Galaxy dx979 Service Manual

Model DX 979



CB Radio

Service Manual

TABLE OF

DX 979

CONTENTS

PAGE

CHAPTER 1

SPECIFICATIONS

1.0 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.1 Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2 Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

CHAPTER 2

OPERATION

2.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.1 Control & Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

2.2 Microphone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . … 7

2.3 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . … 7

2.4 Alternate Microphones And Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

CHAPTER 3

CIRCUIT DESCRIPTION

3.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.1 PLL Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 9

3.2 Receiver Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.3 Transmitter Modulation Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . … 9

3.4 Transmitter Amplifier Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

CHAPTER 4

ALIGNMENT

4.0 Required Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . … 11

4.1 Alignment Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

CHAPTER 5

MAINTENANCE

5.0 Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

5.1 Periodic Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 16

5.2 Fuse Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

CHAPTER 6

DIAGRAMS AND PARTS LIST

6.0 PCB Layout & Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

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DX 979

1.0 GENERAL

Model DX 979 Channels 40 Frequency Range 26.965 – 27.405 MHz Emission Modes AM/USB/LSB Frequency Control Phase Lock Loop (PLL) synthesizer Frequency Tolerance 0.005 % Frequency Stability 0.001 % Operating Temperature Range Microphone Input Voltage 13.8V DC Antenna Connector UHF; SO239 Dimensions 7 1/4”(W) x 9”(D) x 2 1/4”(H) Weight 3.5 lbs.

1.1 TRANSMITTER

RF Power Output AM: 4W; USB/LSB: 12W PEP RF Transmit Modes AM/SSB Modulation High and Low level Class B, Amplitude Modulation:

Spurious Emissions - 60dB Carrier Suppression - 60dB Audio Frequency Response 300 to 2500 Hz Antenna Impedance 50 Ohms Output Indicators Meter shows incoming signal strength, RF output

1.2 RECEIVER

Sensitivity For 10dB S/N (AM/ SSB) AM: < 0.5 uV ; USB/LSB: < 0.25 uV IF Frequency AM: 10.695 MHz 1st IF, 455 KHz 2nd IF Image Rejection - 50dB Adjacent Channel Selectivity - 60dB RF Gain Control 45dB adjustable for optimum signal reception Automatic Gain Control (AGC) Figure Of Merit 100mV for 10dB Change in Audio Output Squelch Noise Blanker RF type Audio Output Power 2.5W @ 10% THD Audio Frequency Response 300 to 2500 Hz Built-in Speaker 8 Ohms, 4 Watts External Speaker (Not Supplied) 8 Ohms, 4 Watts

(SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE)

CHAPTER 1

SPECIFICATIONS

-30°C to +50°C Dynamic PTT, 500 Ω

AM and SSB.

power, SWR and AM Modulation level. Transmit LED glows red when transmitter is in operation.

Adjustable; threshold less than 0.5µV

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CHAPTER 2

DX 979

MOD

PWR

SWR

DX 979

11 1413 1815

TALKBACK

OFF

CLARIFIER

VOL SQ

OFF

SWR

PWR

CBMOD

NB/ANL

OPERATION

16 17

USB

RX/TX

SWR

LSB

DIM PWRMIC RF

1 23 5476

Figure 2-1 Front Panel

2.0 INTRODUCTION

This section explains the basic operating procedures for the DX 979 mobile CB radio.

2.1 CONTROLS AND CONNECTIONS

2.1.1 FRONT PANEL

Refer to the above Figure 2-1 for the location of the following controls.

1. MICROPHONE JACK: Used to connect microphone for voice source.

2. SQUELCH CONTROL: This knob is used to eliminate background noise being heard through the

receiver, which can be disturbing when no transmissions are being heard through the receiver. To use this feature, turn the knob fully counterclockwise and then turn clockwise slowly until the background noise is just eliminated. Further clockwise rotation will increase the threshold level which a signal must overcome in order to be heard. Only strong signals will be heard at a maximum clockwise setting.

