MFJ MFJ-902 - User Manual

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MFJ-902/902H Travel Tuner Instruction Manual

INTRODUCTION

The MFJ-902/902H Travel Antenna Tuner was specially compact-built for Icom

IC-706MKIIG, Yaesu FT-100, Kenwood TS-50, and other rigs with a built-in

SWR Meter.

You can operate 80 through 10 Meters -- anywhere with any transceiver -- use

any coax fed or random wire antenna. The 902H also has a 4:1 balun with

binding post for balanced lines. It’s great for mobile, base, backpack, etc. The

MFJ-902/902H handles 150 watts RF output and has a tuner bypass switch.

INSTALLATION

The MFJ-902/902H should be installed between the transmitter and antenna.

1. Locate the tuner in a convenient location at the operating position.

2. Use a 50 ohm coaxial cable to connect the transmitter or transceiver to the

SO-239 labeled TRANSMITTER on the back of the tuner.

3. Connect an antenna feed to the appropriate tuner output:

a.) COAX-FEED to the SO-239 connector labeled ANTENNA.

b.) RANDOM WIRE

MFJ-902: A random wire may be used by connecting to the center of

the SO-239 connector with the supplied plug.

MFJ-902H: Connect to the red binding post labeled WIRE.

The MFJ-902/902H must be grounded when using a random wire.

c.) BALANCED FEEDERS (MFJ-902H only) to the red binding posts

labeled BALANCED LINE. When using a balanced feedline, connect a

short jumper from the WIRE binding post to the closest balanced line

post (see labeling on back of unit).

4. Connect your tuner and transmitter to a good earth ground.

OPERATION

This tuner has a BYPASS/TUNE switch located on the back of the unit. Simply

place the switch toward the BYPASS labeling to completely bypass the tuning

circuit. Change the switch toward the TUNE labeling to place the tuning circuit

between the transmitter/transceiver and the antenna.

Need help?

Do you have a question about the MFJ MFJ-902 and is the answer not in the manual?

Summary

Introduction to MFJ-902;902 H Travel Tuner

Installation Guide

Locate the Tuner

Position the tuner in a convenient location at the operating position.

Connect Transmitter

Use a 50 ohm coaxial cable to connect the transmitter or transceiver to the tuner.

Connect Antenna Feed

Connect an antenna feed to the appropriate tuner output: COAX-FEED, RANDOM WIRE, or BALANCED LINE.

Grounding

Connect your tuner and transmitter to a good earth ground.

Operation and Tuning

BYPASS;TUNE Switch

Locate the BYPASS/TUNE switch on the back of the unit to engage or bypass the tuning circuit.

Tuning Procedure

Step-by-step instructions for adjusting controls to achieve the lowest reflected power (best SWR).

Summary

Introduction to MFJ-902;902 H Travel Tuner

Installation Guide

Locate the Tuner

Position the tuner in a convenient location at the operating position.

Connect Transmitter

Use a 50 ohm coaxial cable to connect the transmitter or transceiver to the tuner.

Connect Antenna Feed

Connect an antenna feed to the appropriate tuner output: COAX-FEED, RANDOM WIRE, or BALANCED LINE.

Grounding

Connect your tuner and transmitter to a good earth ground.

Operation and Tuning

BYPASS;TUNE Switch

Locate the BYPASS/TUNE switch on the back of the unit to engage or bypass the tuning circuit.

Tuning Procedure

Step-by-step instructions for adjusting controls to achieve the lowest reflected power (best SWR).

The MFJ-902/902H Travel Antenna Tuner is a compact device designed to match transmitters to various antenna types, particularly for Icom IC-706MKIIG, Yaesu FT-100, Kenwood TS-50, and other rigs with a built-in SWR Meter. It allows operation across the 80 through 10 Meter bands.

