MFJ MFJ-784B User manual

MFJ-784B Instruction Manual
i
Contents
Fast Start.............................................................................................................1
Before Reading This Manual.......................................................................iv
Chapter 1 Introduction.....................................................................1-1
Introduction to DSP.........................................................................................1-2
Product Overview.............................................................................................1-3
Block Diagram...................................................................................................1-4
Front Panel Layout...........................................................................................1-5
Back Panel Layout............................................................................................1-6
Filter Specifications.........................................................................................1-7
Unit Specifications............................................................................................1-8
General Specifications...........................................................................1-8
Input/Output Specifications................................................................1-8
Chapter 2 Installation.......................................................................2-1
Back Panel Connections...............................................................................2-2
Basic Connections...........................................................................................2-3
Setting Receive Audio Level (Input Level)......................................2-4
Increasing Headphone Audio Level..................................................2-4
Passing Sidetone..............................................................................................2-5
T/R Connection........................................................................................2-5
CW Sidetone Filter..................................................................................2-6
DSP to TNC Connections..............................................................................2-6
Chapter 3 Operation..........................................................................3-1
Initial Operation..................................................................................................3-2
CW Operation............................................................................................3-3
SSB (and other voice modes) Operation.......................................3-4
Front Panel Description................................................................................3-6
PWR LED.....................................................................................................3-6
Input Level LED..........................................................................................3-6
AGC Button.................................................................................................3-7
Program Button.......................................................................................3-7
Memory Button.........................................................................................3-8
Filters Switch..............................................................................................3-8
Tunable Filters Controls........................................................................3-9
Manual Notch Button.............................................................................3-10

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Auto Notch Button..................................................................................3-11
Noise Reduction Control.......................................................................3-12
Noise Reduction Button........................................................................3-12
Volume Control.........................................................................................3-12
Speaker Button.........................................................................................3-12
DSP Button.................................................................................................3-13
Power Button.............................................................................................3-13
Chapter 4 Advanced Features......................................................4-1
Memory Filters..................................................................................................4-2
Saving Memory Filters...........................................................................4-2
CW Spotting Tone............................................................................................4-4
Measuring Frequency............................................................................4-4
Talk..........................................................................................................................4-5
Talk Operation............................................................................................4-5
Jumper Settings...............................................................................................4-8
Talk Settings...............................................................................................4-8
Auto Notch Aggressiveness...............................................................4-8
Normal Jumper Settings......................................................................4-8
Normal Jumper Settings Chart................................................4-9
Setting the CW Sidetone Filter..........................................................4-10
Pre-Set Filters............................................................................................4-11
Data Mode Jumper Settings Chart........................................4-12
Chapter 5 Filter Description..........................................................5-1
LR/HR Filter [1]................................................................................................5-2
Band-stop Filter.........................................................................................5-3
BP Filter [2].........................................................................................................5-4
2BP Filter [3]......................................................................................................5-5
CW Filter [4].......................................................................................................5-6
CW Sidetone Filter..................................................................................5-6
SSB Filter [5].......................................................................................................5-7
RTTY Filter [6]....................................................................................................5-7
HF PACKET Filter [7].......................................................................................5-7
AMTOR Filter [8]...............................................................................................5-8
PACTOR Filter [9].............................................................................................5-8
SSTV/FAX/WeFAX Filter [10]..................................................................5-8
Manual Notch Filter.........................................................................................5-9
Automatic Notch Filter..................................................................................5-10
Noise Reduction Filter....................................................................................5-10
Limited Filters.....................................................................................................5-11
Overlapped Filters............................................................................................5-12

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Appendix A ..............................................................................................A-1
Self-Test................................................................................................................A-2
In Case of Difficulty...........................................................................................A-4
Technical Assistance......................................................................................A-4
MFJ Pre-wired Cables and Open End Cables......................................A-5
Pre-Set and Memory Filters Settings Chart........................................A-6

