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DATUM
SYSTEMS
PSM-4900L L-Band IF Satellite Modem
1.0
Introduction
The purpose of this document is to provide a quick start application guide to users already
familiar with Datum Systems M5 series of satellite modems, and as an aid to setting up an L-
Band IF based small station.
The PSM-4900L modem brings all the advantages of Datum System's direct modulation and
demodulation design, superior performance and high digital integration for low cost assembly to
the VSAT station. Because this new modem costs little more than a standard 70 MHz IF modem
and significantly reduces the complexity and cost of the up and down conversion equipment, it
promises to provide a new high in performance per dollar. Two expensive parts of the converter
equipment have however been transferred to the modem – that is the high stability reference
oscillator and the ODU power supply.
A significant aspect of small station design using an L-Band interface modem is that all of the
complexity and "smarts" are contained within the modem itself. The Block UpConverter or "BUC"
and the Low Noise Block DownConverter or "LNB" now each contain a single fixed local
oscillator, not required to tune for operation over the entire satellite band covering all
transponders. The PSM-4900L tunes over an extended range of 950 to 1750 MHz (transmit) or
950 to 1900 MHz (receive) in 1 Hz increments allowing it to access 800 MHz of Transmit RF
spectrum and 950 MHz of Receive RF spectrum without any converter settings.
Aside from the many advantages, using L-Band as an inter-facility link frequency results in the
need to carefully consider the components, frequencies and construction techniques used to
insure proper operation. Part of the purpose of this addendum is to spell out those areas where
special care must be used to achieve a reliable station operation.
For the purposes of the remainder of this document the names, acronyms and meanings used
which may be new for this type modem are:
•
"Modem" - Refers to the PSM-4900L modem capable of both transmit and receive
operation.
•
"IF". The modems Intermediate Frequency used to connect to the Up and
DownConversion equipment.
•
"BUC" – Block Up Converter, Often with an integrated power amplifier for installation
directly to the feed at the antenna.
•
"LNB" – Low Noise Block Down Converter. Includes a low noise RF front end and single
down conversion stage to L-Band frequencies. In a VSAT, especially at low data rates,
this is a significantly better device than the typical free running LNB used for video
broadcast reception. A "data grade" LNB must have very low phase noise and a phase
locked LO for proper performance.
•
"Bias T Mux". This is a device that multiplexes power, IF signals and often a reference
frequency onto a single cable going up to the BUC or LNB.
•
"Terrestrial" side. The Line or data side of the modem.
•
"VSAT" – Vary Small Aperture Station, referring to a station with a small antenna,
typically 1 to 4.5 meters in diameter.
•
"LO" – Local Oscillator frequency used for up or down conversion of RF frequenies.
L-Band IF Application Guide
Application Guide
Page L-Band - 1
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Summary of Contents for Datum Systems PSM-4900L
- Page 1 Introduction The purpose of this document is to provide a quick start application guide to users already familiar with Datum Systems M5 series of satellite modems, and as an aid to setting up an L- Band IF based small station.
- Page 2 L-Band IF Application Guide Differences Between 70 MHz and L-Band Modems Since the PSM-4900L modem is closely based on the design of the PSM-4900 70 MHz modem the vast majority of the operation of these modems is identical. We briefly list the differences between these modems here and further amplify operating differences in the following sections.
- Page 3 MHz receive), so it is also possible to use an LO frequency that allows a single modem and Converter to cover multiple frequency ranges. For example, a 4800 MHz C-Band Low side LO would translate the 950 to 1750 MHz range (available in the PSM-4900L) to 5750 to 6450 MHz. Page L-Band - 3...
- Page 4 L-Band IF Application Guide Transmit Output Power Levels The PSM-4900L has a very wide range of power levels available from the transmit output. This is to accommodate direct connection to a standard BUC including significant cable loss without the need for inline amplifiers or attenuators, and to accommodate transmit combiners. The PSM- 4900L can output from –35 dBm to +5 dBm in 0.1 dB steps.
- Page 5 L-Band IF Application Guide “MOD BUC – Current Max” – Alarm setting for maximum current sent to BUC. Can be used to warn or if the current is above the maximum. “MOD BUC – Current Min” – Alarm setting for minimum current sent to BUC. Can be used to warn if the current is below the minimum.
- Page 6 L-Band IF Application Guide M5 L-Band Modem UC/PA LMR-400 (25 - 200 ft) "BUC" Transmit IF Bias T / MUX 10 MHz OCXO Reference RG6 (25 - 200 ft) Receive IF Bias T / MUX 13/18 V Typical VSAT Configuration L-Band Version MAB 8/12/02 This is not intended as a definitive guide to design of L-Band stations.
- Page 7 LNB Power. Most current data grade LNBs require approximately 15 to 24 VDC at 200 to 300 milli-Amps. The power is typically applied via the receive cable, and removed by the LNB for internal use. The PSM-4900L contains an internal receive Bias T/Mux to apply the power and reference signals to the receive line.
- Page 8 L-Band IF Application Guide handling the exposed end of the transmit cable with power applied. Any BUC voltage represents a possible shock hazard, especially at higher voltages. • Second, when DC power is applied extreme care should be used with test equipment.
- Page 9 / waveguide with indoor converters. The PSM-4900L provides a Type “N” 50 Ohm impedance on its transmit cable and a Type “F”, 75 Ohm receive cable connection. Most BUCs are also 50 Ohm, while most LNBs provide a 75 Ohm impedance and use Type “F”...
- Page 10 Interoperability Between 70 MHz and L-Band Modems Not only is the design and operation of the PSM-4900L modem closely based on that of the PSM- 4900 70 MHz modem, but the units are fully interoperable. Thus a typical system configuration with one or more “Hub”...
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Page 11: Specifications
L-Band IF Application Guide SPECIFICATIONS Parameter PSM-4900L Operating Modes, all programmable: Receive and Transmit Continuous (SCPC), Optional Tx Burst. Transmit IF Frequency Range: 950 to 1750 MHz in 1 Hz Steps. Receive IF Frequency Range: 950 to 1900 MHz in 1 Hz Steps. - Page 12 L-Band IF Application Guide Command and Control Protocol The command and control protocol for the PSM-4900L is virtually identical to that for the PSM- 4900 70MHz IF unit. There are two new commands” shown below. The first new command controls the BUC and the second controls the LNB.
- Page 13 L-Band IF Application Guide Mod BUC, Command [47h], Read Change Flags (L-Band Only) Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7 Byte 0 BucPwr VOut VMin IOut IMax IMin LoFrq Byte 1 Spare Spare Spare...
- Page 14 L-Band IF Application Guide Demod LNB, Command [87h], Read Change Flags (Hybrid & L-Band Only) Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7 Byte 0 LnbPwr Reserved Reserved IOut IMax IMin LoFrq Byte 1 Spare Spare...
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