MFJ 9420 User Guide
Congratulations on your choice of the MFJ-9420 20-Meter transceiver. The MFJ-9420 is specially designed
to deliver performance you never thought possible from a low power radio. Please read this manual car efully
before attempting to operate your new radio.
FEATURES
The MFJ-9420 is an easy-to-operate,"back to basics" radio. Operate the unit with ease in minutes!
Quiet DBM front end and lots of overall gain for great sensitivity. If the signal is there, you'll hear it!
Adjust the tuner or aim the beam with pin-point accuracy. A calibrated analog S meter measures even the
smallest variations in signal strength. The meter also monitors your speech processing level on transmit.
Sharp ladder filter cuts adjacent chatter and focuses transmitter power where you need it most for great
selectivity.
Effortless tuning with custom manufactured 8:1 reduction drive ball bearing VFO tuning capacitor provides
smooth and stable VFO.
Big audio and powerful AF output even in noisy locations from a special Philips BTL audio chip and
rugged 3" sp eaker.
Full time RF speech processing commands speech cuts through QRM and competes with radios r unning
far more power. Compare with your 100-watt rig. You'll be amazed by the signal reports!
Packs the same punch as 50-Watt radios without the heavy 10 Amp power supply! Designed to run on
NiCd's or the ultra light MFJ 4110 ac wall adapter supply.
Rugged Motorola PA transmitter runs cool, and tolerates 3:1 VSWR accidentally opened feedlines or
feedline shorts.
Conservative design, with a pre mium plate through pc boar d, quality components, handsome brushed
aluminum panel, and a tough vinyl clad case ensure years of dependable service .
Available CW adapter board installs and lets you jump to the low end to work CW.
Semi-break in keying and sid etone.
At home or on the go, you'll enjoy countless hours operating the MFJ-9420. Best of all, it's fully backed by
MFJ's exclusive "No Matter What" 1 year guarantee. If it breaks, we'll take care of it!
You'll need three things to get your MFJ-9420 on the air fast:
12 14 Volt 2 Amp Power Source.
600 Ohm Dynamic PTT Microphone
20 Meter Antenna
1. POWER SUPPLY: The MFJ 4114 AC/NiCd Portable Power Pack or MFJ-4110 ac Wall adapter. Supply
are specially designed to run the MFJ-9420. You may also use any 13.8 Volt supply or 10-cell NiCd pack as
long as it delivers 2 A on peaks (12 Volt supplies will work fine but at reduced RF output). Use a 5.5mm OD
x 2.1mm coaxial type power plug (Radio Shack 274 1567) with (+)connected to the center pin.
2. MICROPHONE: The MFJ 9420 speech processor circuit was designed around the companion MFJ 290
600 Ohm Dynamic Microphone. Radio Shack's 21 1172 replacement microphone also plugs in without
modification and works well. If the mike you select requires a plug, install a 5 Pin DIN connector (Radio
Shack 274 003) as shown:
Pin 3: PTT Line
Pin 4: Mic Line
Pin 1,2,5: Ground
3. ANTENNA: The MFJ 9420 will function with any 20 Meter antenna exhibiting a VSWR of 3:1 or less
(your home station antenna or the MFJ 1772 Portable Dipole should work fine). AVOID USING
ANTENNAS WITH UNKNOWN OR HIGH VSWR. The MFJ 9420 PA is not protected by high VSWR
shutdown circuitry and you may generate out-of-band parasitics if a high VSWR load is present.
IMPORTANT OPERATING NOTES:
Your MFJ 9420 features a very potent speech processor. PLEASE RESIST THE TEMPTATION TO
SHOUT OR "CLOSE TALK" INTO THE MICROPHONE IN ORDER TO BE HEARD! Instead, hold the
mic about 2"away and speak normally. The S Meter should deflect about 1/2 scale as you speak although
this may vary somewhat with antenna load. When oper ating in noisy environments, you may find it
necessary to turn down the mic gain control (a screwdriver adjustment located on back panel) to reduce
background noise.
The MFJ 9420 uses an analog VFO tuning dial which is inherently less accurate than digital readouts (on
the plus side,analog tuning reduces phase noise, lowers power consumption, and saves you money).
Please take the potential for dial error into account when operating near the edge of your authorized sub
band.
