MFJ MFJ-928 User manual

INSTRUCTION MANUAL
CAUTION: Read All Instructions Before Operating Equipment
MFJ ENTERPRISES, INC.
300 Industrial Park Road
Starkville, MS 39759 USA
Tel: [phone] Fax: [phone]
COPYRIGHT 200 MFJ ENTERPRISES, INC.5
C
Model MFJ-928
VERSION 0A
Compact IntelliTuner
Automatic Antenna Tuner
TM

MFJ-928 Compact IntelliTuner Automatic Antenna Tuner Instruction Manual
©2005 MFJ Enterprises, Inc.
i
Contents
THE BASICS
Introduction...................................................................................................................................... 1
Features............................................................................................................................................ 2
Specifications................................................................................................................................... 2
Fast Start .......................................................................................................................................... 3
Front Panel....................................................................................................................................... 4
SWR LED........................................................................................................................... 4
TUNE LED ......................................................................................................................... 4
TUNE Button...................................................................................................................... 4
Automatic/Semi-Automatic Tuning Mode ............................................................ 4
ANT Button ........................................................................................................................ 5
POWER Button................................................................................................................... 5
Back Panel ....................................................................................................................................... 6
Power .................................................................................................................................. 6
Radio Interface.................................................................................................................... 6
Transmitter.......................................................................................................................... 9
Antenna 2............................................................................................................................ 9
Antenna 1............................................................................................................................ 9
Ground ................................................................................................................................ 9
Wire .................................................................................................................................... 9
Installation ..................................................................................................................................... 10
MISCELLANEOUS
Antenna Memory ........................................................................................................................... 11
IntelliTuneTM Algorithm ................................................................................................................ 11
LC Limits....................................................................................................................................... 11
Morse Code and Beeps .................................................................................................................. 12
Foldback Circuit ............................................................................................................................ 12
Grounding Hints ............................................................................................................................ 13
Antenna System Hints.................................................................................................................... 13
Location ............................................................................................................................ 13
Matching Problems ........................................................................................................... 13
APPENDICES
Resetting the Tuner........................................................................................................................ 15
Factory Defaults................................................................................................................ 15
Delete Entire Antenna Memory ........................................................................................ 16
Delete Antenna Memory Bank ......................................................................................... 16
Total Reset ........................................................................................................................ 16
Self Test ......................................................................................................................................... 17
Power-Down Circuit Test .............................................................................................................. 18

MFJ-928 Compact IntelliTuner Automatic Antenna Tuner Instruction Manual
©2005 MFJ Enterprises, Inc.
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Relay Test ...................................................................................................................................... 18
Frequency Counter Calibration...................................................................................................... 19
SWR Bridge Calibration ................................................................................................................ 19
In Case of Difficulty ...................................................................................................................... 20
Technical Assistance...................................................................................................................... 21
List of Accessories......................................................................................................................... 21
Circuit Block Diagram................................................................................................................... 22
FIGURES
Figure 1. Installation Block Diagram.............................................................................................. 3
Figure 2. MFJ-928 Front Panel....................................................................................................... 4
Figure 3. Button Action .................................................................................................................. 5
Figure 4. MFJ-928 Back Panel ....................................................................................................... 6
Figure 5. Rado Interface Connector................................................................................................ 6
Figure 6. Alinco Interface Cable..................................................................................................... 7
Figure 7. Icom Interface Cable ....................................................................................................... 8
Figure 8. Kenwood Interface Cable ................................................................................................ 8
Figure 9. Yaesu Interface Cable (FT-100, FT-817, FT-857, FT-897) ............................................ 8
Figure 10. Yaesu Interface Cable (FT-847) .................................................................................... 9
Figure 11. Power-On Operations .................................................................................................. 15
Figure 12. MFJ-928 Circuit Block Diagram................................................................................. 22
TABLES
Table 1. Jumper JP2 Setting............................................................................................................ 7
Table 2. Memory Resolution ........................................................................................................ 11
Table 3. Tuner Beeps .................................................................................................................... 12
Table 4. Failure Messages............................................................................................................. 17

