Alc; T/R Switching And Harmonic Filter; 700/800 Mhz Rf Board - E.F. Johnson Company 5100 ES Series Service Manual

Circuit Description
5.2.3.3
To maintain the specified Transmitter output power level, Automatic Level Control (ALC)
is provided to control the drive level to the PA. The detected forward power is compared
to a reference level provided by the digital board via op amp U21A. The resulting error
voltage is applied to a power level control port of the power amplifier module. Transmitter
on/off splatter filtering is provided by an RC network (R76, R109, C267 and C141.)
5.2.3.4
The output of the power amplifier is applied to the transmit/receive RF PIN switch (D12 &
D13.) This is a high dynamic-range switch that is capable of passing the desired transmit
power with minimal compression. Any harmonics generated by the PA module and the RF
T/R switch are filtered by a harmonic filter that is between the RF T/R switch and the
antenna jack.
5.3

700/800 MHz RF Board

Note
The RF Board is not field serviceable. It must be replaced as a unit with a new board.
5-8 5100 ES Series Portable Radio Service Manual

ALC

T/R Switching and Harmonic Filter

January 2007