3. ON/OFF VOLUME CONTROL: This knob controls the volume and power to the radio. To turn

radio on, rotate the knob clockwise. Turning the knob further will increase the volume of the receiver.

4. RF GAIN CONTROL: This control is used to reduce the gain of the RF (receive) amplifier under

strong signal conditions.

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5. MIC GAIN CONTROL: Adjusts the microphone gain in the transmit and PA modes. This

controls the gain to the extent that full talk power is available several inches away from the microphone. In the Public Address (PA) mode, the control functions as the volume control.

6. RF POWER CONTROL: This control allows the user to adjust RF power output.

7. DIMMER CONTROL: This knob controls the level of brightness for the faceplate lettering, meter

lamp and channel display.

8. SWR LED: This LED lights red when your SWR is higher than about 3:1. This is not an exact

indicator of 3:1 SWR, but it is an indication that you should check your SWR reading.

9. CHANNEL SELECTOR: This control is used to select the desired transmit and receive channel.

10. FRONT PANEL METER: The front panel meter allows the user to monitor incoming signal

strength, RF output power, SWR level and AM modulation level.

11. ILLUMINATED FACE PLATE: All faceplate lettering will fully illuminate to allow the user

easy viewing at night. This unique, solid state, backlight is designed to maximize night vision while minimizing eye fatigue. Therefore, it is ideal for switch and control recognition day or night.

12. TALKBACK CONTROL: Adjust this knob for desired volume of Talkback. This is used to

monitor your own voice. For example, you could use this feature to compare different microphones.

13. CLARIFIER CONTROL: Allows tuning of the receive frequency above or below the channel

frequency by up to 1.0KHz. Although this control is intended primarily to tune in SSB signals, it may be used to optimize AM signals.

14. SWR/MOD/PWR SWITCH: This switch controls the function of the meter during the transmit

mode. In the “SWR” position, the meter indicates the Standing Wave Ratio (SWR) of your antenna. There are no adjustments because the SWR circuit in this radio calibrates itself automatically. When the switch is in the “MOD” position, the green scale on the meter indicates your percentage of modulation in the AM mode only. They are most accurate when testing at maximum power output. When this switch is in “PWR” position, the meter indicates your power output.

15. NB-ANL/CB/PA SWITCH: When the switch is in the NB/ANL position, the Noise Blanker (NB)

and Automatic Noise Limiter (ANL) circuits are activated. The Noise Blanker is very effective in eliminating repetitive impulse noise such as ignition interference. In the CB position, the PA function is disabled and the radio will transmit and receive on the speaker that is connected. In the PA position, the radio acts as public address amplifier. Your voice will come out of the speaker that is plugged into the PA. SP. jack on the rear panel. The radio does not operate when you are in the PA mode.

16. MODE SWITCH: This control allows you to select one of the following operating modes:

AM/USB/LSB.

17. RX/TX LED: This LED is green during receive and red during transmit.

18. CHANNEL DISPLAY: The channel display indicates the current selected channel.

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REAR PANEL

Figure 2-2 represents the location of the following connections:

3 45

This device complies with part 15 of the FCC Rules. Operation is subject to the condit ion that this device does not cause harmful interference.

Servic e Manual at www.GalaxyRadios.com

MODEL NO. : DX 979

AM/SSB 40 CH

CB TRANSCEIVER

DATE OF MFG.:

FCC ID : MEE − DX − 979

SERIAL NO. :

PA SP.

ANT

- DC 13.8V +

EXT SP.

F.C.

Figure 2-2 Rear Panel

1. ANTENNA: This jack accepts a 50 ohm coaxial cable with a PL-259 type plug.

2. DC POWER: This jack accepts the 13.8V DC power cable with built-in fuse. The power cord

provided with the radio has a black and red wire. The black goes to negative and red goes to positive.