MFJ-928 Compact IntelliTuner Automatic Antenna Tuner Instruction Manual
©2005 MFJ Enterprises, Inc.
1
The Basics
Introduction
The MFJ-928 IntelliTunerTM lets you rapidly tune any antenna automatically: unbalanced or single-wire.
MFJ's exclusive InstantRecallTM, IntelliTuneTM and AdaptiveSearchTM algorithms give you fast automatic
tuning with more than 20,000 non-volatile VirtualAntennaTM memories. Each of the two antennas has
four banks of memory; each memory bank has over 2500 non-volatile memories for tuner settings.
The tuner includes a highly efficient switching L-network with wide matching capability, 1.8 to 30 MHz
coverage, a radio interface port, and heavy-duty 10 amp/1000 volt relays. It is rated at 200 watts
SSB/CW.
A maximum of 256 values of inductance and 256 values of capacitance are available. With the
capacitance switched between the input and output side, this provides a total of 131,072 L/C tuning
combinations. The nominal tuning ranges are 0 to 24 μH and 0 to 3900 pF.
All MFJ IntelliTunersTM learn and remember. When you transmit, they automatically adjust for minimum
SWR and remember the frequency and tuner settings, safely stored in non-volatile memory. The next
time you operate on that frequency (or close to it) and antenna, these tuner settings are instantly restored
and you’re ready to operate in milliseconds. Each of two antenna selections has four banks of memory,
which can learn and remember more than 2500 frequencies and tuner settings per bank.
When you key your transmitter, MFJ’s InstantRecallTM checks its memory to see if you have operated
that frequency before. If so, tuning is instantaneous and you’re ready to operate. If not, MFJ’s
IntelliTuneTM algorithm (based on MFJ’s famous SWR Analyzer technology) kicks in. It measures the
complex impedance of your antenna. Next, it calculates the components it needs and instantly snaps them
in. Finally, it fine-tunes to minimize SWR, and you’re ready to operate--all in a fraction of a second.
If the antenna impedance is not within the tuner’s measurement range, MFJ’s AdaptiveSearchTM
algorithm goes into action. Frequency is measured and relevant components values are determined. Only
those values are searched for fast tuning. If it still cannot find a match, the search is performed again
using a different search pattern.
All MFJ’s IntelliTunersTM support radio tuner interfaces that are compatible with Alinco EDX-2 tuner,
Icom AH-3 and AH-4 tuners, Kenwood AT-300 tuner, Yaesu FC-30 tuner, and certain Yaesu radios with
CAT system. Optional interface cables MFJ-5114A (for Alinco), MFJ-5114I (for Icom), MFJ-5114K (for
Kenwood), and MFJ-5114Y, MFJ-5114Y2 and MFJ-5124Y3 (for Yaesu) are available from MFJ
Enterprises, Inc.
The tuners enter a “sleep” mode when idle and when no transmit signal is present, turning off the
microprocessor clock to avoid the generation of spurious signals.

MFJ-928 Compact IntelliTuner Automatic Antenna Tuner Instruction Manual
©2005 MFJ Enterprises, Inc.
2
Features
• Automatically matches antennas from 6 to 1600 ohms impedance (SWR up to 32:1)
• Handles 200 watts SSB/CW
• Tune in less than 15 seconds, usually less than 5 seconds
• Over 20,000 non-volatile memories for tuner settings
• Four memory banks per antenna with over 2500 memories per bank
• Highly efficient switching L-network matching circuit
• 1.8 to 30 MHz continuous frequency coverage
• Audio SWR meter
• Built-in frequency counter
• Built-in radio interface circuitry for compatible radios
• Built-in bias tee
• Two SO-239 coax fed antenna connectors
• Connector for random wire or single wire antennas
Specifications
• Impedance matching range: 6 to 1600 ohms
• SWR matching range: up to 8:1 for < 50 ohms and up to 32:1 for > 50 ohms
• Minimum power for tuning: 2 watts
• Maximum power while tuning: 100 watts with foldback, 20 watts without foldback
• RF power limit: 200 watts SSB/CW
• Frequency range: 1.8 to 30 MHz continuous coverage
• Frequency counter accuracy: ±1 kHz across HF bands
• Frequency counter range: up to 50 MHz
• Capacitance range: 0 to 3961 pF nominal (256 values)
• Inductance range: 0 to 24.86 μH nominal (256 values)
• Relay rating: 10 amp 1000 volts
• Relay electrical life: 100,000 operations
• Relay mechanical life: 10 million operations
• Memory endurance: 1 million erase/write cycles
• Memory data retention: > 200 years
• Power requirements: 12 - 15 volts DC, 2.1 × 5.5 mm coaxial plug, center pin positive
• Current consumption: 750 milli-amp or less
• Dimensions (approx.): 6.5 × 2.8 × 7.5 in. (165 × 71 × 191 mm) (width/height/depth)
not including connectors
• Weight (approx.): 2.3 lb. (1.04 kg)
† Specifications and design are subject to change without notice.

MFJ-928 Compact IntelliTuner Automatic Antenna Tuner Instruction Manual
©2005 MFJ Enterprises, Inc.
3
Fast Start
WARNING
●Never operate the tuner with its cover removed. Contact with the components inside the
tuner while transmitting will result in painful RF burns.
●Locate the tuner so that the rear terminals are not accessible during operation. The single
wire connection may have high voltage while transmitting.
●Disconnect all antennas from the tuner during lightning storms.
●Always tune with low power (about 10 watts). Apply maximum power only after tuning up.
●Never exceed tuner specifications.
●Do not transmit with a high SWR for extended periods of time.
1. Connect the MFJ-928 to a 12-15 VDC voltage source capable of supplying at least 750 milli-amps.
2. Connect your transmitter to the TRANSMITTER connector using a 50-ohm coaxial cable.
3. Connect your coax-fed antenna to the ANTENNA 1 connector using a 50-ohm coaxial cable, or
connect your random wire to the WIRE binding post.
4. Connect your ground connection to the GROUND post.
5. Press the [POWER] button to turn on the MFJ-928 tuner.
6. Press the [ANT] button momentarily until there is one beep. One beep indicates that antenna 1 is
selected.
7. Key your transmitter to output a carrier of 10 watts CW, FM or AM.
8. Press and hold the [TUNE] button on the MFJ-928 for one second to start the automatic tuning
process. When completed, check to ensure an SWR of 2.0 or less before increasing RF power.
9. You are ready to transmit.
Note: During the automatic tuning process, the tuner will make some noise. These are the relays
switching at a very fast pace and it is normal operation. Do not be alarmed.
Note: When the tuner power is OFF, the tuner is in bypass mode and RF from the transmitter goes
directly to the antenna (ANTENNA 1) with no matching. When the tuner power is ON,
pressing [TUNE] quickly places the tuner in bypass mode (zero inductance and zero
capacitance) and indicates by one beep.
Transmitter MFJ-928
50-ohm Coax
Antenna 1
RF Ground 12 VD
C
A
ntenna 2
Figure 1. Installation Block Diagram.

