Southern Avionics Company SD50 Manuel D’Utilisation
SD SERIES TRANSMITTER
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Southern Avionics Company
2.5.1 Filter/Bridge PCB
SLP10002 - The Filter/Bridge PCB
The Filter/Bridge includes a broadband toroidal impedance transformer, a seven pole Butterworth low pass
filter, a broadband RF power bridge, modulation envelope detector and associated level sampling and fault latching
circuitry.
The Impedance transformer receives as input the RF Power Amplifiers Class D output and impedance matches it to
the 50Ohm Butterworth Low Pass Filter, which is configured for optimum characteristics via simple jumpers for the
frequency band in use. The sinusoidal 50Ohm output of the Filter is Fed then fed through the RF power bridge which
reports readings of Forward and Reflected RF Power to the Controller / Monitor. The Controller / Monitor then
normalizes and calibrates the power curve and calculates SWR. Fault latches are also set up to report High reflected
power or RF over-current conditions for immediate action via a fault interrupt structure. A sample of the final RF
output envelope is detected and sent back to the Controller / Monitor where other circuitry derives Vmax/Vmin
information for modulation percentage calculation via Controller / Monitor firmware.
circuitry.
The Impedance transformer receives as input the RF Power Amplifiers Class D output and impedance matches it to
the 50Ohm Butterworth Low Pass Filter, which is configured for optimum characteristics via simple jumpers for the
frequency band in use. The sinusoidal 50Ohm output of the Filter is Fed then fed through the RF power bridge which
reports readings of Forward and Reflected RF Power to the Controller / Monitor. The Controller / Monitor then
normalizes and calibrates the power curve and calculates SWR. Fault latches are also set up to report High reflected
power or RF over-current conditions for immediate action via a fault interrupt structure. A sample of the final RF
output envelope is detected and sent back to the Controller / Monitor where other circuitry derives Vmax/Vmin
information for modulation percentage calculation via Controller / Monitor firmware.