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MFJ -204b Instruction Manual

Antenna bridge
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Summary of Contents for MFJ mfj-204b

  • Page 2 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: (662) 323-5869; FAX: (662) 323-6551. Business hours: M-F 8-4:30 CST.

  • Page 3: Table Of Contents

    APPENDICES A. ZERO BEATING AGAINST A RECEIVER LIST OF FIGURES Figure 1 Front Panel Jacks and Controls Figure 2 End Panel Jacks Figure 3 Block Diagram Figure 4 MFJ-204B to Tuner Hook Up Figure 5 Schematic Diagram - 2 -...

  • Page 4: Introduction And Features

    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.

  • Page 5: Uses For The Mfj-204B

    Instruction and Technical Manual USES FOR THE MFJ-204B ANTENNA BRIDGE 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.

  • Page 6: System Controls And Indicators

    Front Panel Jacks and Controls FIGURE 1: Front Panel Jacks and Controls 1. Power On LED: Instantly know if the MFJ-204B is on or off with this bright LED. 2. Resistance Scale: This is where you read the resistance of your antenna using the calibration chart for your unit.

  • Page 7: Figure 2 End Panel Jacks

    Appendix A. 3. PWR: This 2.1 mm jack allows you to attach a MFJ-1312D AC adapter or feed power from your station supply.

  • Page 8: Theory Of Operation

    ________________________________________________________________ MFJ-204B Antenna Bridge Instruction and Technical Manual THEORY OF OPERATION Block Diagram FIGURE 3: Block Diagram Refer to Figure 3 and the Schematic diagram Figure 5 for this discussion of the theory of operation. RF is developed in the VCO consisting of L1 through L10 and the associated FETs Q1 and Q2 along with the variable capacitor.

  • Page 9: Mfj-204B Easy-Start Instructions

    The MFJ-204B requires the optional MFJ-1312D power supply adapter or a nine- volt transistor battery. If using a battery with the MFJ-204B ensure it is an ALKALINE nine-volt battery. Additionally you can use a 13.8 volt power supply by connecting a 2.1 mm plug to the cable with the positive wire connected to the center pin and the ground wire connecter to the outer pin.
  • Page 10 III. Using the MFJ-204B to adjust an antenna tuner. 1. Turn on the MFJ-204B 2. Attach the MFJ-204B to the tuner using the shortest length of RG-58U or RG-8U that you can. 3. Set the BAND switch to the appropriate band.
  • Page 11 Instruction and Technical Manual EASY START INSTRUCTIONS WARNING NEVER TRANSMIT WHILE THE MFJ-1702 COAX SWITCH IS SWITCHED TO A IF THE TRANSMITTER IS CONNECTED TO B. SERIOUS DAMAGE TO YOUR RADIO CAN OCCUR. TRANSMIT ONLY WHEN THE COAX SWITCH IS SWITCHED TO THE CONNECTOR TO WHICH THE TRANSMITTER IS CONNECTED.
  • Page 12 ________________________________________________________________ MFJ-204B Antenna Bridge Instruction and Technical Manual Figure 5: MFJ-204B Schematic Diagram - 11 -...
  • Page 13 The output of the MFJ-204B is a high level and damage to the front end of some radios may occur with a direct connection, so you assume all risks in making a direct connection.

  • Page 14: In Case Of Difficulty

    You can also send questions by mail to MFJ Enterprises, Inc., 300 Industrial Park Road, Starkville, MS 39759; by Facsimile (FAX) to 662-323-6551; or by email to techinfo@mfjenterprises.com.
  • Page 16 ONTH ARRANTY MFJ Enterprises, Inc. warrants to the original owner of this product, if manufactured by MFJ Enterprises, Inc. and purchased from an authorized dealer or directly from MFJ Enterprises, Inc. to be free from defects in material and workmanship for a period of 12 months from date of purchase provided the following terms of this warranty are satisfied.

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