MFJ MFJ-784B User Manual

MFJ-784B Instruction Manual

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

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

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
ii

MFJ-784B Instruction Manual

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

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 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

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	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).

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 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.

Introduction Error! Main Document Only.-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 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 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.

Introduction Error! Main Document Only.-3

MFJ-784B Instruction Manual

Block Diagram

Introduction Error! Main Document Only.-4

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
Memory button:	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
Tunable Filters left knob:	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
Speaker button:	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
To TNC:	(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	FIR
CW3	fc:	300-1000 Hz	BW:	30700 Hz	47 dB @ 60 Hz	FIR
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	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	Entire freq. range of the received audio				Up to 50 dB	LMS
Notch5
Random Noise	Entire freq. range of selected band-pass filter				Up to 20 dB	LMS
Reduction6

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 limited to 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 random noise 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.

Introduction Error! Main Document Only.-7

MFJ-784B Instruction Manual

FIR - Finite Impulse Response

IIR - Infinite Impulse Response

LMS - Least Mean Square

Introduction Error! Main Document Only.-8

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

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).

Introduction Error! Main Document Only.-9

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

Installation Error! Main Document Only.-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. If the power supply voltage drops below 10 volts the MFJ-784B will perform erratically.

Warning: Voltages 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.

Installation Error! Main Document Only.-2

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.

Installation Error! Main Document Only.-3

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)

Any Red

Stays Off (or barely green)

To set Receive Audio Adjust:

the input level is adjusted correctly. the input level is too high.

the input level is too low.

1.Tune your radio to the mode you will be operating most.

2.Set your radio's volume control to a normal level.

3.Use a screwdriver to adjust the Receive Audio Adjust (on the back panel of the DSP) until the Input Level LED (on the front panel) flashes mostly green and never red.

Note: Some compromise may be required if the receiver does not maintain 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 comes from the factory. 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 for mono headphones, put a 470 ohm or smaller resistor on JMP 9. For stereo headphones, put another 470 ohm or smaller resistor on JMP 10.

Installation Error! Main Document Only.-4

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

The preferred method for passing sidetone is the use of the T/R (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 the linear amplifier's control (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.

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

+ 51 hidden pages