- ページ 12

ラジオ Motorola CP040のPDF サービス情報をオンラインで閲覧またはダウンロードできます。Motorola CP040 48 ページ。 Commercial radios uhf1
Motorola CP040 にも：詳細サービスマニュアル (28 ページ), サービス情報 (46 ページ), ユーザーマニュアル (18 ページ), サービス情報 (30 ページ)

ページを印刷する

2-4

3.0

VHF Transmitter

The VHF transmitter covers the range of 136-162 MHz. Depending on model, the output power of

the transmitter is either switchable on a per-channel basis between high power (5 watts) and low

power (1 watt), or is factory preset to 2 watts. The transmitter is divided into four major blocks as

shown in Figure 2-2.

■

Power Amplifier

■

Harmonic Filter

■

Antenna Matching Network

■

Power Control.

TX_ENA

PWR_SET

TX_INJ

Q100

(From VCO)

3.1

Transmitter Power Amplifier

The transmitter power amplifier has three stages of amplification. The first stage, Q100, operates in

Class AB from the 5T source. It provides 13 dB of gain and an output of 20 mW. The current drain is

typically 25mA. Components C105-C107 and L103 match the output of Q100 to the 50Ω input of the

module U110.

U110 is a two stage Silicon MOS FET power amplifier module. Drain voltage is obtained from

UNSW B+ after being routed through current-sense resistor R150 in the power control circuit. The

output power of the module is controlled by varying the DC gate bias on U110 pin 2 (VGG).

3.2

Antenna Switch

The antenna switch consists of two pin diodes, D120 and D121. In the receive mode, both diodes

are off. Signals applied at the antenna or at jack J140 are routed, via the harmonic filter, through

network C122-C124 and L121, to the receiver input. In the transmit mode, Q170 is on and TXB+ is

present, forward-biasing both diodes into conduction. The diode current is 50 mA, set by R120-

R122. The transmitter RF from U110 is routed through D120, and via the harmonic filter to the

antenna jack. D121 conducts, shunting RF power and preventing it from reaching the receiver. L121

is selected to appear as a 1/4 wave at VHF, so that the low impedance of D121 appears as a high

impedance at the junction of D120 and the harmonic filter input. This provides a high series

impedance and low shunt impedance divider between the power amplifier output and receiver input.

USWB+

Power Control

VGG

VDD

Power Amplifier Module U110

RX_IN

(To Receiver)

Figure 2-2 VHF Transmitter Block Diagram

Harmonic Filter

Antenna

Switch

Antenna

Matching

Network

THEORY OF OPERATION

J140 Antenna

Jack

Antenna