Specifications

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. 43 © 2003 SGC Inc
5.1.3 VSWR Detector
A directional coupler is formed from current transformer T2 and
voltage transformer T1, with termination resistors R33, R34, R35,
and R36. The coupler is inserted in the 50-ohm transmission line
between the input connector, ST2 RF - ST3 GND, and the tuning
network. Forward power is measured across R33, R34 and
reflected power is measured across R35, R36. Diode D1 generates
a positive DC voltage proportional to forward power and D3
generates a positive DC voltage proportional to reflected power.
The forward DC output is fed to a voltage divider consisting of
R19 and R14. These voltages are input to the RF power detector
and to an A to D converter port of the processor. The reflected DC
output passes through a voltage divider consisting of R29 and R16,
and then goes to an A to D converter port of the processor.