MFJ MFJ-784B User manual

ME
FS Tunable DSP Filter
Model MFJ-784B
INSTRUCTION MANUAL
CAUTION: Read All Instructions Before Operating Equipment
MFJ ENTERPRISES,
300 Industrial Park Road
Starkville, MS 39759 USA
Tel: [phone] Fax: [phone]
VERSION 1B COPYRIGHT © 1995 MFJ ENTERPRISES, INC.

MFJ-784B Instruction Manual
Contents
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Basic CONNECTIONS ca2tatincets tal blnastinds ie th asnae la bamiaternnin as o-3
Setting Receive Audio Level (Input Level)... eee o-4
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MIFJ-7846 Instruction Manual
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MFJ-784B Instruction Manual
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MFJ-7B84B to PK-232 Connections wc sceseseesesen A-D
MFJ-784B to PK-BB Connections wn ccscssssssstssesceseessens A-5
Pre-set and Memory Filters Settings Chart... eee A-6

MIFJ-7 84B Instruction Manual
Before Reading This Manual
This manual is divided into two parts. The first part, called Fast Start, Is
meant far people who need to know nothing except how to minimally install
the unit and operate it on CW and SSB. The second part, chapters 1-5, 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 MFv-
7848.
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
fe = Center or Notch Frequency #2
fe = Center Frequency
BW = Bandwidth
FIR = Finite Impulse Response
IIR = Infinite Impulse Response
LMS = Least Mean Square
WPM = Words Per Minute

MFJ-784B Instruction Manual
Explanation of graphical symbol:
alert you ‘of conditions that eee be ‘damaging to th product or
resulting in a risk of electric shock to persons. ea

Amplifier
This T/R connection is used to pass sidetone.
The amplifier connection and diode are optional.
See the text on page 2-5.
1N4001 Diode
or equiv.
Transceiver |
i
Nt SPEAKER Gray - Shield
yo
AUDIO
OUT
Black
-
Conductor
RLY
(oc)
SRREEok
©)
|
TIR (Pin 5)
gemaneramemunaenscantnarn: Qasenvrerraminlecoe
ad
N-NMR ODE RCO IEA
“Ground (Pin 2)
MFJ-7846 DSP Filter
may cause undesired operation.
This device complies with part 15 of the FCC 1-TNC XMIT AUDIO 1-TNC XMITA
Rules. Operation is subject to the following two NTERPRISES, INC. 2- GROUND 2- GROUND
conditions: (1) This device may not cause harmful 3-PTT 3-
Interference, and (2) This device must accept any
| Interference’ received, Including interference that - BECEWE Uaioe EUDIO OUT
FILTERED AUDIO
OUT
HEADPHONES
SPEAKER
OQ
ADJUST
(02 ©
Center Conductor. +12 Vdc
Outside Sleeve: Ground
Warning: The MFJ-7846 will be damaged by
reverse polarity or voltages over 18 volts

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. 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
AGC button:
Program button:
Memory button:
Filters switch:
Tunable Filters left knob:
Manual Notch button:
Tunable Filters right knob:
Auto Notch button:
Noise Reduction control:
Noise Reduction button:
Volume control:
Speaker button:
DSP button:
Power button:
Position
out
N/A
out (normal)
CW or SSB
center
out
full counter-clockwise
out
full counter-clockwise
out
full counter-clockwise
Meaning
AGC off
N/A
Tunable/ Pre-set
CW or SSB filter
middle center freq.
manual notch off
widest bandwidth
auto notch off
minimum reduction
noise reduction off
minimum volume
speaker on
DSP bypassed
MFJ-7 848 off
3. Apply external power and press and lock the DSP's Power button. The
PWR LED on the front panel should light red.
Memory 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.
If it is green, press the
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).
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.
Press and hold the red Program button. You will hear a tone.
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.
Slowly adjust the right Tunable Filters control (bandwidth or BW)
clockwise. The CW station's signal should become clearer (less noise
and QRM).
Practice on other single stations and even with several CW stations
sending at the same time. With practice, you will be able to separate
mixed signals and copy signals that were undetectable without the
filter. Also, 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.
Adjust the right Tunable Filters contro! [bandwidth or BW) clockwise
to make the SSB signal clearer (less noise and QRM) while not
making the signal less intelligible.
Adjust the left Tunable Filters control (center frequency or fc) to
peak the signal for maximum intelligibility.
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.
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.
Préss 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.
Experiment with different filter adjustments and functions under
various conditions to become familiar with the various controls.
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 MFU-784B.
Fast Start 2

