MFJ Enterprises 9475 Hf Transceiver Instruction Manual

							MFJ-9475 Instruction Manual    75-Meter SSB Travel Radio 
1  Introduction
 
 
Congratulations on choosing the MFJ-9475 75-Meter transceiver.  At home or on the 
road, your MFJ-9475 is built to deliver performance you never thought possible from a 
low-power radio.  Before attempting to operate, please read this manual carefully!  Lets 
begin with an introduction to some special features we think youll like! 
 
•
•• •  Easy to Operate:  A back-to-basics radio, the MFJ-9475 is simple to use.  There are 
no complex microprocessor functions to master, and youll be on the air in minutes! 
 
•
•• •  Great Receiver Performance:  Your radio features a quiet DBM (doubly-balanced 
mixer) front-end and carefully-distributed gain.  If the signal is there, youll hear it.  If 
the signal isnt
 there, you wont hear a lot of other things that shouldnt be there! 
 
•
•• •  Analog S-Meter:  Responsive mechanical meter gives accurate meaningful reports. 
 
•
•• •  Excellent Selectivity:  Sharp ladder filter cuts adjacent chatter and focuses transmitter 
power where you need it most. 
 
•
•• •  Smooth, Stable VFO:  Effortless tuning with custom-manufactured 8:1 reduction-
drive ball-bearing VFO tuning capacitor. 
 
•
•• •  Powerful AF Output:  Big audio--even on the road--from a special Philips BTL audio 
chip and rugged 3 speaker. 
 
•
•• • Full-time RF Speech Processing:  Commanding speech cuts through QRM.  
Compare it with your 100-Watt rig--youll be amazed
 by the signal reports. 
 
•
•• •  Travel Light:  Packs a heavy punch without the heavy power supply!  Designed to run 
on NiCads or the ultra-light MFJ-4110 AC wall-adapter supply. 
 
•
•• • Rugged PA:  Bullet-proof final runs cool, tolerates accidental shorts and opens. 
 
•
•• •  Made to Last:  Conservative design, premium plate-through pc board, quality 
components, handsome brushed-aluminum panel, and a tough vinyl-clad case ensure 
years of dependable service. 
 
Youll enjoy countless hours operating the MFJ-9475.  If anything goes wrong, its fully 
backed by MFJs exclusive No Matter What 1-year guarantee.  If it breaks, well take 
care of it! 
 
Note:  Due to bandwidth considerations, no CW adapter is offered for the MFJ-9475.   
						

							MFJ-9475 Instruction Manual    75-Meter SSB Travel Radio 
2  MFJ-9475 Control Locations and Functions
 
 
 
 
                                 
Mic GainPowerAntenna+ -
12
3 
 
Rear Panel 
 
 1. Power Jack: 5.5 mm OD x 2.1 mm ID, (+) to center pin. 
 2. Antenna Jack: SO-239 for standard coax plug. 
 3. Mic Gain:   Controls speech-amp gain--normal setting 12:00. 
  
 
 
 
 
 
                      
On
OffOn
Off
Mic
Power TuneXmitVolume
Pwr
MFJ 75-Meter SSB Radio
Model MFJ-9475
1
2
3456
7
84.0 3.753.953.93.85
3.8
  
 
Front Panel 
 
 1. Meter:   Shows signal strength on RX, ALC Voltage on TX. 
 2. Power Switch: Turns on power to the transceiver. 
 3. Mic Connector: 5-pin DIN connector for 600Ω dynamic microphone. 
 4. Tune Switch: Injects carrier for antenna tuner or other adjustments. 
 5. Xmit LED: Illuminates when unit is transmitting. 
 6. Tuning Dial: VFO control for tuning in stations. 
 7. Volume Control: Adjusts speaker volume to a comfortable listening level. 
 8. Pwr LED: Illuminates when power is turned on.  
						

							MFJ-9475 Instruction Manual    75-Meter SSB Travel Radio 
3  Assembling Your Station
 
 
Youll need three items to put your MFJ-9475 on the air: 
 
Power Supply:  The MFJ-4114 AC/NiCad Portable Power Pack or MFJ-4110 AC. Wall-
adapter Supply are especially designed for the MFJ-9475.  You may also use any other 
regulated 13.8-Volt supply or 10-cell NiCad pack that delivers 2 Amps on peaks (RF 
output slightly lower with 12-volt supplies).  Use a 5.5 mm OD x 2.1 mm coaxial-type 
power plug (Radio Shack 274-1567) with (+) connected to the center pin. 
 
