QRPKits DC40A User manual

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The DCxxA Family of Transceivers
High Performance Direct Conversion Transceivers for 40, 30 and 20 eters
DC30A Transceiver
Evolution of the popular DC40 to the DCxxA series on 40, 30 and 20 eters
A KD1JV “ elt Solder” Design
Distributed by Hendricks QRP Kits
www.qrpkits.com
Join Yahoo’s DC40 Kits group for support from other buil ers an information about operation an mo ifications.
Be sure to inclu e your call an real name with your request
. http://groups.yahoo.com/group/ c40kits/

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The DCxxA
A Direct Conversion, Fixed-Frequency Transceiver for 40, 30 and 20 eters
The DCxx is a mo erately complex rig, which yiel s excellent performance, yet is small enough to fit into
an Altoi s tin. The receiver features nearly complete immunity to AM SWBC interference an can be run on an AC
supply with little hum pickup or AM BC interference common to most DC receiver esigns. One stage of au io
ban pass filtering gives the receiver some selectivity. The transmitter puts out a respectable 750 mW of power,
with a 12V supply an over 1 Watt with 13.8 volts. The transmitter frequency is automatically shifte up about 600
Hz to provi e the proper T/R offset. The rig also inclu es a simple keyer chip.
Assembly:
Review the entire manual and inventory the parts for each group before proceeding.
Assembly of the boar will be one in several groups. You may fin it convenient to separate the parts for
each of the groups as shown in the parts lists for each group.
You can “smoke test” most of these groups when finishe , or move on to the next group an test
everything at once. If a group fails to pass the smoke test, see the trouble shooting section locate after the
assembly instructions.
If you plan on installing the boar into an Altoi s tin, trim off the corner of the boar next to the pa le jack
before you install the jack. You may also want to mark where the mounting holes an where the phone jacks will
be in the tin before installing any parts.
The parts location iagram for the whole boar is shown below. Component values are marke in re .
Experience buil ers shoul be able to buil up most of the boar using just this iagram.
Steve an Doug wish to thank Chuck Carpenter, W5USJ, for manual e iting an revisions. Also our thanks to Jay Bromley,
W5JAY, Tony Fishpool, G4WIF an Davi Yarnes, W7AQK, for kit testing an manual proof rea ing.

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Parts list
RESISTOR VALUE TYPE Caps Value Type
R1 1 meg 5% 1/4w CF C1 .012 uF FILM
R2 360 K 1.00% C2 330 p Mono or Disk
R3 1 meg C3 .1 uF Mono
R4 1 K C4 .1 uF Mono
R5 1 K C5 .012 uF FILM
R6 10 OHMS C6 Skippe Not use
R7 1 K C7 Ban specific See page 5 Mono or Disk C0G
R8 1 MEG C8 40 p YEL TRIMMER
R9 100 K C9 22 uF / 16V ALUM
R10 1.5 K C10 .001 uF Mono or isk
R11 36 K 1.00% C11 .1 uF Mono
R12 22 K C12 .1 uF Mono
R13 Skippe Not use C13 100 uF/16V ALUM
R14 Skippe Not use C14 Skippe Not use
R15 100 OHMS C15 330 p Mono or Disk
R16 100 K C16 Skippe Not use
R17 15 K C17 .001 uF Mono or Disk
R18 10 ohms C18 .001 uF Mono or Disk
R19 15 K C19 .001 uF Mono or Disk
R20 Skippe Not use C20 .1 uF Mono
R21 Skippe Not use C21 100 p Mono or Disk C0G
R22 470 ohms C22 100 uF/16V ALUM
R23 10 K C23 Ban specific See page 5 Mono
R24 100 OHMS C24 .1 uF Mono
R25 51 OHMS C25 .1 uF Mono
R26 10 ohms C26 .1 uF Mono
R27 470 ohms C27 . 1 uF Mono
R28 100 K C28 Ban specific See page 5 Mono or Disk C0G
R29 Skippe Not use C29 Ban specific See page 5 Mono or Disk C0G

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R30 10K C30 Ban specific See page 5 Mono or Disk C0G
T1 Ban Specific See page 5 C31 Ban specific See page 5 Mono or Disk C0G
T2 See page 13 C32 100 p Mono or Disk C0G
T3 See page 11 C33 Ban specific See page 5 Mono or Disk
L2/3 Ban Specific See page 5 C34 40p YEL TRIMMER
C35 4.7uF/16V ALUM
C36 .001 u Mono or Disk
C37 .1 u Mono
C38 .001 u Mono or Disk
C39 .001 u Mono or Disk
C40 .01 u Mono
C41 Ban specific See page 5 Mono or Disk C0G
Semiconductors
X1 crystal U1 NJM4556AD High current opamp
SWITCH 6mm TACT 14mm shaft U2 74HC4053 Analog multiplex
U3 ATTINY11 MPU
U4 LM78L05 5V Regulator
JACKS PC mount stereo Hea phone,
Pa le
PC Boar Q1 PN2222A NPN
Re an Green Magnet wire Q3 2N3904 NPN
2, 8-pin IC sockets Q2/4/5/6/7/8/9 2N7000 Tfet
16-pin IC socket Q10 2N3819 j-fet
D1/2/10 1N4148
D9 1N5817