MFJ-928 Compact IntelliTuner Automatic Antenna Tuner Instruction Manual
©2005 MFJ Enterprises, Inc.
4
Front Panel
Figure 2. MFJ-928 Front Panel.
• SWR LED: A green LED that illuminates when the SWR is 1.5 or less.
• TUNE LED: A red LED that illuminates when the automatic tuning is in progress.
• TUNE Button: Has three different functions based on the length of time you press and hold it before
releasing. Press [TUNE] quickly (less than 0.5 second) to bypass the tuner. One beep indicates
bypass mode, where RF from the transmitter goes directly to the antenna with no matching. A second
quick press toggles the tuner back to its last L/C setting, and the tuner responds with two beeps.
Press and hold [TUNE] for 0.5 to 2 seconds to start the automatic tuning process. The transmitter
must be keyed first with at least two watts of power. When the SWR is already below the target SWR
of 1.5, pressing [TUNE] will fine-tune the match for a lower SWR, if possible. When the automatic
tuning is completed, a series of beeps indicates the tuned SWR where one beep indicates SWR of 1.5
or less, two beeps indicate SWR of 1.6 to 2.0, three beeps indicate SWR of 2.1 to 2.5, and four beeps
indicate SWR of 2.6 to 3.0. For SWR above 3.0, “SWR” (di-di-dit di-dah-dah di-dah-dit) will be sent
on CW.
“StickyTune” allows for one-handed tuning operation. Normal tuning requires keying the transmitter
with one hand and using the other hand to push the [TUNE] button to start the tuning process. To
toggle the StickyTune mode on and off, press and hold the [TUNE] button for two seconds. One beep
indicates on and two beeps indicate off. When enabled, the tuning process starts automatically when
the transmitter is keyed with at least two watts of power regardless of the SWR. This works in both
automatic and semi-automatic modes.
Automatic/Semi-Automatic Tuning Mode
Pressing [TUNE] and [ANT] simultaneously toggles between automatic and semi-automatic tuning
mode. One beep indicates automatic mode and two beeps indicate semi-automatic mode. In
automatic mode, the tuning routine is automatically started when at least two watts of power is
applied and the SWR is greater than 2.5. In semi-automatic mode, the tuning routine starts only when
the [TUNE] button is pressed for 0.5 to 2 seconds.

MFJ-928 Compact IntelliTuner Automatic Antenna Tuner Instruction Manual
©2005 MFJ Enterprises, Inc.
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Note: During the tuning process, the tuner will make some noise. These are the relays
switching at a very fast pace and it is normal operation. Do not be alarmed.
• ANT Button: Has two different functions based on the length of time you press and hold it before
releasing. Press [ANT] quickly (less than one second) to select the antenna to tune. Press button to
toggle between Antenna 1 and Antenna 2. One beep indicates Antenna 1 and two beeps indicate
Antenna 2. A single-wire antenna is, by default, Antenna 1.
Press and hold [ANT] for one second to cycle among the four memory banks of the current antenna.
The selected bank is indicated by a series of short beeps, where one beep indicates bank A, two beeps
indicate bank B, three beeps indicate bank C, four beeps indicate bank D, and five beeps indicate
antenna memory is OFF. See “Antenna Memory” on page 11.
Pressing the [ANT] button will switch the antenna or bank only when there is no RF power; also, the
tuner setting for the selected antenna and bank, if available, is instantly restored from memory when
enabled.
• POWER Button: Used to turn the power on and off. When the power is off, the tuner is placed in
bypass mode and Antenna 1 is selected. When turning on the power, the tuner automatically restores
all previous settings and displays the target SWR on the main screen.
WARNING: Do not turn the power on and off rapidly, otherwise the tuning setting
memory can be corrupted and the unit will have to be reset to factory defaults.
Note: When the tuner power is OFF, the tuner is in bypass mode and RF from the transmitter
goes directly to the antenna (ANTENNA 1) with no matching.
BUTTON ACTION
Press + to toggle between automatic and semi-automatic mode.
ANT
TUNE
POWER
Press less than 0.5 second to toggle bypass mode; press and hold for 0.5 to 2 seconds to start the
tuning process; press and hold for more than two seconds to toggle the StickyTune on and off.
Press less than one second to toggle between antenna 1 and antenna 2; press and hold for more
than one second to cycle the 4 antenna memory banks.
Press in to turn power on, out to turn power off.
TUNE ANT
Figure 3. Button Action.