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Before Reading This Manual
This manual is divided into two parts. The first part, called Fast Start, is meant
for people who need to know nothing except how to minimally install the unit
and operate it on CW and SSB. The second part, Chapters 1 to 5, is meant
for operators who want or need more information. Detailed description of the
unit and its operation are described in these chapters.
The first chapter is an introduction to DSP and the MFJ-784B. The second
chapter tells about the back panel and how to install the unit with a radio or
TNC. Chapter 3 tells how to operate the unit in CW and SSB and describes
the various controls. Advanced Features, Chapter 4, tells how to use the
special features of the MFJ-784B. The last chapter is a description of the
digital filters used in this unit.
The appendix has two important sections, troubleshooting and technical
assistance. There is also a self-test for the unit's digital circuitry and controls.
Refer to these sections if you should have any problem with your new MFJ-
784B.
Important:
Please read this section to become familiar with the terms
and mechanics used in this manual.
Whenever the manual text discusses a control, jack, or level adjustment, the
name will appear in Bold.
Example: Plug a headphone into the Headphones Out jack for ...
The Memory/Normal Filters button will be referred to simply as the Memory
button throughout this manual.
Definitions for the abbreviations used in this manual are listed below:
LR = Low Reject (Cutoff Frequency)
HR = High Reject (Cutoff Frequency)
f1 = Center or Notch Frequency #1
f2 = Center or Notch Frequency #2
fc = Center Frequency
BW = Bandwidth
FIR = Finite Impulse Response
IIR = Infinite Impulse Response
LMS = Least Mean Square
WPM = Words Per Minute

MFJ-784B Instruction Manual
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MFJ-784B Fast Start
Fast Start 1
Fast Start
Beginners' Installation and Operation
To install and use the MFJ-784B in the simplest way possible, follow the steps
below.
On some steps we give you a choice of CW or SSB. Choose one
throughout this Fast Start section. SSB also works with AM and FM voice.
1. Install the unit. Follow the installation diagram on the facing page.
2. Set the controls as follows:
Control Position Meaning
AGC button: out AGC off
Program button: N/A N/A
Memory/Normal button: out Tunable/Pre-Set
Filters switch:
CW or SSB CW or SSB filter
Tunable Filters left knob: center middle center freq.
Manual Notch button: out manual notch off
Tunable Filters right knob: full counter-clockwise widest bandwidth
Auto Notch button: out auto notch off
Noise Reduction control: full counter-clockwise minimum reduction
Noise Reduction button: out noise reduction off
Volume control: full counter-clockwise minimum volume
Speaker button: in speaker on
DSP button: out DSP bypassed
Power button: out MFJ-784B off
3. Apply external power and press and lock the DSP's Power button. The
PWR LED on the front panel should light red. If it is green, press the
Memory/Normal Filters button.
4. Set the input level.
a. Tune your radio to a
CW or SSB station.
b. Set your
radio's volume control to a normal level.
c. Use a screwdriver to adjust the Receive Audio Adjust (on the back
panel of the DSP) until the Input Level LED (front panel) flashes mostly
green and never red (red is too high, off is too low).

MFJ-784B Fast Start
Fast Start 2
5. How to operate the CW filter. (If you work SSB skip to step 6)
a. Your radio should still be tuned to a CW station and setup as in step
2 (except Power). Press and lock the DSP button. Adjust the DSP's
volume control.
b. Press and hold the red Program button. You will hear a "spotting"
tone at the center frequency of the CW filter.
c. Adjust the left Tunable Filters control (center frequency or fc) until
the tone is the same pitch as the CW station. When the tones are
closely matched, release the Program button.
d. Slowly adjust the right Tunable Filters control (bandwidth or BW)
clockwise. The CW station's signal should become clearer (less noise
and QRM).
e. With practice, you will be able to tune in signals without using the
spotting tone. You will also be able to separate multiple signals and
copy signals that were undetectable without the filter.
f. Experiment with the Noise Reduction, AGC, and Manual Notch
controls.
6. How to operate the SSB filter. (If you work CW skip to step 7)
a. Your radio should still be tuned to a SSB station and setup as in step
2 (except Power). Press and lock the DSP button. Adjust the DSP's
volume control.
b. Adjust the right Tunable Filters control (bandwidth or BW) clockwise
to make the SSB signal clearer (less noise and QRM) while not
making the signal less intelligible.
c. Adjust the left Tunable Filters control (center frequency or fc) to peak
the signal for maximum intelligibility.
d. Re-adjust the right Tunable Filters control (bandwidth or BW)
clockwise to eliminate most of the noise and QRM. At some point
decreasing the bandwidth will make the signal less intelligible.
e. Press the DSP button to the "out" position. Find another station that
has CW or some other tone interference audible with a SSB or voice
signal.
f. Press the DSP button to the "in" position and filter the voice signal.
Lock the Auto Notch button "in." Any remaining tones should
disappear or be greatly reduced.
g. Experiment with different filter adjustments and functions under
various conditions to become familiar with the various controls.
7. Now that you have used the DSP filter you can read other parts of this
manual to learn to use the other features of the MFJ-784B.