MFJ-784B Instruction Manual
1
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 1-1

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 (QRIV).
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 rea/ 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-2 105, 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.
Introduction 1-2

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 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
<BP 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/FAK/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, RITY, HF PACKET, AMTOR, PACTOR, and
SSTV/FAX/ WeFAX.
The naise 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.
Introduction 1-3

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Internal
Jumpers
Anal Receive
ie og Audio
Filter Adjust
T/R
Front Fanel
Controls
Custom
Memory
oS Headphones Jack
Digital Signal Processor
(DSP)
Analog to Digital
CODEC
Digital to Analog
Filtered
Ta Audio
Pre- Line > pale
Am : Volume Amo
ae E Control ae
Speaker Jack
es
° Power
Speaker Switch Switch (a)
Receive
Audio
In
TNC
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Audio
Out of
Filter
Filtered
Audio
Out
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AGC Fitters
Front Panel Layout
MODEL
Filters
MFJ-784B
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VIF J-7 84B Instruction Manual
Noise
h
pmmneert es (eo SSB—— sB—— BW Reduction volume
e 6)
OFF out ore SL
Manual Notch Auto Notch
Noise Reduction Speaker OSP Power /
AGC button:
Program button:
Memory button:
Filters switch:
PWR LED:
Input Level LED:
Tunable Filters left knob:
Manual Notch button:
Tunable Filters right knob:
Auto Notch button:
Noise Reduction knob:
Noise Reduction button:
Volume control:
Speaker button:
DSP button:
Power button:
Press to enable the automatic gain control;
press again to turn it off.
Press to program memory filters, to talk, or to
activate CW spotting tone.
Selects either normal or memory filters mode.
Selects one of ten normal or ten memory
filters.
Indicates normal (red) or memory (green) mode.
Indicates input signal level (red too high, off too
low, green is OK).
Adjusts tunable filters and manual notch.
Press to enable the manual notch, press again
to turn it off.
Adjusts tunable filters and manual notch.
Press to enable the autamatic notch; press
again to turn it off.
Controls the level of noise attenuation.
Press to enable the noise reduction; press
again to turn it off.
Controls the output volume level to speaker
and headphones jacks.
Press to enable the speaker jack; press again
to turn it off.
Press to turn on digital processing of input
signal; press again to bypass processing.
Press to turn the power on; press again to
turn the power off.
For an in-depth description of the front panel controls, refer to chapter 3,
Operation.
Introduction 1-5

MIF J-784B Instruction Manual
Back Panel Layout
This device complies with pert 15 of the FCC
Rulea. Operetion le eubject to the following two
oonditiona: (1) Thie device may not oauee harmful
Interference, and (2) Thie device muet accept eny
interference received, Including interference that
mey cause undesired operation.
- TNC XMIT AUDIO
MFJ ENTERPRISES, INC. 37 tox" :
STARKVILLE, MS USA 7777 ae
§ &
+ TNC XMIT AUDIO
RECEIVE AUDIO IN 4- FILTERED AUDIO OUT
-TIA > NO CONNECTION
TO T
FILTERED AUDIO | RECEIVE AUDIO RADIO
INC
ADJUST oUT | ADJUST IN
BOie
MIN
MAX
©)
MIN
MAX
(©)
640
ra)
Nd
35241
»
HEADPHONES
POWER
SPEAKER
' OUT
ges
©) © 6
Sat
12Vde
500mA
Power:
Headphones Out:
Speaker Out:
Filtered Audio Adjust:
Filtered Audio Out:
Receive Audio Adjust:
Receive Audio In:
To Radio:
To TNC:
10-16 Vdc @ .5 amp peak [low "Z " audio load)
1/4" stereo ar mono phone jack
3.5 mm stereo or mono phone jack
screwdriver adjustable potentiometer
RCA phono jack (~1.5 V P-P @ 600 ohms}
screwdriver adjustable potentiometer
RCA phono jack
5-pin DIN jack
(TNC xmit audio, ground, PTT, receive audio in, T/R)
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 1-6

