Kenwood TR-7400A 2m FM Transceiver Operating Manual

Introduction

This document is the operating manual for the Kenwood TR-7400A, a 2-meter FM transceiver. It provides detailed information on the controls, installation, operation, specifications, and internal circuitry of the device.

Table of Contents

• SECTION 2. CONTROLS AND WHAT THEY DO
  • 2.1 Front Panel
  • 2.2 Rear Panel
  • 2.3 Side Panel
• SECTION 3 GENERAL TIPS ON INSTALLATION
  • 3.1 Mobile Use
  • 3.2 Fixed-Station Use
• SECTION 4 OPERATION
  • 4.1 Receiving
  • 4.2 Transmitting
  • 4.3 How to Use the TX Offset Switch
  • 4.4 How to Use the Hi/Low Selector Switch
  • 4.5 How to Use the Tone Selector Switch
  • 4.6 Description of "Unlock" Indicator
  • 4.7 How to Use the Tone Pad
• SECTION 5 ADDITIONAL INFORMATION
  • BLOCK DIAGRAM
  • TOP & BOTTOM VIEW OF THE TR-7400A
  • SCHEMATIC DIAGRAM

SECTION 2. CONTROLS AND WHAT THEY DO

2.1 Front Panel

The front panel of the TR-7400A features numerous controls for operation. A diagram (Fig. 1) illustrates their locations.

• 1. POWER Switch: Used to turn the transceiver ON or OFF.
• 2. ON/OFF Indicator: Illuminates when the POWER Switch (1) is ON.
• 3. TONE Selector Switch: Selects between TONE mode and SUB mode.
• 4. TX OFFSET Switch: Sets the transmit frequency offset for repeater operation (+600 or -600 kHz).
• 5. Meter: Displays signal strength during receive and RF output power during transmit.
• 6. ON AIR Indicator: Lights up when the unit is in transmit mode.
• 7. 5 kHz Offset Switch: Selects 5 kHz offset.
• 8. Digital Frequency Display: Shows the current operating frequency in 6 digits.
• 9. SQU Control (Outer ring): Adjusts the squelch threshold to eliminate background noise.
• 10. VOL Control (Inner knob): Adjusts the audio output volume.
• 11. MIC Connector: A standard 4-pin connector for the microphone.
• 12. MHz Selector Switch: Selects the primary MHz band (e.g., 144, 145, 146, 147 MHz).
• 13. 100 kHz Selector Switch: Selects channels in 100 kHz increments.
• 14. 10 kHz Selector Switch: Selects channels in 10 kHz increments.
• 15. TX OFFSET Switch: (This appears to be a duplicate label for switch 4 or 17 in the diagram. The diagram labels the switch as 17).
• 16. Unlock Indicator: Indicates the status of the Phase-Locked Loop (PLL).
• 17. TX OFFSET Switch: Sets the transmit frequency offset to +600 or -600.

2.2 Rear Panel

Details for the rear panel are not extensively covered in the provided OCR text.

2.3 Side Panel

The side panel features connectors for external devices.

• 21. EXT SP Connector: For connecting an external 8-ohm speaker.
• 22. TONE PAD Connector: A 600-ohm input for connecting a tone pad for "Auto-patch" operation.
• 23. Mounting Rail: Used to attach the transceiver to a mounting bracket.
• 24. Snap Lock: Secures the transceiver body to the mounting bracket.
• 25. Stand-off: Attachable supports to provide a convenient viewing angle.

SECTION 3 GENERAL TIPS ON INSTALLATION

This section provides guidance for installing the TR-7400A.

3.1 Mobile Use

For mobile installations, ensure secure mounting and proper power connections. The unit requires a DC power supply with 8 to 10A capacity at 13.8V.

3.2 Fixed-Station Use

For fixed-station use, similar considerations apply regarding power and antenna connections. The diagram (Fig. 5) illustrates the mounting bracket installation process, including attaching the bracket to the body with bolts and washers, sliding the unit into the bracket, and securing it with a pawl and lock mechanism. It also shows how to adjust the vertical angle of the set.

SECTION 4 OPERATION

4.1 Receiving

1. Connect the supplied power cable to the DC power connector (18) and the antenna cable to the ANT connector (20). Use a DC power supply or battery pack with 8 to 10A current capacity at 13.8V. CAUTION: Ensure correct polarity for power cable leads.
2. Depress the POWER ON Switch (1). The Digital Frequency Display (8) will show the frequency, and the meter (5) will illuminate.
3. Set the TONE Selector Switch (3) to OFF.
4. Turn the SQU Control (9) fully counterclockwise.
5. Turn the VOL Control (10) clockwise until noise is audible at a comfortable level.
6. Set the MHz (12), 100 kHz (13), and 10 kHz (14) Selector Switches, and the 5 kHz Offset Switch (15) to the desired receive frequency. If a signal is received, the Meter (5) will indicate its strength.
7. To eliminate noise with no input signal, gradually turn the SQU Control (9) clockwise until the noise threshold is reached.