Microphone:  The MFJ-9475 speech processor was designed around our companion 
MFJ-290 600Ω Dynamic Microphone.  However, you may use any low-Z dynamic 
microphone with a switched cartridge and PTT line by installing a 5-pin DIN connector 
(Radio Shack 274-003 or equivalent), as shown below: 
 
            
Pin 3:  PTT Line
Pin 4:  Mic Line
Pin 1,2,5:  Ground1
4
253Mic (#4)
PTT (#3)
Gnd (#1,2,5)
 
 
Antenna:  The MFJ-9475 works with any 75-Meter 50Ω antenna exhibiting low VSWR 
(2:1 or less is considered acceptable for amateur radio service).  Avoid antennas with 
unknown or high VSWR.  
See page 5 for more detailed 75-meter antenna suggestions. 
 
 
Setting up Your Station
 
 
The MFJ-9475 is small in size, allowing you to set up an amateur radio station in nearly 
any location.  The better the operating environment, the better your radio will perform.  
Find a space that is sheltered, dry, and dust free.  Avoid surfaces that are exposed to direct 
sunlight, strong magnetic fields, rapid temperature changes, or high ambient noise levels.  
Connect your transceiver to a good earth ground, if available. 
 
 
Antenna
Power Supply
(MFJ-4110 Shown)
Mic
+
5.5 mm OD
2.1 mm ID Power Plug
MFJ-290 or Equivelent 2A @ 13.8V--or any
Regulated
Source (50-Ohm)
600-Ohm Dynamic
 
 
  
						

							MFJ-9475 Instruction Manual    75-Meter SSB Travel Radio 
4  Operating Your MFJ-9475
 
 
 
                
On
OffOn
Off
Mic
Power TuneXmitVolume
Pwr
MFJ 75-Meter SSB Radio
Model MFJ-9475
4.0
3.75 3.9 3.85
3.8 3.95
 
 
Receiving:  The MFJ-9475 is extremely simple to operate.  To get started, press the 
POWER
 switch on (the green PWR 
LED should illuminate).  Adjust the VOLUME
 control 
for a comfortable listening level.  Now, tune in your station with the VFO TUNING
 knob.  
Thats all there is to it!  
 
Antenna Tuners:  If you are using a tuner, adjust controls for the strongest received 
signal first--before keying the transmitter.  This will bring antenna VSWR into the 
ballpark.  For final adjustment, press the radios TUNE 
switch to ON.  
This will 
generate a steady carrier (the red XMIT 
LED should light).  Be sure to follow the tuner 
manufacturers procedures when adjusting for minimum VSWR.    
 
Before You Transmit:  Your radios VFO dial was calibrated at the factory.  However, 
under FCC rules, you are solely responsible for the operating frequency of your 
transmitter (MFJ is not).  If you have doubts concerning the dials accuracy, check it out  
against a radio with a digital frequency readout before operating near the band edges.  
Also, know where the sub-band margins are for your particular class of license.     
 
Transmitting:  Press the PTT switch and speak normally while holding the microphone 
1-2 inches away (the red XMIT 
LED should light).  The radios S-meter should deflect 
about 1/2 scale as you speak.  Resist the temptation to yell or close-talk.  The speech 
processor is designed to automatically re-adjust gain for each syllable.  Over-driving the 
radios speech amplifier circuitry will detract from its performance.  As you speak, note 
that the S-meter is indicating ALC voltage--not RF output power.  Speaking loudly to 
push the meter higher will have no benefit.  
 
Antenna VSWR:  Always check VSWR before using a new or questionable antenna.  
Highly reactive loads will affect ALC meter readings during transmit, making them 
appear  abnormally high or low, depending upon the nature of the mismatch.  In extreme 
cases, highly-reactive loads can cause the transmitter to emit spurious out-of-band signals 
in violation of FCC rules.  If you notice that your ALC voltage is swinging excessively 
high or low, consider this a wake-up call to check the condition of your antenna!   
 
  
						

							MFJ-9475 Instruction Manual    75-Meter SSB Travel Radio 
5  Antennas for your MFJ-9475
 
 
 
 
1/2-wave Dipole
or Inverted-VDipole Length  =  Freq in MHz /468
Inverted-V Length =  Freq in MHz /492
Install balun here
 
 
 
 
The key to success when operating low-power SSB is a properly-installed full-sized 
resonant antenna.  Dipoles and inverted-Vs generally work best for regional coverage. 
 