MFJ-784B Instruction Manual
Filter Specifications
Left Control Type
LR/HR"
fc: 600-1700 Hz BW:1000-2500 Hz
Jumper Programmable
Jumper Programmable
Jumper Programmable
Jumper Programmable
Fixed @1050-1350 Hz and 1450-2350 Hz
Manual Notch f2: 150-3400 Hz
Manual Notch (CW mode] fe: 300-1000 Hz
Notes
1 The LR/HR filter becomes a band-stop filtér when LR is adjusted higher than HR.
2 The 2BP filter uses the bandwidth setting last used in BP filter but allows independent
variation of the two center frequencies.
3 The CW filter has an optional jumper-programmable sidetone filter.
4 The SSB filter has its lower cutoff frequency limited to 175 Hz.
S The multiple automatic notch has four levels of aggressiveness.
-6 The random noise reduction has a variable level of noise reduction.
_7 All FIR and IIR filter attenuation is indicated in dB @ a distance in Hz outside the passband.
All LMS filter attenuation is dependent on the characteristics of the noise.
2Bpe
ssp
Q
w
HF PACKET
AMTOR
PACTOR
SSTV/FAX/WeFAX
FIR
FIR
FIR
FIR
FIR
FIR
FIR.
FIR
FIR
FIR
Ms
MS
e All FIR filters are linear phase with a 23 mS time delay and have the upper cutoff frequency
limited to 3900 Hz.
FIR - Finite Impulse Response __ IIR - Infinite Impulse Response LMS - Least Mean Square
Introduction 1-7

MFJ-784B Instruction Manual
Unit Specifications
General Specifications
Processor: Analog Devices ADSP-2105. Data width - 16 bits. Clock speed -
12 Mz.
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 {160 mW @ 6 achms]. 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).
Introduction 1-8

MFJ-784B Instruction Manual
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
Installation 2-1

MFJ-784B Instruction Manual
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. /f the power supply voltage drops below 70 |
volts the MFJ-784B will perform erratically.
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 or
walkman type headphones with 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 |n: 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.
Installation 2-2

MFJ-784B8 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.
Am plifier
This T/R connection is used to pass sidetone.
The amplifier connection and diode are optional.
See the text on page 2-5.
1N4001 Diode
or equiv.
Transceiver
ore SPEAKER Gray - Shield
a, AUDIO OUT Black - Conductor RLY
Ete % Use a quality RCA cable
( oo ) for the audio connection. ( Oo}
3h
ge
a
9
see
MFJ-7846 DSP Filter
This device ocompllee with part 15 of the FCC
Rules. Operation Is eubjeot to the follewing two
conditions: (1) This device may not cause harmful
interference, and (2) This device must accept any
interference received, Including Interference that
may cause undesired operation.
Ground (Pin 2
< TNC XMITAUDIO. —-1- TNC XMITA\
NTERPRISES, INC. 2: crouno 2- GROUND
-PTT 3-
- RECEIVE AUDIO IN 4
-T/A
HEADPHONES
ADJUST out
OUT SPEAKER
OUT
2 ©}
Center Conductor: +12 Vdc
Outside Sleeve: Ground
Narning: The MFJ-784B will be damaged by
reverse polarity or voltages over 18 volts
Installation 2-3