Driver Power Amplifier; Final Power Amplifier; Antenna Switch; Low-Pass Filter - Hytera DMR Service Manual

Service Manual

11.1.4 Driver Power Amplifier

The driver power amplifier is formed by Q804, with variable gain controlled by voltage VGG. The
maximum output power is 38.5dBm, and the maximum variable gain is 11dB.

11.1.5 Final Power Amplifier

The final power amplifier comprises Q802 and Q803, with the maximum output power of 48.5dBm, and
the maximum variable gain of 10dB. The input matching circuit is composed of C815, C839, R804, R806,
R807, R813, R818 and R861, while the power combining circuit is composed of C820, C8330, C831,
C819, C812, C841 and C842.

11.1.6 Antenna Switch

The antenna switch is used to switch between the transmitter circuit and the receiver circuit.
In TX mode, TX signal controls the switching transistor Q810, to further control the power supply 9V 3A
for the PIN diodes D801 and D802. Quiescent bias current of the PIN diode is controlled by the resistors
R821 and R825. In this mode, D801 and D802 are turned on; RF signals are applied to the low-pass
filter (composed of C871, C816, C836, C837, C838, L809, L813, and L810) and then transmitted via the
antenna port.
In RX mode, TX signal controls the switching transistor Q810, to further control the power supply for the
PIN diodes D801 and D802, which are not applied with DC bias current. When the two PIN diodes are
turned off, signals feed into the RX path through the low-pass filter (composed of L871, C852 and C862).

11.1.7 Low-pass Filter

A low-pass filter that consists of inductors L809, L813 and L810, and capacitors C836, C837, C830, is
used to attenuate harmonic energy from the transmitter.
11.1.8 Directional Coupler
A directional coupler that consists of microstrip directional coupler, D803, D804 and etc, is used to detect
both forward and reverse directed power of the transmitter. The forward power is coupled to the diode
D803, and the voltage is applied to the power control circuit (U801). Then the voltage VGG is output to
control the gate voltage of pre-driver and driver PA, ensuring a constant power output.
The directional coupler can adjust the TX power and detect the VSWR load. The reverse power is
coupled to D804. The voltage is applied to U802 and then feeds into U302 for detection
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