3. PA SP: This jack is for PA operation. Before operating, you must first connect a PA speaker (8

ohms, 4W) to this jack.

4. EXT. SP: This jack accepts a 4 to 8 ohm, 5 watt external speaker. When the external speaker is

connected to this jack, the built-in speaker will be disabled.

5. F.C.: This jack is used to connect the optional Galaxy FC347 six-digit frequency counter. All

connections, including DC power, are provided to the FC347 through this jack.

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2.1.3 FREQUENCY CHART

CHANNEL

CHANNEL FREQUENCY

(MHz)

CHANNEL

CHANNEL FREQUENCY

(MHz)

1 26.965 21 27.215 2 26.975 22 27.225 3 26.985 23 27.255 4 27.005 24 27.235 5 27.015 25 27.245

6 27.025 26 27.265 7 27.035 27 27.275 8 27.055 28 27.285 9 27.065 29 27.295

10 27.075 30 27.305 11 27.085 31 27.315

12 27.105 32 27.325 13 27.115 33 27.335 14 27.125 34 27.345 15 27.135 35 27.355

16 27.155 36 27.365 17 27.165 37 27.375 18 27.175 38 27.385 19 27.185 39 27.395 20 27.205 40 27.405

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2.2 MICROPHONE

The receiver and transmitter are controlled by the push-to-talk switch on the microphone. Press the switch and the transmitter is activated, release the switch to receive. When transmitting, hold the microphone two inches from your mouth and speak clearly in a normal voice. The radio comes complete with a low impedance (500 ohm) dynamic microphone.

2.3 OPERATION

2.3.1 PROCEDURE TO RECEIVE

1. Be sure that the power source, microphone and antenna are connected to the proper connectors before going to the next step.

2. Press the POWER switch to apply power to the radio.

3. Set the VOL to a comfortable listening level.

4. Set the MODE switch to the desired mode.

5. Listen to the background noise from the speaker. Turn the SQUELCH knob slowly clockwise until the noise just disappears. The SQUELCH is now properly adjusted. The receiver will remain quiet until a signal is actually received. Do not advance the control too far or some of weaker signals will not be heard.

6. Set the CHANNEL selector switch to the desired channel.

7. Set the RF GAIN control fully clockwise for maximum RF gain.

8. Adjust the CLARIFIER control to clarify the SSB signals or to optimize AM signals.

2.3.2 PROCEDURE TO TRANSMIT

1. Select the desired channel of transmission

2. Set the MIC GAIN control fully clockwise.

3. If the channel is clear, depress the push-to-talk switch on the microphone and speak in a normal voice.

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2.4 ALTERNATE MICROPHONES AND INSTALLATION

For best results, the user should select a low impedance dynamic type microphone or a transistorized microphone. Transistorized type microphones have a low output impedance characteristic. The microphones must be provided with a four-lead cable. The audio conductor and its shielded lead comprise two of the leads. The third lead is for transmit control and the fourth is for receiving control.

The microphone should provide the functions shown in the schematic below (Figure 2-3).

4 WIRE MIC CABLE

Pin Number Mic Cable Lead

1 Audio Shield 2 Audio Lead 3 Transmit Control 4 Receive Control

Figure 2-3 Your Transceiver Microphone Schematic

Figure 2-4 Microphone plug and pin numbers viewed from rear of pin receptacle.

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DX 979

3.0 INTRODUCTION

This section explains the technical theory of operation for the DX 979 mobile CB radio.

3.1 PLL CIRCUIT

The Phase Lock Loop (PLL) circuit is responsible for developing the receiver’s first local oscillator signal and the transmitter’s exciter signal. The PLL circuit consists primarily of IC2, IC3, Q25, Q29 and Q28. The PLL circuit is programmed by the rotary channel switch GPS-668. The GPS-668 communicates the correct binary data information to the programmable divider inside of IC3. IC3 then controls the VCO (Voltage Controlled Oscillator) to oscillate on the correct frequency. This signal is fed either into the receiver’s first mixer (for receive operation) or the transmitter’s mixer (for transmit operation).