MFJ-928 Compact IntelliTuner Automatic Antenna Tuner Instruction Manual
©2005 MFJ Enterprises, Inc.
6
Back Panel
RADIO
INTERFACE
+
POWER
12VDC
750mA
WIRE
MFJ ENTERPRISES, INC.
STARKVILLE, MS USA
GROUND
!
Do not connect
WIRE and
ANTENNA 1
at same time!
TRANSMITTER ANTENNA 2 ANTENNA 1
Figure 4. MFJ-928 Back Panel.
• Power: This jack accepts a standard 2.1 × 5.5 mm coaxial plug with positive center and negative
sleeve. The tuner requires 12 volts DC at up to 750 milli-amps. The use of a regulated supply is not
mandatory but is recommended for best performance. An optional 12 volts DC 1.5 amp power
supply, the MFJ-1316, is available from MFJ Enterprises, Inc.
WARNING: Do not apply voltages greater than 18 volts to this unit, or permanent damage
to the unit may result.
Note: When the tuner power is OFF, the tuner is in bypass mode and RF from the transmitter
goes directly to the antenna (ANTENNA 1) with no matching.
• Radio Interface: An 8-pin modular (RJ-45)
connector for connecting to the tuner interface
connector of compatible radios. Most radios
provide +13.8 VDC power thought its tuner
interface connector. If separate power
supplies are used to power the MFJ-928, the
MFJ-928 should be powered on first (both
LEDs blink once) and then turn on the radio,
so the radio knows an external tuner is
attached. The radio will disable its internal
tuner, if it has one, and use the external tuner.
The Radio Interface works with radios that are compatible with Alinco EDX-2, Icom AH-3 and AH-
4, Kenwood AT-300, and certain Yaesu radios with CAT system. When connected to a compatible
radio, simply press the [TUNER] or [AT] button on the radio; for certain Yaesu, press the [TUNE]
button on the tuner to start the automatic tuning process. The radio will automatically switch to CW
mode (AM for Yaesu), transmit a 10-watt carrier, and start the tuning process. Once the automatic
tuning is completed, the radio will return to its previous mode and power setting.
+13.8 V DC input ( 50 mA)
+13.8 V DC input ( 50 mA)
+13.8 V DC input ( 50 mA)
Ground
Ground
Key/TT/TX
TX INH
Start/TS/RX
7
7
7
7
8
6
5
4
3
2
1
12345678
Rear Panel View
Figure 5. Radio Interface Connector.

MFJ-928 Compact IntelliTuner Automatic Antenna Tuner Instruction Manual
©2005 MFJ Enterprises, Inc.
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WARNING: Make sure the +13.8 volts connection on the radio’s tuner port is capable of
supplying at least 750 mA of current, since the MFJ-928 uses up to 750 mA.
Jumper JP2, located behind the front panel circuit board, selects the radio to be connected to the
Radio Interface connector. Set this jumper to the “I” position to interface with radios that are
compatible with the Alinco EDX-2 tuner, Icom AH-3 and AH-4 tuners (also for interfacing to the
MFJ-5124Y3). Set the jumper to the “K” position to interface with radios that are compatible with
Kenwood AT-300 tuner. Set the jumper to the “Y” position to interface with Yaesu FT-100; “1”
position to interface with Yaesu FT-817, FT-857 or FT-897; and “2” position to interface with Yaesu
FT-847. If no cable is connected to the Radio Interface connector, set the jumper to the “0” position
to disable the interface. Default is “0”.
Jumper JP2 To Interface Using
0 No Radio Interface --
I Alinco
Icom
Yaesu TUNER (FT-857/897)
MFJ-5114A
MFJ-5114I
MFJ-5124Y3
K Kenwood MFJ-5114K
Y Yaesu CAT (FT-100) MFJ-5114Y
1 Yaesu CAT (FT-817/857/897) MFJ-5114Y
2 Yaesu CAT (FT-847) MFJ-5114Y2
3 Reserved --
4 Reserved --
Table 1. Jumper JP2 Setting.
The MFJ-5114A interface cable provides power and control between an Alinco radio and the MFJ
automatic tuner. Supported Alinco radios are DX-70, DX-77, and any Alinco radio that supports the
Alinco EDX-2 tuner.
Pin 1 (Ground) connects to pins 4 and 5 of Radio Interface Plug.
Pin 2 (+13.8V) connects to pins 2 and 3 of Radio Interface Plug.
Pin 3 (Key) connects to pin 6 of Radio Interface Plug.
Pin 4 is not connected.
Pin 5 (Start) connects to pin 8 of Radio Interface Plug.
5
1
2
3
4
Figure 6. Alinco Interface Cable.
The MFJ-5114I interface cable provides power and control between an Icom radio and the MFJ
automatic tuner. Supported Icom radios are IC-706, IC-707, IC-718, IC-725, IC-728, IC-736, IC-738,
IC-746, IC-756, IC-765, IC-775, and any Icom radio that supports the Icom AH-3 or AH-4 tuner.
Push and hold the radio’s [TUNER] button for two seconds to start the tuning process. Push
[TUNER] quickly to bypass the tuner.

