Motorola RADIUS GM300 Servis Kılavuzu - Sayfa 38

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Name of Manual

with the internal ÒonÓ inductance of CR2751, form a

series resonant circuit to lower the shunt impedance

presented by CR2751 when it is conducting.

In the receive mode, both diodes are off. Signals

applied at the antenna jack J1 are routed, via the har-

monic Þlter, through network L2751, C2752 and C2753

to the receiver input. In the transmit mode, 9.6T is

present and both diodes are forward-biased into con-

duction. The transmitter RF from Q2740 is routed

through CR2750, and via the harmonic Þlter to the

antenna jack. CR2751 conducts, shunting RF power

and preventing it from reaching the receiver. L2751 is

selected to appear as a 1/4 wave at the appropriate

operating frequency range so that the low impedance

of CR2751 appears as a high impedance at the junction

of CR2750 and the harmonic Þlter input.

The harmonic Þlters are seven pole low pass designs

having either a 0.1 dB ripple Chebychev response (403-

433 MHz and 438-470 MHz bands) or a Butterworth

response (465-495 and 490-520 MHz). They are charac-

terized as follows:

Range

403-433

438-470

f(-3 dB):

520 MHz

510 MHz

Loss:

0.8 dB

Front Panel Boards

The front panel housing itself contains two circuit

boards, the Display Board and the Volume/Mic Board.

There are two different types of Display Boards,

depending on model. In 2-frequency models, discrete

LEDÕs provide channel indication. In 8 or 16 frequency

models, seven-segment LED displays are used.

A third board, the Front Panel Filter Board, is located

on the front of the radio chassis.

Display Board

The 2-Frequency Display Board consists of four dis-

crete LEDÕs. Two are dual color type. They indicate

channel 1 or 2, and turn from green to red when the

radio is in the transmit mode.

The logic board provides the following control signals:

TX/BUSY (P9-1) is ßoating in RX mode, and active low

in TX mode; FPE (P9-4) supplies 5V via 10k for F2, and

0V via 10k for F1. This allows four display conditions,

as follows:

¥ F1 RECEIVE: P9-4 is low, therefore Q1003 is off

(DS1002 cannot light) and Q1001 is on (DS1001

cathodes are grounded). In receive, P9-1 ßoats,

causing DS1001 GRN to light via R1003, and

Q1002 is saturated, shorting out DS1001 RED so

it doesnÕt light.

March, 1997

465-495

490-520

620 MHz

650 MHz

0.8 dB

¥ F1 TRANSMIT: P9-4 is low, therefore Q1003 is

off (DS1002 cannot light) and Q1001 is on

(DS1001 cathodes are grounded). In transmit,

P9-1 is active low, turning off Q1002 and allow-

ing DS1001 RED to light via R1004. Also, since

P9-1 is low, DS1001 GRN is shorted out and can-

not light.

¥ F2 RECEIVE: P9-4 is high via 10k, therefore

Q1003 is saturated, grounding the cathodes of

DS1002 and turning off Q1001. Since Q1001 is

off, DS1001 cannot light. In receive, P9-1 ßoats,

causing DS1002 GRN to light via R1003, and

Q1002 is saturated, shorting out DS1002 RED so

it doesnÕt light.

¥ F2 TRANSMIT: P9-4 is high via 10k, therefore

Q1003 is saturated, grounding the cathodes of

DS1002 and turning off Q1001. Since Q1001 is

off, DS1001 cannot light. In transmit, P9-1 is

active low, turning off Q1002 and allowing

DS1002 RED to light via R1004. Also, since P9-1

is low, DS1002 GRN is shorted out and cannot

light.

DS1004 (Monitor) lights when Q1004 is satu-

rated by 5V via 10k applied to FPD (P9-3).

DS1004 (Busy) lights when Q1005 is saturated

by 5V via 10k applied to FPC (P9-6).

SW1001 (Mode) and SW1002 (Monitor) are nor-

mally-open pushbuttons which provide a low to

FPA (P9-7) and FPB (P9-5) respectively.

Display Board (8/16 Freq Models)

The 8/16 Frequency Display Board consists of three

colored indicator LEDÕs (DS1101-3), three green LEDÕs

which illuminate the keypad buttons (DS1105-7), a

dual 7-segment LED display (DS1104), a display driver

IC (U1101) and Þve momentary pushbuttons (SW1101-

5).

After power up, the microcomputer loads U1101 with

information using the SERIAL DATA (P9-10), SERIAL

CLOCK (P9-11), and DISPLAY ENABLE (P9-2) lines.

This data tells U1101 which segments and indicator

LEDÕs to illuminate. U1101 is a shift register latch. Its

outputs are active low when a particular LED is to be

illuminated, or open circuit when an LED is to remain

off. The anodes of all LED indicators or segments are

connected to the +5V DC source. The three keypad illu-

mination LEDÕs are lit at all times when +5V is present.

SW1101 through SW1105 are normally-open momen-

tary pushbuttons. When pressed, the conductive ink

on the back side of the rubber pushbutton comes in

contact with the exposed circuit pattern on the display

circuit board, providing a low resistance (less than 100

ohms) path to ground.

68 No.

Theory of Operation

Front Panel Boards

2-13