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Introduction
Contents of This Chapter
>Introduction to DSP Page 1-2
>Product Overview Page 1-3
>BlockDiagram Page1-4
>Front Panel Layout Page 1-5
>Back Panel Layout Page 1-6
>Filter Specifications Page 1-7
>Unit Specifications Page 1-8
General Specifications Page 1-8
Input/Output Specifications Page 1-8

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Introduction to DSP
The MFJ-784B
tunable DSP Filteruses state-of-the-art Digital Signal
Processing (DSP) technology. Digital Signal Processing greatly improves signal
clarity by reducing or eliminating noise (QRN) and interference (QRM). DSP
technology has existed for many years but has always been very complicated
and expensive. Recent advances in integrated circuits have greatly increased
the processing power and reduced the size of DSP units. These same
advances also lowered the cost of DSP filtering, making DSP technology
affordable for the average amateur or short wave listener.
The heart of any DSP system is the digital signal processor. Almost any
microprocessor can perform DSP, such as the one in a personal computer,
but only very fast or special-function processors perform DSP in
real time . A
digital signal processor's commands are tailored to the type of instructions
used in signal processing. The use of special DSP commands allows a DSP
filter function to be completed in very few clock cycles (usually one). The CPU
in a typical personal computer would require a long set of instructions and
therefore many clock cycles to perform the same function. Analog Device's
16-bit 12 MHz processor, the ADSP-2105, is used in the MFJ-784B.
The MFJ-784B DSP Filter converts the analog audio signals from your
receiver to digital information. This conversion is achieved by sampling the
audio signal many thousands of times per second with an analog-to-digital
converter. The result is a string of digital "numbers" that represent the
amplitude and frequency of the analog input signal. The ADSP-2105 chip then
processes the digital information with different digital filter algorithms
depending on the settings of the front panel controls. The end result is a
digitized signal with undesired signal components either reduced or removed
and desired components enhanced. The processed digital signal information
is converted back to an audio signal by a digital-to-analog converter and sent to
the audio amplifier and line level outputs.

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Product Overview
The MFJ-784B tunable DSP filter is a highly selective audio filter suitable for
most amateur applications. The MFJ-784B contains 5 tunable filters, 5 pre-
set filters, a tunable manual notch, an automatic notch filter, and an adaptive
noise reduction filter. Filter settings can be saved into one of ten memory filter
positions.
The 5 tunable filters consist of the following:
LR/HR Low Reject/High Reject
BP Band-pass
2BP Double band-pass
CW CW mode band-pass
SSB SSB mode band-pass
The 5 pre-set data filters are band-pass filters programmed with jumpers for
the different data modes mark-space frequencies and baud rates:
RTTY
HF PACKET
AMTOR
PACTOR
SSTV/FAX/WeFAX
The tunable manual notch filter attenuates 2 tones manually with the front
panel controls.
The auto notch filter attenuates up to 4 tones automatically. The automatic
notch will attenuate moving or shifting tones. The automatic notch is disabled
in the following modes: CW, RTTY, HF PACKET, AMTOR, PACTOR, and
SSTV/FAX/WeFAX.
The noise reduction filter uses adaptive and manually adjustable algorithms to
provide up to 20 dB noise reduction. The amount of noise reduction is
adjustable with a front panel control.