MFJ-928 Compact IntelliTuner Automatic Antenna Tuner Instruction Manual
©2005 MFJ Enterprises, Inc.
8
Pin (Key) connects to pin 6 of Radio Interface Plu
Pin (Start) connects to pin 8 of Radio Interface Plug.
Pin (Ground) connects to pins 4 and of Radio Interface Plug.
2
Pin 3 (+13.8V) connects to pins 2 and 3 of Radio Interface Plug.
45
1g.
1
2
3
4
Figure 7. Icom Interface Cable.
The MFJ-5114K interface provides power and control between a Kenwood radio and the MFJ
automatic tuner. Supported Kenwood radios are TS-50S, TS-450S, TS-480HX, TS-570S, TS-690S,
TS-850S, TS-870S, TS-2000, and any Kenwood radio that supports the Kenwood AT-300 tuner.
Push and hold the radio’s [AT TUNE] button for one second to start the tuning process. Push the [AT
TUNE] quickly to bypass the tuner or to cancel tuning in progress.
Note: The TS-480HX will automatically reduce its TX power to 100 watts maximum (25 watts
AM) when the radio interface is used.
Pin 1 (Ground) connects to pin of Radio Interface Plug.
Pin 2 (TT) connects to pin 6 of Radio Interface Plu
Pin (Ground) connects to pin 5 of Radio Interface Plug.
Pin 5 (TS) connects to pin 8 of Radio Interface Plug.
g.
3
Pin 4 is not connected.
Pin 6 (+13.8V) connects to pins 2 and 3 of Radio Interface Plug.
4
13 2
465
Kenwood
Rear Panel View 1
2
3
4
5
6
Figure 8. Kenwood Interface Cable.
The MFJ-5114Y interface provides power and control between a Yaesu radio and the MFJ automatic
tuner. Supported Yaesu radios are FT-100, FT-817, FT-857, FT-897, and any Yaesu radio with
compatible CAT system. Push the [TUNE] button on the tuner for 0.5 to 2 seconds to start the tuning
process.
Important: The +13.8 volts connection on the FT-817’s CAT port cannot supply 750 mA of
current needed by the MFJ-928. So remove jumper JP1 located in front of the
Radio Interface jack, and use a separate DC power supply to power the MFJ-928.
(TX INH) connects to pin 7 of Radio Interface Plug.
(SENSE) connects to pin 5 of Radio Interface Plug.
g.
RX
Pin 8 (+13.8V) connects to pin 3 of Radio Interface Plug.
Pin 2 is not connected.
Pin 3
Pin 4 (TX) connects to pin 6 of Radio Interface Plu
Pin 5 ( ) connects to pin 8 of Radio Interface Plug.
Pin 6 (Ground) connects to pin 4 of Radio Interface Plug.
Pin 7 is not connected.
Pin 1
123
456
78
Yaesu
Rear Panel View
1
2
3
4
5
6
7
8
Figure 9. Yaesu Interface Cable (FT-100, FT-817, FT-857, FT-897).

MFJ-928 Compact IntelliTuner Automatic Antenna Tuner Instruction Manual
©2005 MFJ Enterprises, Inc.
9
The MFJ-5114Y2 interface provides control between a Yaesu radio and the MFJ automatic tuner.
Supported Yaesu radios are FT-847 and any Yaesu radio with compatible CAT system. Push the
[TUNE] button on the tuner for 0.5 to 2 seconds to start the tuning process.
Note: The CAT port on the FT-847 does not have a +13.8 volts connection, so a separate DC
power supply must be used to power the MFJ-928.
Pin 1 is not connected.
Pin (TX) connects to pin 6 of Radio Interface Plu
Pin ( ) connects to pin 8 of Radio Interface Plug.
Pin 4 is not connected.
Pin (Ground) connects to pins 4 and of Radio Interface Plug
Pin 6 is not connected.
Pin 7 is not connected.
Pin 8 is not connected.
Pin 9 is not connected.
2g.
3RX
55.
Yaesu
Rear Panel View
11 2345
6789
1
1
2
3
4
5
6
7
8
9
Figure 10. Yaesu Interface Cable (FT-847).
The MFJ-5124Y3 (yes, the MFJ-5124Y3) interface provides power and control between a Yaesu
radio and the MFJ automatic tuner. Supported Yaesu radios are FT-857, FT-897, and any Yaesu
radio that supports the Yaesu FC-30 tuner. Make sure to set jumper JP2 to the “I” position to use the
MFJ-5124Y3. Press and hold in the [A](TUNE) key on the radio for one second to initiate automatic
tuning.
• Transmitter: SO-239 connector for coax cable from transmitter or transceiver. There is a bias tee
connected to this connector so 12 volts DC can be sent down the coax to power the tuner for remote
operation. An optional bias tee DC power injector, the MFJ-4116, is available from MFJ Enterprises,
Inc.
• Antenna 2: SO-239 connector for coax cable from antenna.
• Antenna 1: SO-239 connector for coax cable from antenna. Notice the ANTENNA 1 connector is
internally connected to the WIRE binding post.
Note: To use the ANTENNA 1 connector, make sure to remove the wire antenna, if any, from
the WIRE binding post.
• Ground: Wing-nut terminal for RF ground wire connection.
• Wire: Binding post for connecting single wire antennas. Notice the WIRE binding post is internally
connected to the ANTENNA 1 connector.
Note: To use the WIRE binding post, make sure to remove the antenna, if any, from the
ANTENNA 1 connector.

