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MFJ-8100
World Band Receiver

21

Throughout this instruction manual, we use plain English as
much as possible. But there's no way around using common
electronics terms and abbreviations where appropriate. We
simply try to avoid "jargon'' that is unnecessary. The
following mini-glossary was compiled as a help to beginners
work with this unit. Our descriptions are NOT intended to be
complete definitions.

For a very clear and economical explanation of electronics
parts and how they work, see Getting Started in Electronics
by Forrest Mims III, No. 276-5003, at any Radio Shack store.

Alignment -

One-time adjustment of internal controls in a

radio circuit. (See also: Trimmer)

AM -

Amplitude Modulation

Band - a related group of frequencies

Board - short for "printed circuit board'' or circuit board.

Bridge, Solder - the unintentional joining of two or
more points on the solder-side of a printed circuit
board.

Carrier

-

the steady tone or whistle that is the

foundation of an AM or FM voice signal. In most
receivers, the carrier is not even heard, because
regeneration or a BFO or direct-conversion is
required to convert the carrier energy into an
audible tone.

CW -

Continuous Wave - refers to Morse Code signals

DC -

direct current (example: battery voltage in contrast
to household AC from the wall outlet.) DC sometimes
refers to "direct conversion'' receivers: see below.

Detector -

the section of any radio that changes radio

energy into audio energy intended for listening.

Direct Conversion - a popular type of simple receiver for CW-

SSB which needs no regeneration control but which
does not permit pleasant listening to AM shortwave
broadcasts, because the carrier (see above) as well
as the voice modulation can be heard.

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Содержание MFJ-8100

Страница 1: ...the Regeneration Control Page 7 Tuning SSB Voice Signals Page 8 Using and Enjoying Your Receiver Page 9 Setting Up A Useful Shortwave Antenna Page 9 Your Receiver Audio Circuit Page 10 About the 5 Tuning Ranges of Your Receiver Page 11 Shortwave Listening in General Page 12 In Case of Difficulty Page 12 Notes for Radio Hams Experimenters Page 13 Conclusion Page 14 Some Helpful Terms Abbreviations ...

Страница 2: ...MFJ 8100 World Band Receiver 2 Instruction Manual written by Dan F Onley K4ZRA Copyright 1993 by MFJ Enterprises Inc All Rights Reserved ...

Страница 3: ...king glowing boxes were the norm for home listening as well as for the first generation of radio hams Receiver design evolved swiftly The superheterodyne became the norm during the 1930 s Regenerative receivers often called Gennies were left to tinkerers and beginners Even though these receivers were simple and quite sensitive they had a number of shortcomings instability touchiness difficulty in ...

Страница 4: ...nd the Future Your MFJ 8100 is a much better receiver than the classic radio sets which attracted several generations of Americans to the excitement of radio and electronics In fact its basic performance is superior to many of the simplest superhet receivers which were considered such a great step beyond one s first regenerative set The reason why this receiver works so well is because there is mu...

Страница 5: ...ing amplifier The regeneration circuit repeatedly feeds the detected signal back to the input which boosts its strength many hundreds of times This feedback process must be carefully controlled which is the function of the regeneration control The frequency of oscillation is determined by the choice of inductors bandswitch and the setting of the tuning capacitor If the oscillator is tuned to 10 1 ...

Страница 6: ...ue listenability Similarly a multi band superhet with BFO could not fit our goals of simplicity and economy To meet our goals we chose to refine the regenerative concept as much as possible using contemporary design concepts and component characteristics Our first goal was to tame the regeneration process itself to minimize the instability and unwanted oscillations so typical of traditional regene...

Страница 7: ...s which permitted the oscillating detector to behave as an unstable but potent QRP transmitter R4 reduces the Q of L1 10 uH for smoother regeneration The SW1 bandswitch selects a combination of simple inductors For example the total inductance for Band A is L1 L2 L3 L4 L5 The inductance for Band E is only L5 And so forth Air variable C1 uses its 50 pF range and mechanical vernier reduction to prov...

Страница 8: ...MFJ 8100 World Band Receiver 8 To prolong useful battery life R13 limits current draw by the LED CR1 to minimum reasonable visibility as an on off indicator ...

Страница 9: ...in use A weakened battery degrades receiver performance REGENERATION R1 Because understanding and controlling regeneration is at the heart of your receiver s performance we ve provided a separate section on its use In brief it controls receiver sensitivity and adjusts between AM broadcasts and CW SSB VOLUME R2 This potentiometer performs the normal function of any volume control Of interest to the...

Страница 10: ...any wire or a banana plug may be inserted in its end 10 to 20 feet of ordinary hookup wire also called bell wire provides good basic reception even when installed indoors See the section on Antennas in this book for more information GROUND CONNECTION For casual operation a ground connection is optional However a wire from this connector to a ground rod or cold water pipe will reduce unwanted noise...

Страница 11: ...ong shortwave AM broadcasts in a given band such as is common in the early evening you will find it possible to tune them in one after the other with the regeneration control set way back and requiring virtually no adjustment In other words you would tune from station to station just as if using any other type of shortwave set When the receiver is adjusted for good AM reception CW signals will sou...

Страница 12: ...OWER sideband tune DOWN for UPPER sideband tune UP In practice this means that you would approach the LSB signal by tuning from higher frequency right to lower left from higher voice pitch to lower pitch Here s how to do it step by step 1 Pick out a strong high pitched Donald Duck voice 2 Turn the tuning knob ever so slightly to the left 3 If the pitch of the voice went DOWN slightly you re headin...

