MFJ MFJ-1642 User Manual

MFJ-1642 Portable Whip Tuner Instruction Manual

MFJ-1642 Portable Whip Tuner with Artificial Ground

IMPORTANT: Please read entire manual before attempting to operate this equipment. This unit does

not provide a dc or low frequency earth ground from the counterpoise terminal. A separate wire should be connected from the station ground bus to an electric ground. Do not place any counterpoise or noncoaxial feed wires near metallic or RF sensitive devices.

Introduction

The MFJ-1642 is a 150 watt, 80-10 meter antenna tuner designed for tuning short whips as well as virtually any random length wire antenna. It is perfect for either fixed station or portable use, and, with its built-in artificial ground tuning system, will match any transmitter or transceiver to virtually any antenna.

The MFJ-1642 tuner section uses a reversible "L" network. The advantage of the “L” network is that it has only two tuning controls, and only one tuning solution for given impedance match. The MFJ-1642 has rear panel connectors for coaxial input and a “Hi-Z/Lo-Z” switch for reversing the “L” network. An internal input -isolating current balun provides isolation of DC and RF grounds for optimum tuning of the RF counterpoise.

MFJ-1642 Supplied Components (30-10 meter operation)

• MFJ-1956 12 ft. telescopic whip antenna

• Counterpoise assembly (6, 14, and 26 ft. long wires)

MFJ-1642 Optional Components ( 40-80 meter operation)

• MFJ-63 Loading Coil Assembly for 40-80 meter operation with the MFJ-1956 12 ft.

telescopic whip antenna

Installation

1. Locate the MFJ-1642 in a convenient location at the operating position. Avoid placing the tuner near microphones, speech processors, computers, TNC's or other RF sensitive devices.

WARNING: High RF voltages exist at the antenna and counterpoise terminals. Avoid

touching these terminals while transmitting!

2. Connect your transceiver’s output to the SO-239 (UHF female) connector labeled TRANSMITTER on the back of the tuner. You will need an external SWR Wattmeter connected in line between the transmitter and whip tuner.

MFJ-1642 Portable Whip Tuner Instruction Manual

3. Conne ct the MFJ-1956 12 ft. telescopic whip antenna to the 3/8x24 stud on the top of the unit. For 40-80 meter operation with the MFJ-1956, you will need the optional MFJ-63 coil assembly.

Using the MFJ-1642

CAUTION: Never Change The Antenna or Inductor Selector Switch Position While

Transmitting! Never Apply More Than 150 Watts To The MFJ-1642.

Preset the controls on the MFJ-1642 as follows:

• ANTENNA to maximum inductance - Position "A".

• MATCHING to minimum capacitance – Position “10”

• NORM/+C switch to NORM

• COUNTERPOISE to minimum inductance – Position “L”

• Hi -Z/Lo-Z switch (back of unit) to Lo-Z.

Most modern solid state transceivers do not require tuning and loading adjustments. If the transceiver has a built in antenna tuner, be sure it is turned off or disabled. If your transmitter has an adjustable output circuit, it must be properly tuned to a 50 ohm load at the operating frequency before adjusting the tuner. This should be done with a dummy load.

Tuning Procedure

WARNING: Never transmit while changing the INDUCTOR SELECTOR.

1) First, tune for maximum receiver noise as follows:

• While listening to your desired receive frequency, adjust the ANTENNA control for

maximum receiver noise.

• Adjust the MATCHING control for maximum receiver noise.

• Adjust the COUNTERPOISE control for maximum receiver noise.

Note: If no noise peak is evident, try adding extra capacitance with the NORM/+C switch. Then reverse the HI-Z/LO-Z switch and re-try with both positions of the NORM/+C switch.

2) Apply just enough power on CW (or AM/FM/RTTY) to obtain a noticeable deflection on your external SWR Wattmeter.

3) Carefully adjust the ANTENNA, MATCHING and COUNTERPOISE controls for minimum SWR as follows.

• Adjust the MATCHING capacitor for minumum SWR.

• Adjust the COUNTERPOISE inductor for minimum SWR.

• Try plus or minus a position or two on the ANTENNA inductor, along with tuning the

MATCHING capacitor to see if lower SWR is achievable.

Note: These controls interact. Go back and forth between these adjustments as required until minimum SWR is obtained.

MFJ-1642 Portable Whip Tuner Instruction Manual

4) The transmitter power may now be increased up to a maximum of 150 watts. Note: The MFJ1642 will reduce the SWR of most antenna systems to below 1.5:1.

In Case of Difficulty

If this tuner fails to tune, please double check all connections and follow the tuning procedure again.

The power rating of this tuner is 150 watts on 80-10 meters. If this tuner arcs at the rated power levels, please double-check all connections and follow the tuning procedure again.

If you are still unsuccessful, please read the following ANTENNA HINTS text.

Grounding Hints

To minimize RFI, antennas should be kept away from other wiring as much as possible. Also, the antenna should be adequately insulated to prevent arcing or accidental contact if placed near other objects.

For safety, it is always best to use both dc and RF grounds. A DC ground may not be practical in some portable locations, however.

It is always important to have a good RF ground, provided by the counterpoise, when using any whip or long-wire antenna. This is because the MFJ-1642 tuner needs something to "push" against in order to force current into the antenna. If a good RF ground is not available, RF will usually find its way back into the power line (RFI), transmitter audio circuits (RF feedback), or the operator (RF burns).

Water pipes provide good dc and ac safety grounds, but they are often inadequate for RF grounding because they are long single conductors. RF grounds require large "spread out" surfaces with direct multipl e connections to the equipment ground point. Water pipes, heating ducts, or multiple ground rods may work (especially if they are all connected together with jumper wires), but the best RF grounds are radial systems or multi-wire counterpoises.

Antenna Hints

WARNING: For operator safety, a good earth ground should be installed and connected to

the case of the MFJ-1642. Make certain the safety ground connects to the same terminal that connects to the transmitter and other station accessories.

A binding post labeled "COUNTERPOISE" is provided for counterpoise or other RF ground connection(s). This post will not provide a safety ground.

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