Service Manuals, User Guides, Schematic Diagrams or docs for : . Rare and Ancient Equipment MFJ MFJ941B
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MFJ-941B VERSA TUNER II INSTRUCTIONS
Thank you very much for purchasing the MFJ-941B Versa Tuner II.
GENERAL INFORMATION
The MFJ-941B is designed to match virtually any transmitter to almost any antenna,
including dipoles, inverted vees, verticals, mobile whips, beams, random wires, and
others fed by coax lines, balanced lines, or a single wire, A 1:4 balun is built in for
connection to balanced lines. This unit will handle up to 300 watts of RF output
power from the transmitter from 160 through 10 meters. The MFJ-941B will monitor
either SWR or RF transmitter power in two ranges, 30W or 300W. The antenna selector
switch allows switching to one of the two coax fed antennas (direct or through tuner) and
either a balanced line antenna or random wire antenna. A bypass position allows
switching to a dummy load or a direct coax antenna. The tuner is bypassed but not the
meter circuit when antenna selector is switched to BYPASS, DIRECT COAX 1 or
DIRECT COAX 2 positions. CAUTION! Do not use the MFJ-941B for over 300 watts of
RF output power, even in the bypass or direct positions. Do not operate the antenna
selector while transmitting.
THE SWR/WATTMETER
The SWR/wattmeter of the MFJ-941B can be used with the tuner or by itself. The
SWR/wattmeter is between the transmitter and the tuner when the antenna switch is in the
COAX 1, COAX 2, or WIRE/BAL position. The SWR meter is sensitive down to
approximately 5 watts RF output, The SWR reading will not be accurate for a transmitter
power of less than 5 watts.
To read RF transmitter output power, simply push the SWR/WATT control in and set to
either 30 or 300, At position 30, the meter will read a maximum of 30 watts. At position
300, the meter will read a maximum of 300 watts.
To read SWR, turn the SWR/WATT control, with the control pushed in, for a full-scale
deflection and when pull the control out for the SWR reading. Note: The SWR sensitivity
must be reset for each power level to obtain an accurate reading.
INSTALLATION
1. Install the MFJ-941B between the transmitter and the antennas, A coax line is
connected between the transmitter and the SO-239 coax connector marked
TRANSMITTER on the tuner.
2. One or two coax fed antennas may be connected to the SO-239 coax connectors
marked COAX 1 and COAX 2. Note: Coax 1 and coax 2
antennas can be connected directly to the transmitter by turning the antenna selector
to COAX 1 DIRECT OR COAX 2 DIRECT,
3. A random wire antenna may be connected to the five-way binding post marked
WIRE. The random wire should be long, high, and as clear of surrounding objects
as possible. Do not ground the random wire antenna and make sure that the tuner is
well grounded to the transmitter. A five-way binding post, marked GND, is
provided for ground connection
4. A balanced line fed antenna may be connected to the two five-way binding posts
marked BALANCED LINE, along with a jumper wire from the WIRE binding post
to the adjacent BALANCED LINE binding post, as indicated by a dotted line on the
MFJ-941B, This couples the MFJ-941B to the balanced line through a 1:4 balun.
NOTE: Either a balanced line or random wire antenna can be connected at one
time. If a random wire antenna is used, make sure that there is not a jumper wire
between WIRE and BALANCED LINE.
5. An antenna or dummy load may be connected to the SO-239 coax connector
marked BYPASS COAX, The antenna switch on the BYPASS position will bypass
the turner and allow the MFJ-941B to be used as a SWR meter or wattmeter.
6. The mobile mounting bracket may be installed, if mobile operation is desired, by
first mounting the bracket to the selected location, Two #10-32 X 1/2" screws, two
#10 lockwashers, and two #10 nuts are provided. Second, slide the MFJ-941B into
the bracket and secure it with the four #6 X 3/8" sheet-metal screws also provided.