Страница 13: ... the time Bands D and E assure a variety of daytime reception but also can be busy at night 4 The audio circuit is designed for one or two pairs of Walkman stereo headphones or mini speakers Other speaker options are mentioned in Section XX IMPORTANT The internal 9 volt battery will provide many hours of satisfying listening provided that you turn the receiver OFF when not in use This advice may s...

Страница 14: ...led random long wires and also work fine in most attics Foil backed insulation or metal roofing will reduce the usefulness of an attic as antenna space Your antenna can be horizontal vertical or a combination of both It can be tubing or pipe as well as wire The wire can be bare or insulated It could be something not intended to be an antenna such as a gutter fence flagpole or metal roof In fact ra...

Страница 15: ...lifier can also be a rewarding do it yourself construction project One half to 2 watts will provide generous and ample speaker volume In fact if building this receiver has kindled your interest in building something on your own you could get started by duplicating the same LM386 audio circuit used in this receiver Use the same parts values and physical positioning as we did The volume control may ...

Страница 16: ...is printed in this book which you may copy to make your own logbook Or use your computer to design the style of logging pages best for you Range A 3 5 to 4 3 MHz The primary purpose of this tuning range is to make it very easy for you to listen to ham radio stations at night on what is known as the 80 75 Meter band From 3 5 to 3 8 MHz you ll hear mostly Morse Code signals From 3 8 to 4 0 MHz you w...

Страница 17: ...iety during daylight hours It includes the 16 Meter broadcasting band 17 55 to 17 9 MHz the 17 Meter ham band 18 068 to 18 168 MHz and the 15 Meter ham band 21 0 to 21 45 MHz Station WWV also broadcasts on 20 MHz SHORTWAVE LISTENING IN GENERAL In addition to the specific bands highlighted above you ll hear thousands of OTHER shortwave signals Many will be military or government Morse code transmis...

Страница 18: ...in the skill of finessing the regeneration control to choose AM shortwave broadcasts SSB or CW RTTY The MFJ 8100 just might be the very best regenerative receiver ever designed but it is not intended to be all things to all people The MFJ 8100 s PC board is a very roomy platform which may SEEM to invite countless modifications However please remember the original purpose of the receiver before hac...

Страница 19: ... keying sidetone Frequency spotting must be done with a very low RF level Receiver stability when switching the antenna input is amazingly good even at 21 MHz While the 8100 is not represented as a communications receiver you indeed can have some multi band QRP fun with it And FUN is exactly what this great new receiver is all about Look at it this way If you take your multi band QRP mini transmit...

Страница 20: ... who are young at heart Getting Started in Electronics by Forest Mims III Radio Shack Now You re Talking Discovering the World of Ham Radio ARRL Newington CT 06111 also sold by Radio Shack Plus these MFJ publications Shortwave Listener s Guide for Apartment Condo Dwellers by Ed Noll W3FQJ 1991 MFJ Edition No 36 The Wonderful World of Ham Radio by Richard Skolnik KB4LCS 1990 MFJ Edition No 35 Or if...

Страница 21: ...nted circuit board or circuit board Bridge Solder the unintentional joining of two or more points on the solder side of a printed circuit board Carrier the steady tone or whistle that is the foundation of an AM or FM voice signal In most receivers the carrier is not even heard because regeneration or a BFO or direct conversion is required to convert the carrier energy into an audible tone CW Conti...

Страница 22: ...stic rectangular block with 6 8 14 or more pins containing a silicon chip which provides the equivalent of dozens or hundreds of individual transistors and resistors K abbreviation for 1000 ohms 10K 10 000 ohms KHz KiloHertz MHz MegaHertz Inductor A coil or loop of wire used in electronic circuits Oscillator see Regeneration pF picofarad a tiny unit of capacitance megohm one million ohms Regenerat...

Страница 23: ...arked on the part Toroid a type of coil consisting of wire wrapped around a donut shaped form such as L5 in this receiver Trimmer a miniaturized variable resistor or capacitor used for occasional circuit adjustments uF micro farad the usual unit of capacitance uH micro henry a unit of inductance Sample SWL Logging Page Date UTC GMT Name and Location of Broadcast service Call sign Band or Frequenc ...

Страница 24: ...MFJ 8100 World Band Receiver 24 ...

Страница 25: ...0 uF electrolytic 203 0015 C14 10 uF electrolytic 203 0012 C16 75 pF 200 1011 C18 1 uF electrolytic 203 0006 C19 470 uF electrolytic 203 0004 CR1 LED 320 0001 IC1 LM386 audio amp 311 0386 L1 10 uH 401 0102 L2 3 3 uH 401 0045 L3 1 uH 401 0037 L4 47 uH 401 0015 L5 T 52 2 toroid 8T 403 1003 Q1 Q3 J310 FET 305 6310 R1 10K pot 162 4100 1 R2 250 ohm pot volume 162 2250 1 R3 R5 R8 10K 100 4100 R6 R9 1K 1...

Страница 26: ...and Receiver 26 R20 100K trimmer 130 5100 J1 Antenna connector 06 0003 J2 J2 Stereo 1 8 jack 601 4010 SW1 5 position switch 500 0024 SW2 push switch 504 0022 Note C 20 C 22 27 R10 R14 16 R 18 are not used PC Board View ...

Страница 27: ...MFJ 8100 World Band Receiver 27 Schematic Diagram ...

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