3.2 RECEIVER CIRCUIT

The incoming RF signal comes into the radio via the antenna and into the front-end pre-amp, Q17. The RF signal is fed into the mixer circuit of Q18/Q19 and then into the AM IF section of the receiver. The signal is then detected by the AM detector and then fed to the audio amplifier section of the receiver and finally out to the speaker.

3.3 TRANSMITTER MODULATION CIRCUIT

(1) The transmitter modulation circuit modulates the low-level RF signal from the PLL exciter circuit

with the user’s audio voice signal from the microphone. The audio from the microphone is then amplified and fed into the transmit amplifier circuit.

(2) If the transceiver is in the AM mode, the AF power amplifier modulates the last RF amplifier,

which produces a true amplitude modulated RF signal.

(3) If the transceiver is in the SSB mode, the audio signal is mixed with the 10.6975MHz oscillator in

IC6.

3.4 TRANSMITTER AMPLIFIER CIRCUIT

The transmitter takes the basic exciter signal from IC9 of the TX mixer and amplifies it through a series of amplifiers consisting of Q52, Q51, Q49 and Q47 where it is sent out to the antenna connector.

CHAPTER 3

CIRCUIT

DESCRIPTION

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- 10 -

DX 979

CHAPTER 4

ALIGNMENT

4.0 REQUIRED TEST EQUIPMENT

c DC Power Supply (13.8VDC, 10A) d RF Wattmeter (10W) e Multi-meter f Automatic Modulation Meter g Audio Signal Generator

h Frequency Counter (100 MHz) i RF Signal Generator (100 MHz) j Automatic Distortion Meter k Oscilloscope (50 MHz) l Sinad Meter

4.1 ALIGNMENT PROCEDURES

This transceiver has been aligned at the factory and does not require any adjustments at installation. The required test equipment listed are used for the test setup or alignment shown in Figure 4-1 Transmitter Test Setup and Figure 4-2 Receiver Test Setup. These test setups are used in part or total during the following adjustments. Refer to page 15 for adjustment locations.

4.1.1 PLL ALIGNMENT

ITEM U.U.T. SETTING

VCO Disconnect ‘short PCB’ from TP7, TP8 and TP9.

Set radio to CH 1 AM RX mode. Connect Multi-meter to TP2.

Set CLARIFIER Control to 12 o’clock.

Connect Frequency Counter to IC3 Pin 8. VC1 AM

Frequency USB

Frequency LSB

Frequency TX Offset

Frequency

Connect Oscilloscope to TP3.

Set radio to CH 19 AM RX mode. Connect Frequency Counter to TP3.

Set radio to CH 19 USB RX mode. Connect Frequency Counter to TP3.

Set radio to CH 19 LSB RX mode. Connect Frequency Counter to TP3.

Set radio to CH 19 LSB TX mode. Connect Frequency Counter to TP3.

AM OSC Set radio to CH 19 AM TX mode.

Connect Frequency Counter to TP5.

USB OSC Set radio to CH 19 USB TX mode.

Connect Frequency Counter to TP5. Set VR6 fully clockwise

LSB OSC Set radio to CH 19 LSB TX mode.Connect

Frequency Counter to TP5. Set VR6 back to mid position when finished.

ADJUST

POINT

L14

L15

L20

L21

L22

VR7

L23

L24

L25

MEASUREMENT

2.5 VDC ± 0.1

Adjust for max.

10.2400MHz ± 20Hz

16.4900MHz ± 20Hz

16.4925MHz ± 20Hz

16.4875MHz ± 20Hz

10.6950MHz ± 10Hz

10.6925MHz ± 10Hz

10.6975MHz ± 10Hz

- 11 -

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Galaxy dx979 Service Manual

Specifications and Main Features

Frequently Asked Questions

User Manual