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Band specific values
Location 40M 30M 20M Type
C31 47p 47p 22p C0G Mono or Disk
C33 100p 47p 22p C0G Mono or Disk
C7 47p 33p Not use C0G Mono or Disk
C28 330p 220p 150p C0G Mono
C29 680p 560p 330p C0G Mono
C30 330p 220p 150p C0G Mono
C23 68p 68p 33p C0G Mono
C41 Not use 68p 100p C0G Mono or Disk
Toroid Winding Charts
40 eters Wire Core Turns Wire Length
L1 (Not Used)
L2 #28 Re T37-2 (re ) 21T 16”
L3 #28 Re T37-2 (re ) 16T 12”
T1 #28 Re /Green T37-2 (re ) 35T Pri/5T Sec. 24” Re , 6” Grn.
T2 #28 Re /Green FT37-43 6T Bifilar 10” Re , 10” Grn
T3 #28 Re /Green BN2402-43 5T Pri/1T Sec 5” Re , 2” Grn
30 eters Wire Core Turns Wire Length
L1 (Not Used)
L2 #28 Re T37-2 (re ) 15 11”
L3 #28 Re T37-2 (re ) 13 10”
T1 #28 Re /Green T37-2 (re ) 35T Pri/5T Sec. 24” Re , 6” Grn.
T2 #28 Re /Green FT37-43 6T Bifilar 10” Re , 10” Grn
T3 #28 Re /Green BN2402-43 5T Pri/1T Sec 5” Re , 2” Grn
20 eters Wire Core Turns Wire Length
L1 (Not Used)
L2 #28 Re T37-6 (yellow) 17 13”
L3 #28 Re T37-6 (yellow) 13 11”
T1 #28 Re /Green T37-2 (re ) 25T Pri/5T Sec. 29” Re , 6” Grn.
T2 #28 Re /Green FT37-43 6T Bifilar 10” Re , 10” Grn
T3 #28 Re /Green BN2402-43 5T Pri/1T Sec 5” Re , 2” Grn

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.
Examples of Component Types
Note variations in shape, size an color of similar component types. Some component lea s will nee to be
reshape to fit the holes in the PCB.

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Tips and Info for First Time Builders
Installing parts:
You can insert several parts at a time onto the boar . Parts shoul be presse flush to the top of the boar . The
exception are the transistors which shoul stan off the boar by about 1/8” ue to their three legge nature. Once
you insert the part, kink one of the lea s over slightly to keep it from falling out of the boar when you flip the boar
over to sol er.
The .1 uF caps use in the kit have forme lea s, so these will not sit quite flush to the boar . Several of the isc
caps have lea spacing larger than the pa s on the boar . You can reform these lea s with your pliers so they will
sit flush to the boar .
Once you sol er a part in place, clip the lea nearly flush to the boar . Clip at the top of the little fillet of sol er
which forms aroun the lea .
Fin ing the right part.
A picture at the bottom of the parts list on the previous page can be use to help i entify some of the parts. The
parts not shown shoul be obvious or e uce by the process of elimination. The numbers i entifying the
monolithic caps (mostly yellow or blue in color) can be har to rea . The use of a magnifying glass can help you to
see them. In a ition to the part value of the capacitor, there are a number of other letters an numbers printe on
the part. Simply look for the three number group which matches the value your looking for, 331 for 330 pF, 104 for
.1 uF, 681for the 680 pF cap an so on.
IC pin 1.
The outline on the boar for the ICs has a “V” notch on one en . This in icates the pin 1 en of the IC. If a socket
is use , there is also a notch on one en of the socket. This en goes over the V notch outline on the boar .
Finally, pin 1 of the IC is marke with a roun imple or ot. This en of the IC will go towar s the notch on the
socket or “V” on the outline.
Sol ering
There are two important things which nee to be one to ensure the successful operation of a kit. One is getting
the right part into the proper place on the boar . The secon is goo sol ering. To ensure a goo connection, the
sol ering iron shoul touch both the component lea an the circuit boar pa it’s to be sol ere too. Heat the
connection for just a secon , then put the sol er to the iron/pa /lea junction. Allow just enough sol er to flow to fill
the hole an wick aroun the lea . Go easy on the sol er, you on't nee a whole lot. If you use a thin sol er like
0.02” instea of the more common 0.032” type, you have better control of the amount of sol er use . For parts
which connect to the groun plane, you may have to heat the connection a little longer.
Coils an Transformers
You may fin it convenient to win an prepare all of the coils an transformers before you start inserting parts.
That way you on’t nee to stop an possibly loose concentration to win an them for installation. See page 5 for
ban specific etails.