MFJ-928 Compact IntelliTuner Automatic Antenna Tuner Instruction Manual
©2005 MFJ Enterprises, Inc.
10
Installation
WARNING
●Never operate the tuner with its cover removed. Contact with the components inside the
tuner while transmitting will result in painful RF burns.
●Locate the tuner so that the rear terminals are not accessible during operation. The single
wire connection may have high voltage while transmitting.
●Disconnect all antennas from the tuner during lightning storms.
●Always tune with low power (about 10 watts). Apply maximum power only after tuning up.
●Never exceed tuner specifications.
●Do not transmit with a high SWR for extended periods of time.
1. Place the tuner in a convenient location at the operating position. With a random wire, the feed
through insulators may have high RF voltages. These voltages can cause serious RF burns if the
terminals are touched when transmitting. Be sure to locate the tuner so these terminals cannot
accidentally be contacted during operation.
2. Install the tuner between the transmitter and the antenna. Use a 50-ohm coaxial cable (such as RG-
58) to connect the transmitter (or amplifier) to the connector marked TRANSMITTER on the rear of
the tuner. See Figure 1 on page 3.
3. Connect the antenna(s) to the tuner as follows:
• Coaxial feedlines to the SO-239 connectors labeled ANTENNA 1 and/or ANTENNA 2.
• Random wire or single wire line antennas should be connected to the WIRE binding post on the
back of the tuner. Note the back panel warning: Do not connect WIRE and ANTENNA 1 at
same time! When a single wire antenna is connected it “becomes” ANTENNA 1.
Note: Route all single and random wire antennas safely to prevent RF burn hazard.
4. A GROUND post is provided for an RF ground connection. See “Grounding Hints” on page 13.
5. Connect a 12 to 15 VDC power source to the input jack labeled POWER.

MFJ-928 Compact IntelliTuner Automatic Antenna Tuner Instruction Manual
©2005 MFJ Enterprises, Inc.
11
Miscellaneous
Antenna Memory
The “memory resolution” is the width of frequency spectrum that the tuner recognizes as being the same
as a tuned frequency already in memory. The memory resolution is approximately 0.1 percent of the
lower frequency of each amateur band. For example, the memory resolution on the 40-meter band (7000
to 7300 kHz) is 7 kHz; if the tuner has memorized a setting for 7050 kHz, it will automatically call up this
setting for any frequency from 7047 to 7053 kHz. Memory resolution is smaller at lower frequency to
accommodate the higher antenna Q and larger at higher frequency where the antenna Q is lower. The
memory resolutions for the HF amateur bands 160 through 10 meters are:
Meter Frequency Range (kHz) Memory Resolution (kHz)
160 1800 – 2000 2
75/80 3500 – 4000 4
60 5330.5, 5346.5, 5366.5, 5371.5 and 5403.5 5 memory locations
40 7000 – 7300 7
30 10100 – 10150 10
20 14000 – 14350 14
17 18068 – 18168 18
15 21000 – 21450 21
12 24890 – 24990 25
10 28000 – 29700 28
Table 2. Memory Resolution.
The memory resolution for non-amateur frequency bands between 160 and 10 meters is approximately
0.2 percent of the lower frequency of each band. There are over 2500 memory locations for each memory
bank, and each of the two antennas has four memory banks (A-D). Tuner settings are stored in memory
separately for Antenna 1 and Antenna 2 (settings for single-wire antenna are stored as Antenna 1). This
provides memory for up to eight different antennas. See “ANT Button” on page 5. Defaults are memory
banks 1A and 2A ON.
IntelliTuneTM Algorithm
When the tuner cannot find an appropriate setting in its memory, it begins its calculation function. It
measures the complex impedance of the antenna (load) at the transmitting frequency, then it calculates the
LC components needed for a match. Then it fine-tunes the components for minimum SWR. If for any
reason the tuner cannot calculate the load impedance, it proceeds to yet another method of calculation.
LC Limits
The upper limits of inductance (L) and capacitance (C) are factory-limited according to frequency and
maximum power rating; i.e., higher frequencies need less inductance and less capacitance when the L-
network is properly tuned. These limits are built into the MFJ-928 to prevent matching of extreme load
impedance outside the tuner’s specification, which may result in excess voltage and/or current across the
tuner’s components.