NOTE: The Unlock Indicator (16) may light momentarily during operation, which is normal.

4.2 Transmitting

1. Plug the supplied microphone cable into the MIC Connector (11).
2. Set the TONE Selector Switch (3) to OFF.
3. Set the TX OFFSET Switch (17) to SIMP (This likely refers to the SIMP position shown on the switch, not a mode).
4. Set the MHz (12), 100 kHz (13), and 10 kHz (14) Selector Switches, and the 5 kHz Offset Switch (15) to the desired transmit channel.
5. Depress the microphone push-to-talk switch to transmit. The ON AIR Indicator (6) will light, and the Meter (5) pointer will indicate RF output power.
6. Maintain a distance of 5 to 10 cm between your mouth and the microphone.

4.3 How to Use the TX Offset Switch

The TX OFFSET Switch (17) is used to select the transmit frequency offset for repeater operation. It can be set to +600 or -600 kHz. The green indicator shows -600, and the red indicator shows +600.

4.4 How to Use the Hi/Low Selector Switch

This switch likely controls the transmit power level (High/Low), though not explicitly detailed in the OCR.

4.5 How to Use the Tone Selector Switch

The TONE Selector Switch (3) controls the tone squelch and tone burst functions. Setting it to OFF disables these features.

4.6 Description of "Unlock" Indicator

The Unlock Indicator (16) on the front panel lights red when the protection circuit operates, stopping local oscillator and thus shutting down receive and transmit. However, the PLL may work normally even if the Unlock Indicator (16) lights momentarily in the following cases:

• When the POWER ON Switch (1) is depressed and released.
• When the MHz (12), 100 kHz (13), and 10 kHz (14) Selector Switches are turned, or the 5 kHz Offset Switch (15) is depressed.
• When the microphone button is depressed or released while the TX OFFSET Switch (17) is at +600 or -600 for repeater operation.
• When the TX OFFSET Switch (17) is shifted to +600 or -600 during transmit.

4.7 How to Use the Tone Pad

The TR-7400A includes a tone pad input for "Auto-patch" operation. To use this feature, connect a tone pad available on the market using the supplied miniature plug. The diagram (Fig. 12) shows the TONE PAD Connector and the connection of a touch tone pad.

SECTION 5 ADDITIONAL INFORMATION

BLOCK DIAGRAM

The block diagram (Fig. 14) illustrates the main functional units of the TR-7400A and their interconnections. Key units include:

• RX UNIT (X55-1150-10): Handles receiving functions, including RF amplification, mixing, IF processing, and demodulation.
• VCO UNIT (X50-1370-10): Contains the Voltage-Controlled Oscillator, crucial for frequency generation.
• SWITCH BOARD: Manages various switching functions, including TX OFFSET and CHANNEL SELECTOR.
• PD UNIT (X50-1380-10): Likely a Phase Detector or Power Distribution unit.
• TX UNIT (X56-1230-10): Manages transmitting functions, including modulation, power amplification, and tone burst generation.
• DISPLAY UNIT (X54-1210-10): Controls the digital frequency display.
• PLL (Phase-Locked Loop): A control system for frequency stability.

The diagram shows signal paths between these units, including inputs for MIC and external power (DC 13.8V), and outputs for external speaker (EXT SP).

TOP & BOTTOM VIEW OF THE TR-7400A

An internal view (Page 17) shows the layout of major circuit boards and components. The main sections visible are the SWITCH BOARD, VCO UNIT, and RX UNIT. The TONE UNIT (optional) is also indicated. Various adjustment points are labeled, such as S meter ADJ., Tone dev. ADJ., Protection ADJ., and Herical resonator.

SCHEMATIC DIAGRAM

The schematic diagram (Fig. 15-16) provides a detailed circuit layout. It shows the intricate connections of components within each functional unit. Key areas include the RF and IF stages of the receiver, the transmitter stages including power amplification, the frequency synthesis circuitry involving PLL and VCO, and the control logic for channel selection and offsets. Component lists for diodes, transistors, and modules are provided, detailing their types and part numbers (e.g., 2SC460, 2SC1000, 1N60, TA7061AP, MRF208, TBM modules).

Technical Specifications

Tone Burst Oscillator Module List

NOTE: The circuit and ratings may change without notice due to development in technology.

Manufacturer Information

A product of TRIO-KENWOOD CORPORATION, 6-17. 3-chome. Aobadai, Meguro-ku, Tokyo 153, Japan. © 8473 PRINTED in JAPAN B50-2515-00 (T)