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1.4.2 SSPA Module
The amplifier module performs the core function of the unit. An isolator is at the RF input to
ensure good voltage standing wave ratio (VSWR). The RF signal then passes through an
electronically controlled attenuator that adjusts the overall attenuation according to the user input.
After some amplification, a second attenuator is automatically controlled via a look-up table to
maintain the amplifier gain at a constant level over temperature variations.
The RF signal is then amplified by a multi-stage design that utilizes proprietary combining
techniques to meet the rated power requirements. The output circuitry contains a coupler to
provide a sampled signal for monitoring purposes. A power detector circuit also is included and
the reading can be accessed via remote communication. A high power circulator and load is
located at the output to provide good VSWR and protection from external mismatch.
1.4.3 Cooling System
The LPOD contains a robust heat sink and thermal design to maintain a low operating
temperature. The PS 1 contains one temperature-controlled fan, and the PS 1.5 and PS 2 contain
two temperature-controlled fans that are monitored by the M&C board. The fans draw cool
outside air in across the power supply and specialized heat sink. The amplifier module
temperature is monitored and, if for any reason the amplifier temperature exceeds a safe preset
limit, the amplifier module supply is shut down to protect the unit from thermal failure.
1.4.4 Power Supply
The LPOD features a power supply that is power factor corrected. It supplies several voltages
necessary for the unit to operate:
•
The 10 V power supply output state is controlled by circuitry within the RF module. If the
RF module does not have the –5.8 V supply for any reason, it will not allow the 10 V
power supply to turn on. This protects the power transistors within the RF module from
failure due to improper power supply sequencing.
•
The +24 V output powers the cooling fans, is the source of power for waveguide
switching when the SSPA is used in redundant configurations, and is dropped to +22 V
for LNB bias.
•
The +5.8 V, -5.8 V, +7.8 V and +13.5 V outputs are used to operate the M&C board and
other overhead functions.
1.4.5 LNB Operation
Either LPOD package style may be ordered with an optional internal 10 MHz reference and LNB
converter bias tee. With these options installed, the user has control of the bias tee enable (LNB
On/Off) as well as the DC bias voltage (On/Off).
Introduction
Low Power Outdoor (LPOD) Amplifier/Block Up Converter (BUC)
1–6
Revision 15
MN-LPOD
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