Typical length for a 75-meter phone-band dipole is around 121 feet.  This length may 
vary somewhat, depending upon antenna height, ground conditions, etc. 
 
For restricted-space installations, inductively-loaded dipoles deliver nearly equal on-air 
performance--but with a sacrifice in bandwidth.  If you shorten your dipole with loading 
coils, use high-Q inductor stock (Q = 300 or better for minimum loss) and install them at 
the center of each antenna leg. 
 
Regardless of type, always mount your antenna as high and in-the-clear as possible.  For 
flat dipoles, best VSWR typically occurs at 40-70 feet AGL.  A single dipole will not 
cover the entire 75/80 band at low VSWR, but if you cut for resonance just below 3.9 
MHz, VSWR should remain acceptable at both phone-band edges.  Alternatively, cut for 
the center of your alotted sub-band or favorite rag-chewing frequency. 
 
Feedline loss is usually not a critical consideration at 3.9 MHz, and any light-weight 50-Ω 
cable such as RG-8X or RG-58 will work fine.  A simple choke-balun can reduce feedline 
interaction when coax does not drop perpendicular to the flat-top.  Use a commercial 
balun, or simply coil 25 feet of feedline and tape in place just beneath the center block for 
an inexpensive solution.  Make sure all connectors and joints are clean, properly soldered, 
and protected from moisture.  Avoid water-proofing methods that can trap moisture or 
condensation inside connectors. 
 
For alternative antenna designs, see The ARRL Antenna Book
 or ARRL
 Antenna 
Compendium
 for descriptions and construction details.  If possible, avoid compromise or 
multiband designs. 
 
  
						

							MFJ-9475 Instruction Manual    75-Meter SSB Travel Radio 
6  Typical Technical Specifications
 
 
Receiver Section: 
  Frequency Coverage    3750 - 4000 kHz  
 Receiver Type   Single-conversion Superhet 
  VFO Frequency    6.0 - 6.250 MHz     
 IF Frequency   10 MHz 
  IF Selectivity      -6 dB @ 2.4 kHz 
  Blocking Dynamic Range   >100 dB  
 Sensitivity   0.3-uV MDS 
  Audio Output      0.75 Watts into 8Ω at 10% THD 
 Receive Current  100 mA 
 
 
Transmitter Section: 
 RF Power Output    12-Watts PEP (10-Watts average speech) 
 Suppression   45 dB  
 VSWR Tolerance:  3:1 VSWR 
  Maximum Current     2.2 Amps at 13.8 VDC 
 Speech Enhancement  Syllabic RF-compression 
  Transmit Current    2.0 Amps @13.8 VDC 
 
Block Diagram
 
 
    
RX BPF
L1-L2RX MXR
VFOU1
SSB FilterIF Amp
U2Prod Det
BFOU3AF Amp
U4A
Sw Q5
AGC
Q2-Q4
Vol
AF Pwr
U5
MBuff
Q1
Sw Q6
Sw Q8Sw Q7
Mic Amp
U4BBal Mod
U6Tx Mxr
U7TX BPF
L5-L6Pre-Drv
Q9Driver
Q10
PA
Q11
LPF
PTTK1
Det
 
 
  
						

							MFJ-9475 Instruction Manual    75-Meter SSB Travel Radio 
7  Theory of Operation
  (see Block Diagram) 
 
Receiver:  A four-pole bandpass filter at L1-L2 pre-selects incoming 4-MHz signals.  
Active mixer U1 amplifies and converts signals to 10-MHz using a self-generated 6.0-
6.25 MHz VFO signal.  Crystal ladder SSB filter Y1-Y6 sets message-channel bandwidth 
at approximately 2.4 kHz.  Diode switching routes signals through the SSB filter and IF 
amplifier U2.  U2 provides AGC-controlled IF gain in RX mode, and syllabic-rate RF-
compression in TX mode.  DC amplifier Q3/Q4 drives the AGC port of U2--plus the S-
meter circuit.  In RX mode, AGC is audio-derived from AF pre-amp U4A.  Switch Q2 
sets slow AGC rate for SSB reception.  In TX mode, AGC control voltage is derived from 
PA level detector D9, and switch Q2 sets a fast AGC time constant for processing.  In RX 
mode, U2 feeds receiver product detector U3 through switch D3,D4.  U3 demodulates 
incoming SSB signals, using a self-generated 10-MHz LO signal.  U3s audio port feeds 
AF preamp U4A, which boosts and actively-filters the recovered AF signal for HF noise.  
Input to U4A is killed in TX mode by switch Q5 to disable the AF AGC path to U2.  
U4A drives AGC detector D6,D7--and drives AF power amplifier U5 through the radios 
volume control.  U5 powers the speaker during RX mode, and is gated off via the logic-
level kill pin in TX mode. 
 