MFJ-928 Compact IntelliTuner Automatic Antenna Tuner Instruction Manual
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Morse Code and Beeps
If not enough power is applied for tuning (less than two watts), “QRO” (dah-dah-di-dah di-dah-dit dah-
dah-dah) will be sent on CW. Increasing the input power above two watts ends this message.
When input power is too high, the tuner enters a self-protection mode. The tuner will not allow any of its
relays to change. This feature is to prevent damage to your tuner.
If too much power is applied when tuning, the tuner will cease the tuning routine and send “QRP” (dah-
dah-di-dah di-dah-dit di-dah-dah-dit) on CW. This occurs when the forward power exceeds 75 watts and
the SWR is greater than 3.0, or when the forward power exceeds 125 watts regardless of the SWR.
If more than 200 watts is applied to the tuner, the tuner will go into bypass mode and send “QRT” (dah-
dah-di-dah di-dah-dit dah) on CW.
If the tuning process is activated under these conditions, the tuner will not start the tuning. It will send
the appropriate code on CW.
The following table shows the various tuner beeps:
Function Indicates By
One Beep Indicates By Two Beeps By Pressing
Antenna 1 2 [ANT] < 1 second
Memory Bank Bank A
(1 beep)
Bank B
(2 beeps)
Bank C
(3 beeps)
Bank D
(4 beeps)
Off
(5 beeps) [ANT] > 1 second
Bypass Toggle Bypass Mode
(L = 0 and C = 0) Restore Last L/C Setting [TUNE] < 0.5 sec.
Tuned SWR SWR ≤1.5
(1 beep)
SWR ≤2.0
(2 beeps)
SWR ≤2.5
(3 beeps)
SWR ≤3.0
(4 beeps)
SWR >3.0
(“SWR”)
[TUNE] for
0.5 to 2 seconds
StickyTune On Off [TUNE] > 2 seconds
Tuning Mode Automatic Semi-Automatic [TUNE] + [ANT]
Table 3. Tuner Beeps.
Foldback Circuit
Modern transceivers with solid-state finals usually have a foldback circuit to protect the final transistors
from high SWR, which can damage or destroy them. A foldback circuit detects the SWR during transmit
and reduces the output power as the SWR rises above a preset threshold, usually 2:1. The higher the
SWR the lower the power is set to prevent damage.
If your transceiver has a foldback circuit, you can simply key down and tune at any power level from 2 to
100 watts. If your transceiver does not have a foldback circuit, you must manually set the power level to
20 watts or less for tuning. At higher power levels, the reflected power occurred during tuning can
damage your transceiver and causes component arcing which can damage the relays in the tuner.
Check your transceiver owner's manual to see if yours has a foldback circuit.

MFJ-928 Compact IntelliTuner Automatic Antenna Tuner Instruction Manual
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Grounding Hints
To minimize RFI, single wire feedlines (such as used with Windom or longwire antennas) should be kept
away from other wiring. Radiation will be minimized if the single wire feeder runs parallel and
reasonably close to the wire that connects the tuner to the outdoor ground. The antenna feed wire should
be adequately insulated to prevent arcing or accidental contact.
CAUTION
For operator safety, a good outside earth ground or water pipe ground should always be
installed and connected to the case of the MFJ-928. Make certain the safety ground also
connects to the transmitter and other station accessories. A wing-nut post marked GROUND is
provided for ground connections.
For safety, please use good DC and RF grounds. It is particularly important to have a good RF ground
when using a single wire feeder. When using a single wire feeder, the tuner needs something to "push"
against in order to force current into the single wire feedline. 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).
Metal water pipes and ground rods provide good DC and AC safety grounds, but they are often
inadequate for RF grounding because they are single conductors. Ground rods by themselves are almost
useless for dependable RF grounding.
RF grounds work much better when "spread out" over a large area, especially when they employ multiple
connections directly to the equipment ground point. Metal water pipes, heating ducts, and fences may
work (especially if they are connected together with multiple wires), but the best RF grounds are radial
systems or multi-wire counterpoises. Radials and counterpoises provide large, low resistance surfaces for
RF energy.
RF and lightning travel on the surface of conductors. Braided or woven conductors have high surface
resistance to lightning and RF. Ground leads for RF and lightning should have wide smooth surfaces.
Avoid the use of woven or braided conductors in RF and lightning grounds unless the lead needs to be
flexible.
Antenna System Hints
Location
For the best performance, an end-fed longwire wire antenna should be at least one quarter-wavelength
long at the operating frequency. Horizontal dipole antennas should be at least a half-wavelength long and
located as high and clear as possible. While good RF grounds help the signal in almost any transmitting
installation, it is extremely important to have good RF grounds with long wire or other Marconi-style
antennas.
Matching Problems
Most matching problems occur when the antenna system presents an extremely high impedance to the
tuner. When the antenna impedance is much lower than the feedline impedance, an odd quarter-