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Block Diagram

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Front Panel Layout
AGC button: Enables the automatic gain control.
Program button: Press to program memory filters, to talk, or to
activate CW spotting tone.
Memory button: Selects either normal or memory filters.
Filters switch: Selects one of ten normal or memory filters.
PWR LED: Indicates normal (red) or memory (green) filters.
Input Level LED: Indicates input signal level (red too high, off too
low, green is OK).
Tunable Filters left knob: Adjusts tunable filters and manual notch.
Manual Notch button: Enables the manual notch.
Tunable Filters right knob: Adjusts tunable filters and manual notch.
Auto Notch button: Enables the automatic notch.
Noise Reduction knob: Controls the level of noise attenuation.
Noise Reduction button: Enables the noise reduction.
Volume control: Controls the output volume level to speaker
and headphones jacks.
Speaker button: Enables the speaker jack.
DSP button: Enables digital processing of input signal.
Power button: Applies power and places the DSP "in-line".
For an in-depth description of the front panel controls, refer to Chapter 3,
Operation.

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Back Panel Layout
Power: 10-16 Vdc @ .5 amp peak (low "Z " audio load)
Headphones Out: 1/4" stereo or mono phone jack
Speaker Out: 3.5 mm stereo or mono phone jack
Filtered Audio Adjust: screwdriver adjustable potentiometer
Filtered Audio Out: RCA phono jack (~1.5 V P-P @ 600 ohms)
Receive Audio Adjust: screwdriver adjustable potentiometer
Receive Audio In: RCA phono jack
To Radio: 5-pin DIN jack
(TNC xmit audio, ground, PTT, receive audio in, T/R)
To TNC: 5-pin DIN jack
(TNC xmit audio, ground, PTT, filtered audio out)
For an in-depth description of the back panel connections, refer to Chapter
2, Installation.

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Filter Specifications
Filter Left Control Right Control Attenuation7Type8
LR/HR1LR: 200-2200 Hz HR: 1400-3400 Hz 57 dB @ 75 Hz FIR
BP fc: 300-3400 Hz BW: 30-2100 Hz 47 dB @ 60 Hz FIR
2BP2f1: 300-3400 Hz f2: 300-3400 Hz 47 dB @ 60 Hz FIR
CW3fc: 300-1000 Hz BW: 30- 700 Hz 47 dB @ 60 Hz FIR
SSB4fc: 600-1700 Hz BW:1000-2500 Hz 57 dB @ 75 Hz FIR
RTTY Jumper Programmable 47 dB @ 60 Hz FIR
HF PACKET Jumper Programmable 47 dB @ 60 Hz FIR
AMTOR Jumper Programmable 47 dB @ 60 Hz FIR
PACTOR Jumper Programmable 47 dB @ 60 Hz FIR
SSTV/FAX/WeFAX Fixed @1050-1350 Hz and 1450-2350 Hz 45 dB @ 60 Hz FIR
Manual Notch f1: 150-3400 Hz f2: 150-3400 Hz 40 dB @ 95 Hz IIR
Manual Notch (CW mode) f1: 300-1000 Hz f2: 300-1000 Hz 40 dB @ 105 Hz IIR
Multiple Automatic
Notch5Entire freq. range of the received audio Upto 50 dB LMS
Random Noise
Reduction6Entire freq. range of selected band-pass filter Up to 20 dB LMS
Note 1: The LR/HR filter becomes a band-stop filter when LR is adjusted higher than HR or becomes an
all-pass filter when LR is adjusted equal to HR.
Note 2: The 2BP filter uses the bandwidth setting last used in BP filter but allows independent variation of
the two center frequencies.
Note 3: The CW filter has an optional jumper-programmable sidetone filter.
Note 4: The SSB filter has its lower cutoff frequency limitedto 175 Hz.
Note 5: The multiple automatic notch has four jumper-programmable levels of aggressiveness and ables
to eliminate up to four changing tones or heterodynes.
Note 6: The randomnoise reduction has a variable level of noise reduction.
Note 7: All FIR and IIR filter attenuations are calculated in dB @ a distance in Hz outside the passband. All
LMS filter attenuations are dependent on the characteristics of the noise.
Note 8: All FIR filters are linear phase with a 23 mS time delay and have the upper cutoff frequency limited
to 3900 Hz.

