MFJ MFJ-204B User Manual

MFJ Antenna Bridge

Model MFJ-204B

INSTRUCTION MANUAL

VERSION 0B

CAUTION: Read All Instructions Before Operating Equipment

MFJ ENTERPRISES, INC.

300 Industrial Park Road

Starkville, MS 39759 USA

Tel: [phone] Fax: [phone]

COPYRIGHT 2006 MFJ ENTERPRISES, INC.

C

MFJ-204B Instruction Manual MFJ Antenna Bridge

DISCLAIMER

Information in this manual is designed for user purposes only and is not intended to supersede information
contained in customer regulations, technical manuals/documents, positional handbooks, or other official
publications. The copy of this manual provided to the customer will not be updated to reflect current data.

Customers using this manual should report errors or omissions, recommendations for improvements, or other
comments to MFJ Enterprises, 300 Industrial Park Road, Starkville, MS 39759. Phone: [phone]; FAX:
[phone]. Business hours: M-F 8-4:30 CST.

MFJ-204B Instruction Manual MFJ Antenna Bridge

Table of Contents

TOPIC

PAGE

1. TABLE OF CONTENTS 2

2. LIST OF FIGURES AND TABLES 2

3. INTRODUCTION AND FEATURES 3

4. USES FOR THE MFJ-204B 4

5. SYSTEM CONTROLS AND INDICATORS 5

6. THEORY OF OPERATION 7

7. MFJ-204B EASY-START INSTRUCTIONS 8

8. IN CASE OF DIFFICULTY 13

9. TECHNICAL ASSISTANCE 13
APPENDICES
A. Zero Beating Against a Receiver 12
LIST OF FIGURES
Figure 1 Front Panel Jacks and Controls 5
Figure 2 End Panel Jacks 6
Figure 3 Block Diagram 7
Figure 4 MFJ-204B to Tuner Hook Up

9

Figure 5 Schematic Diagram 11

MFJ-204B Instruction Manual MFJ Antenna Bridge

INTRODUCTION:

The MFJ-204B gives you a direct readout of your antenna’s SWR without the need for formulas or indirect
readings. The MFJ-204B can also be used to adjust a tuner to match your antenna without the need for
transmitting. The frequency coverage for the MFJ-204B is from below 1.75 MHZ to Above 30 MHZ in 5 user
selectable bands.

FEATURES
Portable – The MFJ-204B’s light weight, small size and internal battery capability makes it great f o r Field

Day, Travel or any time you need to check out a new antenna installation quickly easily.

Great Value – The MFJ-204B’s low cost puts a great instrument in your hands for those who only need to
adjust their antennas occasionally.

Stable – With built in AGC the MFJ-204B is accurate across the bands. No false readings.

Wide Range – Determine the RF Resistance of your antenna from 10 to over 600 ohms.

Rugged Construction: Attractive all-metal cabinet, conservative component selection and extensive RF

filtering ensure solid performance for years to come. Fully covered by MFJ’s “No Matter What” one year
limited warranty.

Before attempting to operate your MFJ-204B, please read the manual thoroughly. It contains important detail
about setting up your unit to obtain the best performance.

USES

Your MFJ-204B ANTENNA BRIDGE has many uses. It can be used to find the resonant frequency of your
antenna, to find the SWR of your antenna at a particular frequency, and to find the frequency at which your
antenna has the lowest SWR. You can also use the Antenna Bridge to adjust your antenna to a low SWR and to
adjust an antenna tuner to match the transmitter to your transmission line. You can even find out if your
antenna is resonant on more that one frequency.

The added benefit of using an Antenna Bridge over a SWR meter is that you can adjust antennas to
impedances other than 50 Ohms. This is handy if you are using CATV hardline, Ladder line or any other non
50 ohm coax.