MFJ-928 Compact IntelliTuner Automatic Antenna Tuner Instruction Manual
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wavelength feedline converts the low antenna impedance to a very high impedance at 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.
Incorrect feedline and antenna lengths can make an otherwise perfect antenna system very difficult or
impossible to tune.
One example where this problem occurs is on 80 meters when an odd quarter-wave (60 to 70 feet) open
wire line is used to feed a half-wave (100 to 140 feet) 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.
A problem also occurs on 40 meters with this same antenna example. The feedline is now a multiple of a
half-wave (60 to 70 feet) and connects to a full-wave high impedance antenna (100 to 140 feet). 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.
This places enormous strain on the balun and the insulation in the tuner, since voltages can reach several
thousand volts. This can cause component arcing and heating.
The 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 a feedline close to a multiple of a half-wave long.
• If this tuner will not "tune" a multi-band antenna, add or subtract 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 matching or feeding any dipole antenna with high impedance open wire lines, keep the
lines around these lengths. [The worst possible line lengths are shown in brackets]:
160 meters dipole: 35-60, 170-195 or 210-235 feet [Avoid 130, 260 ft]
80 meters dipole: 34-40, 90-102 or 160-172 feet [Avoid 66, 135, 190 ft]
40 meters dipole: 42-52, 73-83, 112-123 or 145-155 feet [Avoid 32, 64, 96, 128 ft]
Some slight trimming or adding of feedline may be necessary to accommodate the higher bands.
WARNING
To avoid problems, a dipole antenna should be a full half-wave on the lowest band. On 160
meters, an 80 or 40 meters antenna fed the normal way will be extremely reactive, with only a
few ohms of feedpoint resistance. Trying to load an 80 meters half-wave dipole (or shorter)
antenna on 160 meters can be a disaster for both your signal and the tuner. The best way to
operate 160 meters with an 80 or 40 meters antenna is to load either or both feedline wires (in
parallel) as a longwire. The antenna will act like a “T” antenna worked against station ground.

MFJ-928 Compact IntelliTuner Automatic Antenna Tuner Instruction Manual
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Appendices
POWER-ON OPERATIONS
(Press and hold buttons while turning on the power.)
Press and hold + to start the self test.
POWERTUNE
POWER
Press and hold + then press 1 time to reset factory defaults.
ANT TUNE
POWER
Press and hold + then press 2 times to delete current memory bank.
ANT TUNE
POWER
Press and hold + then press 3 times to perform total reset.
ANT TUNE
POWER
Press and hold + then press 4 times to test the power-down circuitry.
ANT TUNE
POWER
Press and hold + then press 5 times to test the relays.
ANT TUNE
POWER
Press and hold + then press 6 times to calibrate the frequency counter.
ANT TUNE
Press and hold + then press 7 times to calibrate the SWR bridge.
POWERANT TUNE
Press and hold + + to delete current antenna memory.
POWERANTTUNE
For the + operations, not pressing or pressing it more than seven times
will cancel the operation after idling four seconds, beep two times and then resume normal operation.
POWERANT
T
UNE
Figure 11. Power-On Operations.
Resetting the Tuner
Each time the tuner is powered off, the microprocessor saves all memories and configurations to non-
volatile memory ready to be used the next time the unit is turned on again. If the tuner is not working
properly, even on initial power on, try resetting to the factory defaults.
Factory Defaults
The unit is shipped with the following default settings:
• Inductance 0 μH
• Capacitance 0 pF on antenna side
• Antenna 1
• Memory Banks 1A and 2A on †
• Tuning Mode Automatic †
† These settings are stored separately for antennas 1 and 2.
Note: Resetting to factory defaults does not erase the antenna memories.

MFJ-928 Compact IntelliTuner Automatic Antenna Tuner Instruction Manual
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To reset the tuner to these defaults:
1. Turn off the power to the tuner.
2. Press and hold only the [ANT] button while turning the power on. Both LEDs will blink until the
button is released.
3. Within four seconds of releasing [ANT], press the [TUNE] button once.
4. After releasing [TUNE] for four seconds, beep three times and resume normal operation.
WARNING: If the MFJ-928 is behaving weirdly or acting erratic, try resetting the tuner to
factory defaults.
Delete Entire Antenna Memory
To delete an entire antenna memory (all four banks), first select the antenna (1 or 2) that you want to
delete. See “ANT Button” on page 5 for details.
1. Turn off the power to the tuner.
2. Press and hold both the [TUNE] and [ANT] buttons while turning the power on. It takes
approximately three seconds to delete all four memory banks of the current antenna.
3. Beep three times and release the buttons to resume normal operation. Remember that the selected
antenna memory will be lost!
Delete Antenna Memory Bank
To delete an antenna memory bank, first select the antenna (1 or 2) and the memory bank (A, B, C or D)
that you want to delete. See “ANT Button” on page 5 for details.
1. Turn off the power to the tuner.
2. Press and hold only the [ANT] button while turning the power on. Both LEDs will blink until the
button is released.
3. Within four seconds of releasing [ANT], press the [TUNE] button two times.
4. After releasing [TUNE] for four seconds, the current memory bank is deleted.
5. Beep three times and resume normal operation. Remember that the selected antenna memory
bank will be lost! However, if the memory is off, no memory bank is deleted; then beep two
times and resume normal operation.
6. Repeat the above procedure to delete the other memory banks, if desired.
Total Reset
To erase both antenna memories (all eight banks) and reset to factory defaults:
1. Turn off the power to the tuner.
2. Press and hold only the [ANT] button while turning the power on. Both LEDs will blink until the
button is released.
3. Within four seconds of releasing [ANT], press the [TUNE] button three times.
4. After releasing [TUNE] for four seconds, both antenna memories are deleted and factory defaults
are reset. The total reset takes approximately six seconds.
5. Beep three times and resume normal operation. Remember that both antenna memories will be
lost!