MFJ MFJ-971 User Manual
MF J-9 71 QRP PORTABLE ANTENNA TUNER
GENERAL DESCRIPTION: The MFJ-971 is a compact 200-Watt portable tuner
compatibly packaged with. MFJ QRP t ra ns c eivers. The MFJ-971 is also a
perfect mate for any of today's ultra-compact SSB radios. It provides
a convenient cross-needle type SWR/Wattmeter and features a special
user-selectable 6-Watt range for QRP operation.
The T-match tuner covers 1.8-30 MHz and tunes al most any c oax, wire , or
balanced-feed type antenna (a 4:1 toroi d balun i s built in for balanced
line).
READING THE CROSS NEEDLE SWR INDICATOR: The MFJ-971 uses a crossneedle style meter to display FORWARD power, REFLECTED power, and SWR
simultaneously. To read Forward Power, observe the FORWARD meter
scale. To read Reflected Power, observe the REFLECTED meter scale.
To read SWR, observe where the two needles cross. The corresponding
red curve on the meter face displays your SWR reading. No "zero" or
"sensitivity" adjustment is required with cross-needle SWR displays.
POWER LEVELS: The FORWARD scale is calibrated from 0-300 Watts and
the REFLECTED scale from 0-60 Watts. In the high-power range, read
both scales directly (x 1). In the 30 Watt range, move the decimal
point one place to the left (x 0.1).
For QRP sensitivity (6-Watts FORWARD, 1.2-Watts REVERSE), you must
perform a simple conversion to ob tain actual power . You can convert
in your head by moving the decimal point two places to the left and
doubling the reading (ie. 300 W = 3.00 x 2 = 6 W). You may also multiply
the scale reading times 0.02 on a pocket calculator -- or use this
conversion chart:
FORWARD SCALE
300W 30W QRP
----------------- ---------------300W 30W 6W 60 w 6w 1.2W
250W 25W 5W 50W 5 W 1.0W
200W 20W 4W 40W 4 W 0.8W
150W 15W 3W
100W 10W 2W 20W 2 W 0.4W
50W 5W 1 W 10W 1 W 0.2W
SELECTING POWER RANGE: The "IN" position of the meter's range
switch selects the 30-W range. The "OUT" position provides a choice
of 300-W or 6-W QRP range, as determined by two jumpers on the
powermeter pc board (see Figure 1A,1 B). W hen jumpe r plugs are
installed in position "A", meter sensitivity is 6-Watts (QRP). When
installed in position "B", sensitivity is 300-Watts. Jumpers are
normally set for "B" (High Power) at th e factory .
REFLECTED SCALE
60W 6W QRP
0
3
3 W 0.6W
w
CAUTION: Running high power while in the "QRP" range could damage your
meter movement.
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INSTALLING YOUR TUNER: The MFJ-971 tuner may be stacked with a
companion MFJ transceiver and power pack, or used separately.
Two brackets and 8 screws are included in this package to connect
the tuner to the MFJ transceiver and power pack if you choose to do
so. Locate your tuner to prevent accidental contact with connectors
on the rear panel; even low-power radios can cause serious RF burns
when fed into a random wire antenna. The tuner meter lamp may be
powered from any 12-VDC source. Use a 5.5mm x 2.1mm coaxial plug;
center pin positive (+).
TUNER CONNECTIONS: Set u p your MFJ-971 as follows:
1. Connect radio to the SO-239 connector marked TRANSMITTER. 2.
Connect antenna feed to the appropriate tuner output:
(a.) COAX-FEED to the SO-239 connector marked ANTENNA.
(b.) RANDOM WIRE to the red binding post below ANTENNA jack.
(c.) BALANCED FEEDERS to the BALANCED binding posts.*
* WHEN USING BALANCED FEEDLINE, CONNECT A SHORT JUMPER FROM THE
LOWER "BALANCED" BINDING PO ST TO THE RED "ANTENNA" BINDIN G POST.
This routes the balun's unbalanced output to the tuner circuit.
3. Connect your tuner and transmitter to a good earth ground.
CAUTION: For reasons of safety and radiation efficiency, random wire
antennas should be high, clear of obstructions, and at least 1/4
wavelength long. They should also be well insulated from humans,
animals, vegetation, and gr ounded objects.
OPERATING YOUR TUNER: If your radio has tube finals, set the
transmitter on-frequency and "tune up" into a 50-Ohm resistive load.
Once this is done, leave your TUNE and LOAD controls set and
connect the tuner. If you r radi o has solid-state finals, omit this
step (it is already matched to
-
a 50-Ohm non-reactive load).
1. REDUCE TRANSMITTER OUTPUT before making initial adjustments.
2. Set tuner's TRANSMITTER and ANTENNA controls at 12:00 (3-1/2). 3
Switch INDUCTANCE for loudest receiver background noise.
4 . Transmit a steady carrier (at low power), alternat
ely
=
adjusting TRANSMITTER and ANTENNA controls for minimum SWR.
NOTE: Since these controls interact, try moving the TRANSMITTER
control a small increment, then rotate the ANTENNA control for
minimum SWR. Repeat until you obtain the lowest SWR possible.
5. If you cannot obtain a 1:1 match, increase or decrease
INDUCTANCE and repeat step 4. Also, if RF arcing occurs
inside the tuner, change INDUCTANCE and repeat step 4).
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