RECEIVER SECTION:
Frequency Coverage: 14.150 14.350 MHz (14.000 14.100)*
Receiver Type: Single conversion superhet
VFO Frequency: 4.150 4.350 MHz (4.000 4.100)*
IF Frequency: 10 MHz
IF Selectivity: 6 dB at 2.5 KHz
AGC: Audio derived
Sensitivity: <.5 uV for 12 dB S/N
Audio: >1 Watt into 8 Ohms at 10% THD
Receive Current: 5O 100 mA typical
TRANSMITTER SECTION:
RF Power Output: 10W Average Speech (8 10W CW)*
VSWR Tolerance: 3:1 VSWR
Maximum Current: 2.2 Amps peak at 13.8 Vdc
Audio Enhancement: RF compression processor
* Requires CW adapter module
RECEIVER: Four pole bandpass filter L1 L2 preselects incoming 14 MHz signals. Active mixer U1
amplifies and converts signals to 10 MHz using a self generated 4 MHz VFO signal. Crystal ladder filter
Y1 Y6 sets message channel bandwidth (diode switching routes transmit and receive signals through the filter
and U2). IF amplifier U2 provides AGC controlled IF gain in RX and RF compression speech processing
in transmit.
The dc amplifier Q3/Q4 drives the AGC input of U2 and the S metercircuit. In RX, AGC is audio derived
from AF pre-amp U4a (switchQ2 sets slow AGC decay for SSB reception). On transmit, processor
control voltage is derived from PA level detector D9 (Q2 sets fast decay for syllabic processor).
Receiver product detector U3 demodulates incoming SSB signals(10 MHz LO is self generated by U3).
U3's audio output feeds U4a, a preamp and active LP audio filter. U4a drives ACG detector D6/D7
(input to U4a is killed by switch Q5 during TX to disable the AGC path to U2). U4a also drives AF power
amplifier U5 through the volume control. U5, which powers the speaker during RX , is gated into sta ndby
during TX to prevent residual feed through.
TRANSMITTER: Microphone speech amp U4b drives balance modulator U6 during TX (switch Q6 kills
U4 output to prevent mic bleed through via U 6/U2 during RX). LO for U6 is derived fro m U3's BFO
oscillator. Q8 is used to unbalance U6 for carrier or CW generation. DSB output from U6 is routed to
Y1 Y6 via switch D1/D2 for removal of LSB products and carrier artifacts. After undergoing dynamic
compression in U2, the processed USB signal is routed to transmitter mixer U7 by switch D3/D4 where it is
mixed with 4 MHz VFO (VFO signal is sampled from U1's oscillatorand buffered by Q1). Bandpass
filter L5 L6 selects the 14 MHz mixer product and feeds it to pre-driver Q9. Q9 feeds driverQ10. Q10
drives PA stage Q11. Q11 operates in single-ended class AB with bias generated by clamping diode D10.
T5 matches PA output to a 50 Ohm system, and low pass filter L7 L8 suppresses harmonic content. Level
detector D9 tracks the SSB speech envelope and generates feedback to Q3/Q4 and U2. Syllabic
compression of the speech waveform optimizes average transmitter output power. The MFJ 9420 is
especially designed to operate from light-weight constant current power sources such as NiCd cells or the
MFJ wall adapter AC supply.
SWITCHING AND REGULATION: Q7 activates relay K1, which routes the antenna line and activates
the +T and +R buses (+T and +R buses power some stages, key switch nodes, and bias Q11 on
duringTX). Adjustable regulator U8 sets Vcc for low level stages. Fixed regulator U9 sets U1 operating
voltage to ensure VFO stability. Crowbar diode D11 and a pc track fuse protect the radio from reverse
polarity.
REAR PANEL
1. POWER JACK: 5.5mm OD, 2.1mm ID, (+) to center pin.
2. ANTENNA JACK: SO 239 for standard coax plugs.
3. MIC GAIN: Sets Speech amp Gain (normal setting 12:00).
4. CW ADAPT: Engages CW adapter (accessory).
5. KEY: Accepts straight key or keyer.
FRONT PANEL
1. METER: Show signal strength on RX, ALC on TX.
2. POWER SWITCH: Turns power on to transceiver.
3. MIC: 5 Pin Din Jack for Dynamic Microphone.
4. TUNE: Injects carrier for ATU adjustments.
5. XMIT: LED illuminates when transmitting.
6. TUNING: Tunes in stations, indicates VFO frequency.
7. VOLUME: Adjusts listening level.
8. PWR INDICATOR: LED illuminates when power on.
To put your MFJ 9420 station in operation, you'll need a powersource, a 20 Meter antenna, and a
microphone. He re are somespecific suggestions to hel p you get started:
POWER SOURCE: 12 15 V @ 2A (+) TO CENTER PIN
The MFJ 4114 ac/dc PORTABLE POWER PACK and MFJ 4110 ac WALL ADAPTER SUPPLY are
especially designed for your radio. However,you may use any filtered dc power source capable of
delivering 12 15 volts at 2 Amps (13.8V required for full RF output). The dc power connector at the rear
of your MFJ 9420 is a 5.5mm OD,2.1mm ID coaxial type jack. Extra plugs are available from
RadioShack stores (#274 1567). Always connect plus (+) to the CENTERPIN.
Loading...