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FIR - Finite Impulse Response IIR - Infinite Impulse Response LMS - Least Mean Square

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Unit Specifications
General Specifications
Processor: Analog Devices ADSP-2105. Data width - 16 bits. Clock speed -
12 MHz.
Bypass: The MFJ-784B DSP filter has a direct audio bypass when power
switch is in "off" position.
Input/Output Specifications
Power: The maximum current demand will be less than 500 mA at maximum
volume but will always be more than 175 mA.
Filtered Audio Out: This jack provides approximately 1.5 volts P-P into 600
ohm (or higher) impedance loads. The output voltage of this jack is
dependent on Filtered Audio Adjust.
Receive Audio In: This jack should be driven in a range of 1 to 2.8 volts P-P
when Receive Audio Adjust is set to maximum sensitivity. When
Receive Audio Adjust is set to minimum sensitivity, the DSP requires a
very high input voltage. Input circuit loading is 10 K ohms nominal.
Audio Output: Audio output power is ≈2.5 watts into a 6 ohm load with the
MFJ-1315 power supply. Audio frequency response is from 250 to
3100 Hz (-3 dB).

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2
Installation
Contents of This Chapter
>Back Panel Connections Page 2-2
>Basic Connections Page 2-3
Setting Receive Audio Level (Input Level) Page 2-4
Increasing Headphone Audio Level Page 2-4
>Passing Sidetone Page 2-5
T/R Connection Page 2-5
CW Sidetone Filter Page 2-6
>DSP to TNC Connections Page 2-6

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Back Panel Connections
Power: This connector supplies power to the unit. It connects to a 2.1 mm
coaxial plug with the center conductor positive and the shield ground. An
optional dc supply, the MFJ-1315, is available from MFJ. The voltage
should be 10-16 Vdc.
If the power supply voltage drops below 10 volts
the MFJ-784B will perform erratically.
Warning:
V oltages greater than 18 volts or reverse polarity may
permanently damage the MFJ-784B.
Headphones Out: This jack supplies volume controlled audio for headphones. It
accepts standard male 1/4 inch stereo or mono phone plugs and
provides audio to both stereo and mono headphones.
Speaker Out: This jack supplies volume controlled audio for a speaker with a
3.5 mm stereo or mono phone plugs. Disengaging the Speaker button
disables this jack.
Filtered Audio Adjust: This adjustment varies the level of the audio outputs to
Filtered Audio Out and pin 4 of the To TNC port.
Filtered Audio Out: This jack supplies line level audio for tape recorders or
audio amps. It is a standard RCA phono jack. A quality shielded cable
should be used for connections to this jack. The output is dependent on
the Filtered Audio Adjust and independent of the DSP's volume control.
Receive Audio Adjust:This adjustment controls the sensitivity of the Receive
Audio In jack and pin 4 of the To Radio port. Proper adjustment is
achieved if the Input Level indicator flashes mostly green and never red
when the receiver's volume is at normal levels. Refer to page 2-4.
Receive Audio In: This jack is normally connected to the receiver's speaker or
headphones output. It is a standard RCA phono jack. A shielded cable
should be used to connect this connector to the station receiver.
To Radio:This port supplies connections for transmit and receive audio. PTT is
connected directly to the To TNC port. A connection is also available for
a T/R line to automatically bypass the filter during transmit.
To TNC:This port supplies connections to the filtered audio output and the
transmit audio inputs. PTT is connected directly to the To Radio port.