Function Description:

The primary function of this tuner is to provide impedance matching between a transmitter/transceiver and an antenna system to achieve a low Standing Wave Ratio (SWR). This ensures maximum power transfer from the transmitter to the antenna and protects the transmitter from high SWR conditions. It supports multiple antenna configurations, including coax-fed antennas, random wire antennas, and balanced line antennas (MFJ-902H only). The device includes a BYPASS/TUNE switch, allowing the user to either engage the tuning circuit or bypass it completely.

Important Technical Specifications:

Frequency Coverage: 80 through 10 Meters. It is explicitly stated not to operate on 160 Meters.
Power Handling: The tuner can handle up to 150 watts RF output. Exceeding this limit will damage the tuner.
Antenna Connections:
- Coax-fed: Connects to the SO-239 connector labeled ANTENNA.
- Random Wire: For MFJ-902, connect to the center of the SO-239 connector with the supplied plug. For MFJ-902H, connect to the red binding post labeled WIRE.
- Balanced Feeders (MFJ-902H only): Connects to the red binding posts labeled BALANCED LINE. A short jumper is required from the WIRE binding post to the closest balanced line post when using a balanced feedline.
Balun: The MFJ-902H model includes a 4:1 balun for balanced lines.
Controls:
- TRANSMITTER control: A variable capacitor for matching, with maximum capacitance at position 0 (fully meshed) and minimum at position 10 (fully open).
- ANTENNA control: A variable capacitor for matching, with maximum capacitance at position 0 (fully meshed) and minimum at position 10 (fully open).
- INDUCTANCE switch: Provides varying levels of inductance, with maximum inductance at position "A" and minimum at position "L".
- BYPASS/TUNE switch: Located on the back, it toggles between bypassing the tuning circuit and engaging it.

Usage Features:

Installation: The tuner should be installed between the transmitter and the antenna. It requires a 50 ohm coaxial cable to connect the transmitter to the SO-239 labeled TRANSMITTER.
Grounding: The MFJ-902/902H must be grounded when using a random wire. A good earth ground is recommended for both the tuner and transmitter.
Tuning Procedure:
1. Set TRANSMITTER control to 5 and ANTENNA control to 0.
2. Place BYPASS/TUNE switch in TUNE position.
3. Apply low power to obtain a noticeable deflection on the reflected power or SWR meter.
4. Adjust the INDUCTOR control for the lowest reflected power.
5. Carefully adjust TRANSMITTER and ANTENNA controls iteratively: adjust TRANSMITTER for lowest reflected power, then slightly increase ANTENNA and readjust TRANSMITTER for lowest reflected power. Repeat until the lowest reflected power (best SWR) is achieved.
6. After achieving the lowest reflected power, use the INDUCTOR switch to reduce inductance one position (towards L). Readjust TRANSMITTER and ANTENNA for the lowest SWR. Continue this process until the lowest SWR cannot be repeated, then increase the INDUCTOR switch by one position (towards A). Tune for the lowest SWR.
Important Tuning Notes:
- Always use the highest possible capacitance for TRANSMITTER and ANTENNA controls for smoother tuning, higher efficiency, and greater power handling.
- Always use the minimum amount of inductance possible. Minimum inductance provides the best efficiency, maximum power handling, and widest bandwidth.
- Never transmit while changing the INDUCTOR switch.
- The controls (TRANSMITTER, ANTENNA, INDUCTOR) interact, requiring iterative adjustments.
Power Increase: Once a low SWR is obtained, the transmitter power can be increased up to 150 watts.

Maintenance Features:

Technical Assistance: For problems not resolved by the manual, users can contact MFJ Technical Service at 662-323-0549 or the MFJ Factory at 662-323-5869. When calling, have the unit, manual, and station information ready.
Written/Email Support: Questions can also be sent by mail to MFJ Enterprises, Inc., 300 Industrial Park Road, Starkville, MS 39759; by Facsimile to 662-323-6551; or by email to techinfo@mfjenterprises.com. A complete description of the problem, unit usage, and station setup should be included.