MFJ MFJ-941E Operation & User’s Manual

1 MFJ VERSA TUNER II GENERAL INFORMATION: The MFJ-941E is designed to match virtually any transmitter to any antenna, including dipoles, inverted-vees, verticals, mobile whips, beams, random wires, and others fed by coax lines, balanced lines or a single wire. An eight-position antenna-selector switch provides versatile antenna selection. The MFJ-941E will handle up to 300 Watts of transmitter RF output power. The MFJ-941E employs a cross-needle meter so forward power, reflected power and SWR may be read simultaneously. CROSS-NEEDLE SWR/WATTMETER: The meter on the MFJ-941E may be used alone or with the tuner. Set the ANTENNA ...

2 INSTALLATION: 1. The tuner should be placed in a location where operation will be convenient. The ceramic feed through insulators will have high RF voltages if random wire or balanced line operation is used. These voltages can cause serious RF burns if touched when transmitting. NOTE : Locate the tuner so the rear is not accessible during operation. 2. The MFJ-941E should be installed between the transmitter and antenna. A coaxial line should be connected to the transmitter and the SO-239 coax TRANSMITTER connector on the back of the tuner. 3. One or two coax-fed antennas may be connected to the SO-239 coax connectors marke ...

3 MFJ-941E Front Panel USING THE MFJ- 941E: The INDUCTOR switch on the MFJ-941E represents maximum inductance at position "A" and the minimum inductance at position "L". Lower inductance is needed at higher frequencies than at low frequencies for the same impedance. The TRANSMITTER and ANTENNA controls represent maximum capacitance at position 10. For optimum operation of the MFJ-941E, the transmitter must be tuned to a 50 Ohm output impedance at the frequency of operation. The ANTENNA SELECTOR switch should be set to DUMMY LOAD for tuning up the transmitter. NOTE: The transmitter should always be tuned at a low output power ...

4 3. While transmitting a steady state carrier (CW) alternately adjust TRANSMITTER and ANTENNA controls for minimum SWR. Since both controls interact, the two controls can best be adjusted by turning the TRANSMITTER control one small increment at a time, then rotating the ANTENNA control for minimum SWR. Repeat this process until minimum SWR is obtained. ...

5 4. If a SWR of 1:1 is not achieved, the INDUCTOR control should be increased or decreased and Step 3 repeated. If arcing should occur between capacitor plates, the INDUCTOR control should be increased or decreased by one position, and Step 3 repeated. If SWR of 1:1 cannot be achieved, Step 3 should be repeated for each INDUCTOR control position. 5. After a minimum SWR is achieved, transmitter power may be increased to 300 Watts. The VERSA TUNER II will reduce the SWR of most feed systems to 1:1. In some cases, a 1:1 SWR is not achievable. In such cases, the length of the antenna may be increased or decreased to improve SWR ...

6 This problem often occurs on 80 meters if an odd quarter-wave (60 to 70 foot) open wire line is used to feed a half-wave (100 to 140 foot) dipole. The odd quarter-wave line transforms the dipole's low impedance to over three thousand Ohms at the tuner. This is because the mismatched feedline is an odd multiple of 1/4 wavelength long. The line inverts (or teeter-totters) the antenna impedance. ...

7 A problem also occurs on 40 meters with this antenna example. The feedline is now a multiple of a half-wave (60 to 70 foot) and connects to a full-wave high impedance antenna (100 to 140 foot). The half-wave line repeats the high antenna impedance at the tuner. The antenna system looks like several thousand Ohms at the tuner on 40 meters. The following suggestions will reduce the difficulty in matching an antenna with a tuner: 1. Never center feed a half-wave multi-band antenna with a high impedance feedline that is close to an odd multiple of a quarter-wave long. 2. Never center feed a full-wave antenna with any feedline ...

8 You can also send questions by mail to MFJ Enterprises, INC., P.O. Box 494, Mississippi State, MS 39762; by FAX to 601-323-6551; through Compuserve at 76206,1763; or by email to [email protected]. Send a complete description of your problem, an explanation of exactly how you are using your unit, and a complete description of your station. ...