Use one of the four flat-washers provided between the bracket and,the bottom of the
tuner for each of the four #6 sheet-metal screws. NOTE: Do not over-tighten the
sheet-metal screws,
USING THE MFJ-941B
The INDUCTANCE switch on the MFJ-941B presents a minimum of inductance at
position A and a maximum of inductance at position L. Less inductance is needed at high
frequencies than at low frequencies for the same impedance. The TRANSMITTER and
ANTENNA controls both present a maximum of capacitance at position 1.
For optimum operation of the MFJ-941B,the transmitter must be tuned for a 50 ohm
output impedance for the frequency band in operation. The transmitter can be tuned with
the MFJ-941 connected by connecting the 50 ohm load to the BYPASS COAX connector
and turning the antenna switch to the BYPASS position. The MFJ-941B is then used only
as a SWR meter or a wattmeter. NOTE: Always tune the transmitter at a low output
power. After properly tuning the transmitter, turn the antenna switch to the desired
antenna and tune the tuner for a minimum SWR as described below. Do not readjust the
transmitter setting after loading it to the 50 ohm load,
1. Set the TRANSMITTER and ANTENNA controls to 3.5. (The capacitors are half-
opened.)
2. Rotate the INDUCTANCE control until maximum noise is obtained in the receiving
mode,
3. With the SWR/WATT control pushed in and set at 30, set the transmitter to the tune
position and transmit.
4. Turn the SWR/WATT control clockwise until a full-scale deflection is obtained. If a
full-scale deflection cannot be obtained, increase the output power from the
transmitter.
5. Pull the SWR/WATT control out for the SWR reading.
6. If the SWR is not 1:1, then tune the MFJ-941B for a minimum SWR.
7. While transmitting and with the INDUCTANCE control set the same as or Step 2.
alternately adjust the TRANSMITTER and ANTENNA
controls for a minimum SWR. Since the TRANSMITTER and ANTENNA controls
interact, the two controls can best be adjusted by turning the TRANSMITTER control
at a small increment at a time and then rotating the ANTENNA control for the
minimum SWR. Repeat this until a minimum SWR is obtained.
8. If a SWR reading, of 1:1 is not achieved, increase or decrease the INDUCTANCE
control one position and repeat Step 7. CAUTION: If arcing between capacitor plates
occurs, increase or decrease the INDUCTANCE control one position and repeat Step
7. NOTE: If a SWR of 1:1 cannot be achieved at this point, repeat Step 7 for each
INDUCTANCE control position. Again, do this in the tune mode or at a low
transmitter power,
9. After a minimum SWR. is achieved, readjust the SWR sensitivity by pushing the
SWR/WATT control in and adjust for a full-scale deflection. Pull out for the SWR
reading, The transmitter power may now be increased up to 300W. The SWR
sensitivity must be reset again after full power is applied. The ANTENNA and
TRANSMITTER controls may need fine adjustment if the SWR is not 1:1 at high
power, NOTE: On the 160 meter band, exces-
sive heating or arching may occur. Reduce the transmitter output power until it stops.
10. To read the transmitter power, push the SWR/WATT control in and set it to either 30
or 300.
11. A SWR of 1:1 can occur from more than one set of control settings on the MFJ-941B.
When a SWR of 1:1 is obtained, be sure to check the transmitter power and make
sure that the transmitter power is relatively high. If the transmitter power has
decreased substantially, try another INDUCTANCE control setting and repeat Step 7.
12. When using the MFJ-941B for receiving only, tune the MFJ-941B as described in
Step 1 and Step 2.
ADDITIONAL NOTES AND CAUTIONS
1. To read the transmitter power, push the SWR/WATT control in and
set it to either 30 or 300.
2. Do not operate the antenna switch while transmitting.
3. The SWR WATT control is factory calibrated for the 300W range, Do not reset the
knob on this control. However, due to component tolerance when precision reading is
desired, the 30W range can be recalibrated as follows: Push the SWR/WATT control
in. Set the control to 300, note the power level on the 300W scale, then rotate the
control clockwise to read the same power level on 30W scale. Mark the control
setting for the re-calibrated 30W range,
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