Transmitter:  Microphone speech amp U4B drives balanced modulator U6 during TX 
mode.  Switch Q6 kills U4 output in RX mode to prevent mic bleed-through into the IF.  
LO for U6 is derived from U3s on-board BFO oscillator.  FET Switch Q8 is used to 
unbalance U6 for full carrier generation (for tune-up).  DSB output from U6 is routed 
through ladder filter Y1-Y6 via switch D1,D2 to remove USB products and carrier 
artifact.  After undergoing dynamic compression in U2, the processed LSB signal is 
routed to transmit mixer U7 via switch D3,D4.  U7 mixes 10-MHz LSB with VFO energy 
to generate RF output (the VFO signal is buffered prior to mixing by source-follower 
Q1).  Band-pass filter L5,L6 selects the desired mixer product (4 MHz), and suppresses 
other mixer products.  FET pre-driver Q9, which functions as impedance-matching device 
and amplifier, provides a high-Z load to the BPF for higher filter Q.  Lo-Z output is then 
fed to broad-band driver Q10.  Q10 drives PA stage Q11, a single-ended un-tuned linear 
amplifier.  Bias for class AB operation is generated by clamping diode D10.  T5 matches 
PA output into a 50Ω low-pass harmonic filter at L7,L8.  Level detector D9 tracks RF 
amplitude of the speech envelope, and generates a DC feedback voltage to drive AGC 
amplifier Q3,Q4 for control of U2 gain (speech processing). 
 
Switching and Regulation:  Q7 activates relay K1, which--in turn--routes the antenna 
line and activates the +T and +R buses in the radio.  The +T and +R buses are used to 
power some low-level stages, as well as key several switch nodes and bias Q11 on during 
TX mode.  Adjustable regulator U8 sets Vcc for most low-level stages.  Fixed regulator 
U9 hardens U1 operating voltage to ensure VFO stability.  Crowbar diode D11 and a pc-
track fuse protect the radio from reverse polarity. 
  
						

							MFJ-9475 Instruction Manual    75-Meter SSB Travel Radio 
8  Troubleshooting
 
 
Radio Does Not Power Up:  Check the power plug, supply wires, and power source.  
Also, check to see if the REVERSE-POLARITY FUSE
 is open inside the radio.  This 
fuse is etched onto the pc board next to the radios power jack.  If open, replace with a 
2.5-A pigtail type fuse or short length of #36 enamel wire.    
 
No Signals Received:  Check the antenna and feedline.  Is the TUNE
 switch stuck on?  Is 
the band dead?? 
 
Does Not Transmit:  Check the microphone PTT switch, cable, and connector.  Check 
your power source to see if enough current is available to transmit. 
 
Erratic Transmit:  Check to see if VSWR is above 3:1.  Also, is the voltage of your 
power source low or soft under full load? 
 
Receiver Motorboats (low-frequency oscillation) on 12-V battery: Regulator voltage 
set too high.  Reset R64 for 10.0 Volts at TP1.  Set AGC voltage (R6) for 4.3 Volts at 
TP2 and re-zero Meter Zero trimpot (R51).   
 
VFO Drifts in Frequency:  Is the radio sitting in direct sun-light, on a hot surface, or in 
a cold draft?  Was it recently moved from a very cold to a warm area (condensation)? 
 
Poor Carrier Suppression:  Was the radio exposed to rough-handling or shock?  To 
null, turn MIC GAIN
 down and adjust R36 and T3 for minimum carrier. 
 
Low Transmit Audio:  Is the microphone a 600Ω dynamic type?  Is the MIC GAIN
 set 
too low? 
 
Noise on Transmit Audio:  Is the MIC GAIN
 set too high in a noisy room?  Is the 
microphone or radio positioned next to a motor or large power transformer?  
 
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 or the MFJ Factory
 at 
601-323-5869.  You will be best helped if you 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 FAX 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. 
  
						

							MFJ-9475 Instruction Manual    75-Meter SSB Travel Radio 
9  Field Alignment Procedures for the MFJ-9475 Transceiver
 
 
These internal adjustments require technical competence and access to accurate lab-type 
test equipment.  If you dont feel qualified to perform these procedures, please let MFJ--or 
a qualified radio service technician--do the work.  Mis-alignment could result in out-of-
band spurious emission (in violation of FCC rules) and poor on-air performance. 
 
