MFJ MFJ-941E User Manual

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MFJ-941E Versa Tuner II

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 W atts of transmitter RF output power. The MFJ-941E employs a cross-needle m eter so forward power, reflected power and SW R may be read simultaneously.

CROSS-NEEDLE SWR/WATTMETER:

The meter on the MFJ-941E may be used alone or with the tuner. Set the

SELECTOR

COAX 1 DIRECT

COAX 2 DIRECT

ANTENNA

to use the meter without the tuner. T he MFJ-941E utilizes a cross-needle meter so FORW ARD power, REFLECTED power and SWR may be read simultaneously in two ranges. FORW ARD power m ay be read by setting the power range switch to HI (

Watts) or LO (30 W atts). Next read the power level on the FORWARD

300

SCALE. REFLECTED power is shown simultaneously on the REFLECTED SCALE. SWR is determined by observing the intersection point of the two needles. No SWR sensitivity adjustment is needed to read SWR. The HI range is

Watts FORWARD and 60 Watts REFLECT ED.

300

The LO range is 30 Watts F ORWARD and 6 Watts REF LECT ED. The difference between the HI and LO scales readings is a factor of 10.

The meter lamp can be powered by a 12 Vdc source, such as the optional MFJ-1312B power supply. Use a 2.1mm coax ial plug with the center conductor of the plug c onnected to the positive and the sleeve connected to ground. The

METER LAMP ON/OFF

switch will activate the meter

lamp.

ANTENNA SELECTOR:

The

ANTENNA SELECTOR

LINE, COAX 1

, and

operation. An external 50 Ohm dummy load can be connected to the

COAX 2

switch utilizes eight positions. They are

positions for both

BYPASS

(direct) and

DUMMY LOAD, BALANCE

TUNED

(through) the tuner

EXT LOAD

connector located at the rear of the tuner. Do not continuously key into the dumm y load f or more than 2 minutes at a time.

CAUTION:

Never use the MFJ-941E for

DIRECT

DUMMY LOAD

positions.

OVER 300 Watts

of RF output power, even in the

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MFJ-941E Versa Tuner II

INSTALLATION:

The tuner should be placed in a location where operation will be convenient. The ceram ic

feed through insulators will have high RF voltages if r andom 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.

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 the back of the tuner.

TRANSMITTER

connector on

One or two coax-fed antennas m ay be connected to the SO-239 coax connectors mark ed

COAX 1

COAX 2

transmitter, bypassing the tuner, by setting the

DIRECT

COAX 2 DIRECT

. Coax 1 and Coax 2 antennas may be connected directly to the

ANTENNA SELECTOR

switch to

, respectively.

A random wire antenna may be connected to the five-way binding post marked random length wire should be long, high, and as clear of surrounding objects as possible. For optimum oper ation, the wire antenna should be a quarter wave-length or longer at the operating frequency. Do NOT ground the r andom wire antenna. The tuner s hould be wellgrounded to the transmitter. A binding post marked connections.

A balanced line-fed antenna may be connected to the two five-way binding posts marked

BALANCED LINE

. A jumper wire from the

binding post, as indicated by a dotted line

WIRE

GROUND

on the MFJ-941E, should be connected to one of the posts of the couples the MFJ-941E to the balanced line through a 4:1 balun.

NOTE :

Either a balanced line or a random wire antenna m ay be connected to the MFJ-941E at one time. If a random length wire is used, care should be taken to assure that no jumper wire is between the

An external 50 Ohm dum m y load may be connected to the

binding post and the

WIRE

BALANCED LINE

EXT. DUMMY L OAD

is provided for ground

BALANCE LINE

located at the rear of the tuner.

COAX 1

. The

WIRE

. This

connector

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MFJ-941E Versa Tuner II

MFJ-941E Front Panel

USING THE

The

INDUCTOR

MFJ-941E:

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

SELECTOR NOTE: The transmitter should always be tuned at a

After the transmitter is properly tuned, the

switch should be set to

DUMMY LOAD

ANTENNA SELECTOR

antenna and the tuner adjusted for a minim um SW R as described below. transmitter loading control setting after loading it to 50 Ohms.

NOTE: TUNER ADJUSTMENT:

When using the MFJ-941E for receiving only, tune as described in Steps 1 and 2.

Set the half-open.

TRANSMITTER

Rotate the

INDUCTOR

and

ANTENNA

control until maxim um noise is obtained with the transceiver in the

for tuning up the transmitter.

low output power

should be set to the desired

DO NOT

controls to 5. In this position the capacitors are

ANTENNA

readjust the

receiving mode.

CAUTION: Do not operate the ANTENNA selector switch while transmitting!.

While transmitting a steady state carrier (CW) alternately adjust

ANTENNA

best be adjusted by turning the rotating the

controls for m inimum SW R. Since both controls interact, the two controls can

control one small increment at a time, then

ANTENNA

TRANSMITTER

control for minimum SWR. Repeat this process until minimum

TRANSMITTER

and

SWR is obtained.

