6881096C74-B May 25, 2005
Theory of Operation: Transmitter 3-35
Power Detector
The power detector consists of a main microstrip transmission line that transfers power from the
harmonic filter to the antenna and two parallel lines that are used to detect the forward and reverse
power. The forward power detection line is terminated via R5707 and R5708. RF energy coupled
onto this line is rectified and filtered via D5704 and C5715 to provide a DC voltage to the power
control circuitry that is proportional to the forward transmitted power level. The detected forward
voltage is approximately 1.5 Vdc when the radio is putting out 44 watts. Thermister R5704
compensates for temperature changes in D5704 to maintain constant DC voltage versus detected
forward power over temperature.
The reverse power detection line is terminated via R5705-06. RF energy coupled onto this line is
rectified and filtered via D5705 and C5718 to provide a DC voltage to the power control circuitry that
is proportional to the reverse power level reflected back from the antenna. Thermister R5712
compensates for temperature changes in D5705 to maintain constant DC voltage versus detected
reverse power over temperature.
3.6.2.4 Power Control (for 40W and 100W Transmitter)
The power control section is comprised of a control loop to level forward power, and protection
mechanisms to reduce power to a safe level for the given environmental conditions (see Figure 3-28
on page 3-36).
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