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MFJ-784B
User Manual
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MFJ MFJ-784B User Manual

MFJ-784B Instruction Manual
Contents
Fast Start.............................................................................................................1
Before Reading This Manual.......................................................................iv
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
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
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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MFJ-784B Instruction Manual
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
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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MFJ-784B Instruction Manual
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
iii
MFJ-784B Instruction Manual 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 MFJ­784B.
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 Memo ry/Nor mal Filters button will be referred to simply as the Me mory 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
iv
MFJ-784B Instruction Manual
v
MFJ-784B Fast Start
Fast Start
Beginners' Installation and Operation
To install and use the MFJ-784B in the simplest way possible, follow the steps below.
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:
3. Apply external power and press and lock the DSP's Power button. The
4. Set the input level.
On some steps we give you a choice of CW or SSB. Choose one
Control Position Meaning AGC button: out AGC off
Program button: N/A N/A Memory/Normal button: out Tunable/Pre-Set Filters switch: 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
PWR LED on the front panel should light red. If it is green, press the Memory/Normal Filters button.
a. Tune your radio to a b. Set your 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).
radio's
volume control to a normal level.
CW or SSB
CW or SSB
station.
CW or SSB filter
Fast Start 1
MFJ-784B Fast Start
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.
Fast Start 2
MFJ-784B Instruction Manual
Introduction
Contents of This Chapter
Introduction to DSP Page 1-2
>
Product Overview Page 1-3
>
Block Diagram Page 1-4
>
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
Introduction Error! Main Document Only.-1
MFJ-784B Instruction Manual 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 inc reased 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 u se 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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MFJ-784B Instruction Manual

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 pre­set 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 prog rammed 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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MFJ-784B Instruction Manual Block Diagram
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MFJ-784B Instruction Manual
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.
Introduction Error! Main Document Only.-5
MFJ-784B Instruction Manual 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.
Introduction Error! Main Document Only.-6
MFJ-784B Instruction Manual
Filter Specifications
Filter Left Control Right Control Attenuation7 Type8
LR/HR1 LR: 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
2BP2 f1: 300-3400 Hz f2: 300-3400 Hz 47 dB @ 60 Hz F IR
CW3 fc: 300-1000 Hz BW: 30- 700 Hz 47 dB @ 60 Hz FI R
SSB4 fc: 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 FI R
AMTOR Jumper Programmable 47 dB @ 60 Hz FIR
PACTOR Jumper Programmable 47 dB @ 60 Hz FIR
SSTV/FAX/WeFAX Fixed @1050-1350 Hz an d 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
Notch5
Random Noise
Reduction6
Note 1: The Note 2: The Note 3: The CW filter has an optional jumper-programmable sidetone filter.
Note 4: The Note 5: The multiple automatic notch has four jumper-programmable levels of aggressiveness and ables
Note 6: The random noise reduction has a variable level of noise reduction. Note 7: All FIR and II R filte r attenuati ons are cal culated in dB @ a dis tance in Hz outside the passband. All
Note 8: All FIR filters are linear phase with a 23 mS time delay and have the upper cutoff frequency limited
LR/HR
all-pass filter when LR is adjusted equal to HR. the two center frequencies.
to eliminate up to four changing tones or heterodynes.
LMS filter attenuations are dependent on the characteristics of the noise. to 3900 Hz.
filter becomes a band-stop filter when LR is adjusted higher than HR or becomes an
2BP
filter uses the bandwidth setting last used in BP filter but allows indepe nde nt vari atio n of
SSB
filter has its lower cutoff frequency limited to 175 Hz.
Entire freq. range of the received audio Up to 50 dB LMS
Entire freq. range of selected band-pass filter Up to 20 dB LMS
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MFJ-784B Instruction Manual
FIR - Finite Impulse Response IIR - Infinite Impulse Response LMS - Least Mean Square
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MFJ-784B Instruction Manual 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
: The maximum curr ent demand will be less than 500 mA at maximum
Power
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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MFJ-784B Instruction Manual
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
>
2
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MFJ-784B Instruction Manual Back Panel Connections
: This connector supplies power to the unit. It connects to a 2.1 mm
Power
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.
the MFJ-784B will perform erratically.
Warning:
V
If the power supply voltage drops below 10 volts
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.
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MFJ-784B Instruction Manual

Basic Connections

In the most simple case, the MFJ-784B will be installed in the audio path between your receiver and your headphones or speaker.
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MFJ-784B Instruction Manual Setting Receive Audio Level (Input Level)
When first connecting the DSP filter and whenever the receiver audio level changes, you should check the Input Level indicator. This LED indicates the input signal level. As a signal is received, the Input Level LED will flash from "off" to either green or red.
If the indicator flashes:
Mostly Green (never red) the input level is adjusted correctly. Any Red the input level is too high. Stays Off (or barely green) the input level is too low.
To set Receive Audio Adjust:
1. Tune your radio to the mode you will be operating most.
2. Set your
3. Use a screwdriver to adjust the Receive Audio Adjust (o n the back pa nel
of the DSP) until the Input Level LED (on the front panel) flashes mostly green and never red.
Note:
radio's
Some compromise may be required if the receiver does not maintain
volume control to a normal level.
the same audio level on different modes. Set the Receive Audio Adjust on the DSP for the most common mode, and use the receiver's volume knob to properly adjust the level when switching modes.

Increasing Headphone Audio Level

The MFJ-784B headphone level is attenuated as it co mes from the factor y. If the speaker audio is at a comfortable level and the headphone audio is too quiet, the headphone volume can be raised by using jumpers JMP 9 and JMP 10 (next to the headphones jack).
Warning: Do not short JMP 10 when using a mono phone plug or damage to your unit will result.
To raise the headphone audio level fo r mono headphones, put a 470 ohm or smaller resistor on JMP 9. For stereo headphones, put smaller resistor on JMP 10.
Installation Error! Main Document Only.-4
another
470 ohm or
MFJ-784B Instruction Manual

Passing Sidetone

You may perfer to listen to a station with different pitch than the sidetone of your transmitter. In this situation, the DSP filter will attenuate the sidetone and you will not be able to monitor your sending. There are two methods of passing sidetone through the DSP filter.

T/R Connection

preferred
The (transmit/receive) line on the DSP's To Radio port. All filter functions are bypassed when the T/R line is pulled low. The transceiver's sidetone and audio monitoring functions will appear at the DSP output without digital filtering.
The T/R line should be connected to an output from your radio that is pulled low when the radio goes into the transmit mode (such as an output for an external RF amplifier). Radio manufacturers call such a line many different names: Relay or RLY; NO or normally open; xmit, transmit or send; or maybe even PTT.
If a linear amplifier is connected to the T/R line, a diode (1N4001 or equivalent) should be connected from t he linear amplifier's contr ol (relay) jack to the T/R line. This diode prevents the amplifier from loading the DSP's T/R line when the amplifier is turned "off." The anode of the diode should be connected to the amplifier and the cathode (banded end) to the T/R line. Refer to the diagram on 2-3.
method for passing sidetone is the use of the T/R
Warning: Never connect the
T/R
line to negative voltages or to
positive voltage sources that exceed 35 volts.
The DSP has internal protection circuitry to help prevent other equipment connected to the T/R line (such as a linear amplifier) from damaging the unit.
Installation Error! Main Document Only.-5
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