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OM20 Universal Outdoor Modem
4.1.1 OM20 L-Band Printed Circuit Card
The L-Band Printed Circuit Card consists of an analog modulation function, an analog complex
downconversion, and two wide-band digital synthesizers. The block diagram of the L-Band
Assembly is shown in Figure 4-2.
In the modulator, analog in-phase (I) and quadrature (Q) signals are generated on the Digital
Baseband Printed Circuit Card, routed to the L-Band/IF Printed Circuit Card, and modulated at
the desired frequency. The L-Band modulated signal is then passed through a microprocessor
controlled variable attenuator providing gain control of the output signal.
In the complex downconverter, the signal for demodulation is amplified and sent through a
variable wideband attenuator for AGC. The gain-controlled signal is then passed through a
complex downconverter to a low IF.
L-Band
TxLB
L-Band
RxLB
MN-OM20– Revision 5
DCSA
Switch
Figure 4-2. L-Band Card Block Diagram
Filter
Quadrature
PDA
Modulator
Q AA
Filter
L-Band
Synthesizer
(950-1750)
L-Band
Synthesizer
(950-1750)
Quadrature
Demodulator
AGC
OM20 Theory of Operation
Analog I
I AA
Analog I Inv.
Analog Q
Analog Q Inv.
Demodulator I
Demodulator I Inv.
Demodulator Q
Demodulator Q Inv.
4–2
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