Special Tools, Parts, Test Equipment: 
 AC Power Supply, 13.8 Volts @ 2 Amps 
 Voltmeter 
  Non-inductive Alignment tool Kit 
 Frequency Counter 
  Watt meter with 50Ω Dummy Load 
 4-MHz Signal Generator or Other Signal Source 
  75-Meter Receiver  
 
Initial Test Set-up: 
[  ]  Remove transceiver cover. 
[  ]  Connect 13.8-V power source to radios Power Jack  
[  ]  Connect Microphone. 
[  ]  Turn on unit. 
 
Voltage Checks and Adjustments: (Use Voltmeter) 
[  ]  Set Voltage Regulator for 10.2 Volts at TP1 via R64. 
[  ]  Set Receiver AGC for 4.3 Volts at TP2 via R6. 
[  ]  Set S-meter pointer to 0 via R51.  
 
VFO Calibration:  (Use Counter, Dummy Load) 
[  ]  Tune VFO dial to mid-band (3.9 MHz), and connect dummy load. 
[  ]  Place counter pickup lead near (but not touching) wire from pc board to antenna jack. 
[  ]   Press TUNE
 and adjust L3 for 3.900 MHz reading on counter.* 
*(or connect a counter to U7 pin 6 and adjust L3 for a 6.103 MHz readout)  
 
BFO Frequency Check and Alignment:  (Signal Generator, AF Osc or Counter) 
[  ]  Tune across 3.900 Mhz signal, identifying peaks in passband on S-meter. 
[  ]  Carefully set VFO dial to lowest-pitched response peak (listen to heterodyne note).  
[  ]  Adjust BFO trimcap (C61) until CW note is 600 Hz * 
[  ]  Recheck to confirm that the 1st peak
 is at 600 Hz and that receiver mode is LSB. 
* (Use an audible 600-Hz reference tone, or connect AF-range counter to U4 pin 7). 
 
Carrier Null:  (Use a second receiver to monitor residual carrier) 
[  ]  Tune MIC GAIN 
full off (counter-clockwise). 
[  ]  Key the microphone and monitor residual carrier with second receiver. 
[  ]  Adjust R36 and T3 (alternately) for minimum carrier. 
  
						

							MFJ-9475 Instruction Manual    75-Meter SSB Travel Radio 
10  Receiver Sensitivity: (Use a calibrated RF-Signal Generator) 
[  ]  Connect a weak 3.900 signal source to ANTENNA 
jack. 
[  ]  Tune in source for maximum S-meter reading using VFO. 
[  ]  Adjust Signal Generator amplitude for S5-S7 meter reading. 
[  ]  Touch up L1, L2, T1, T2 for maximum S-meter reading. 
 
Transmitter Bandpass Filter Alignment: (Use a Watt meter and Dummy Load) 
[  ]  Connect low-power watt meter with dummy-load to the ANTENNA
 jack. 
[  ]  Turn R61 fully clockwise to disable the transmitters ALC detector. 
[  ]  Press TUNE
, carefully touch up L5, L6 for maximum power output on watt meter. 
 
PA Bias Adjust:  (Use the uA function on a Voltmeter) 
[  ]  Turn MIC GAIN 
fully off (CCW). 
[  ]  Connect uA meter across the PA-BIAS 
test points located at RFC6 (see below). 
[  ]  Key Mic and adjust Bias Pot R66 for a 50-uA reading on the test meter. 
 
Speech Processor Adjustment: 
[  ]  Set the radios MIC GAIN 
control to fully open (clockwise). 
[  ]  Press PTT switch and speak into the microphone--2 inches away, normal voice. 
[  ]  Adjust R61 for mid-scale meter readings on peaks (re-set MIC GAIN 
when done). 
 
Internal Adjustment Locations: 
 
               
VFO
TuneTune
MicMic Gain
BFO (C61)
L1
L2Receiver 
Bandpass Filter T2
T1
L3T3 Carrier Balance
R36
L6
L5 Transmitter
Bandpass FilterVFO
Calibrate
AGC
R6
TP2
TP1
Bal Mod
Vol Ant
Speech
Proc
R61
R64 V. Reg
Meter Zero
R51
PA
Bias
R66
IF Amplifier
Test Points
PowerRFC6
FusePwr
Jack
PA Bias
+(10.2 V)
(4.3V) (50 uA)