite Modem
PSM-500/500L/500LT - Rev. 0.91
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