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MFJ-941E Versa Tuner II

If a SW R of

and Step 3 repeated. If arcing should occur between capacitor plates, the

is not achieved, the

1:1

INDUCTOR

control should be increased or decreased

INDUCTOR

control should be inc reased or dec reased by one position, and Step 3 repeated. If SW R of

cannot be achieved, Step 3 should be repeated for each

1:1

After a m inimum SWR is achieved, tr ansmitter power may be increased to 300 Watts. The

VERSA TUNER II will reduce the SWR of m ost f eed systems to

INDUCTOR

1:1

control position.

. 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.

SWR of

an SWR of transmitter power has decr eased substantially, try another

may occur at more than one set of control settings on the MFJ-941E. When

1:1

is obtained, make sure that the transmitter power is relatively high. If

1:1

INDUCTOR

control setting and

repeat Step 3.

In Case Of Difficulty:

If this tuner

fails to tune,

again. Be sure you are using enough inductance (lowest letter usable for band) and have the capacitors open far enough (highest front panel number).

If this tuner

at the rated power levels, please

arcs

tuning procedures again. Be sure you are using the least amount of inductance and the greatest capacitance possible to match the load on the operating frequency. If you are still

unsuccessful, please read the

NOTE:

If this tuner transmitter output power.

please

double check all connections

Antenna Matching Problems

when operating on the

arcs

and follow the tuning procedures

double check all connections

text below.

160 meter

band, it may be necessary to reduce

and follow the

Antenna Matching Problems:

Most matching problem s occur when the antenna system presents an extremely high impedance to the tuner. W hen the antenna impedanc e is much quarter-wavelength feedline conver ts the low antenna impedance to a

the tuner

. A similar problem occurs if the antenna has an extremely high impedance and the transmission line is a multiple of a half-wavelength. The half-wavelength line repeats the very high antenna impedance at the tuner.

antenna system very difficult or

Incorrect feedline and antenna lengths can make an

impossible

to tune.

This problem often occurs on 80 meters if an odd quarter-wave (60 to 70 f oot) 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 f eedline is an odd multiple of 1/4 wavelength long. The line inverts (or teeter-totters) the antenna impedance.

than the feedline impedance, an odd

lower

very high impedance at

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MFJ-941E Versa Tuner II

d d d

A problem also occurs on 40 m eters with this antenna exam ple. T he feedline is now a multiple of a half-wave (60 to 70 foot) and connects to a f ull- wave high im pedanc e antenna (100 to 140 foot). The half-wave line r epeats the high antenna impedance at the tuner. T he antenna system looks like several thousand Ohms at the tuner on 40 meters. T he following suggestions will reduce the difficulty in matching an antenna with a tuner:

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. Never center feed a full-wave antenna with any feedline close to a multiple of a half-wave

long. If a tuner will not tune a multi-band antenna, add or subtrac t 1/8 wave of feedline (for the

band that won't tune) and try again. Never try to load a G5RV or center fed dipole on a band below the half-wave design

frequency. If you want to operate an 80 meter antenna on 160 meters, feed either or both conductors as a longwire against the station ground.

To avoid problems m atching or feeding any dipole antenna with high impedance lines, keep the lines around these lengths [ The worst possible line lengths are shown in brackets ]:

160 meter

80 meter 40 meter

NOTE:

Some trimming or adding of line may be necessary to accommodate higher bands.

35-60, 170-195 or 210-235 feet. 34-40, 90-102 or 160-172 feet. 42-52, 73-83, 112-123 or 145-155 feet.

[

Avoid 130, 260 ft ]

[

Avoid 66, 135, 190 ft ]

[

Avoid 32, 64, 96, 128 ft ]

WARNING:

To avoid problems, a dipole antenna should be a f ull half-wave on the lowest band. On 160 meters, an 80 or 40 meter antenna fed the normal way will be extremely reactive with only a few Ohms of f eedpoint resist ance. T rying to load an 80 meter (or higher frequency) antenna on 160 meters can be a disaster for both your signal and the tuner. The best way to operate 160 with an 80 or 40 meter antenna is to load either or both f eedline wires (in parallel) as a longwire. The antenna will act like a "T" antenna worked against the station ground.

Technical Assistance

If you have any problem with this unit first check the appropriate section of this manual. If the manual does not reference your problem or your problem is not solved by reading the manual, you may call MFJ Technical Service at

601-323-0549

have your unit, manual and all information on your station handy so you can answer any questions the technicians may ask.

You can also send questions by mail to MFJ Enterprises, Inc., 300 Industrial Park Road, Starkville, MS 39759; by Facsimile to 601-323-6551; 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.

Schematic:

or the MFJ Factory at

601-323-5869

. You will be best helped if you

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