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Group 1: Power, Audio and Keyer stages.
NOTES:
Do not install the ICs into the sockets until after the initial smoke test. R11 an R2 are 1% resistors, so have four color ban s
for the value, instea of three for the 5% resistors. They also may have a blue bo y color, instea of tan. On C9, C13 an C22
the long lea is + an the negative lea si e is marke with a black strip on the cap bo y. Dio es D1 an D2 are installe “back
to back”, therefore, the black ban on the io e (catho e en ) shoul be facing in opposite irections from each other.
Part # value markings PART# VALUE MARKINGS TYPE
R1 1 MEG BRN/BLK/GRN R30 10K BRN/BLK/ORN
R3 1 MEG BRN/BLK/GRN C4 .1 uF 104 Mono
R4 1 K BRN/BLK/RED C11 .1 uF 104 Mono
R5 1 K BRN/BLK/RED C12 .1 uF 104 Mono
R7 1 K BRN/BLK/RED C20 .1 uF 104 Mono
R10 1.5 K BRN/GRN/RED C25 .1 uF 104 Mono
R9 100 K BRN/BLK/YEL C10 .001 uF 102 Mono or Disk
R6 10 Ohm BRN/BLK/BLK C17 .001 uF 102 Mono or Disk
R11 36K, 1% ORG/BLU/BLK/RED C18 .001 uF 102 Mono or Disk
R2 360K, 1% ORG/BLU/BLK/ORG C19 .001 uF 102 Mono or Disk
R8 1MEG BRN/BLK/GRN C1 .012 uF 123 FILM (Brown)
R15 100 ohms BRN/BLK/BRN C5 .012 uF 123 FILM (Brown)
D9 1N5817 Schottky C2 330 p 331 Mono or Disk
D1/D2 1N4148 io e C15 330 p 331 Mono or Disk
U4 78L05. +5 regulator C21 100 p 101 Mono or Disk
U1/3 socket 8 pin C9 22u/16V 22/16 Alum RADIAL ALUM ELECTRO
pa le jack stereo C13 100u/16V 100/16 Alum RADIAL ALUM ELECTRO
phone jack stereo C22 100 u/16V 100/16 RADIAL ALUM ELECTRO

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Connection of jumper from U4-3(output) to U1-3 required for missing 5V buss PCB trace.
There was a mistake ma e when the boar was lai out an the connection shown below was misse . The kit
buil er nee s to sol er a jumper in place as shown. A soli insulate wire, 26 or 28 ga, shoul be use for the
connection. Sol er the jumper in place after U1 an U4 are sol ere .
Smoke Test:
Connect the positive lea of a 12V power source to the hole marke “+V”. Connect the negative lea to the hole marke “GND”.
You can tack these to the bottom of the boar , so they are easy to remove uring further assembly. Apply power to the boar .
Using a voltmeter, verify there is about 5 volts between pins 4 (groun ) an pin 8 (+V) on U3. If this tests goo , remove power
an insert U3, the ATTINY11 keyer chip an U1, the 4556 op amp. Insert a pair of hea phones into the phones jack an a
pa le or straight key into the pa le jack. Restore power to the boar . Using the pa le or straight key, you shoul hear the
si e tone in the hea phones. (You may fin it easier to use the final power lea s rather than tack in test lea s.)

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Group 2: Receiver front end:
NOTES:
C8: the flat si e of the trimmer goes towar s the line on the
outline.
U2: Install the 16-pin socket at the U2 position. Be sure the
notch is positione to match the notch shown on the boar .
Then install U2 into the socket orienting the ot an notch.
T1: Ban Specific Transformer, See Page 5
Using the re wire an a re T37-2 core, win the require number of turns for the ban you
are buil ing. Keep the turns snug an as close together as you can. This is the secon ary
win ing (SEC). Win 5 turns of the green magnet wire in the space between the start an
finish of the secon ary win ing. This is the primary or link win ing (LINK) You can overlap
these turns if there isn't enough room to make a single layer. Trim back the lea s to about
1/4” an tin. Tinning can be one with a HOT sol ering iron. It helps to have a blob of sol er
on the tip when you o this. Start at the wire en an move back towar the core. Insert the
two re wire lea s into the holes labele “SEC” on the iagram an the two green wires into the holes labele
“LINK”. The two holes on the left (closest to the e ge of the boar ), are both groun , so it oesn't matter if the SEC
an LINK wires on this en are crosse . Trim the T1 lea s after they are sol ere .
location value markings
R26 10 ohms BRN/BLK/BLK
R12 22 K RED/RED/ORG
R28 100 K BRN/BLK/YEL
R27 470 ohms YEL/VIO/BRN
C3 .1 uF 104 Mono
C37 .1 uF 104 Mono
C26 .1 uF 104 Mono
C38 .001 uF 102 Mono or Disk
C39 .001 uF 102 Mono or Disk
C36 .001 uF 102 Mono or Disk
C7 Ban
specific
See page 5
C8 40p Yellow trimmer
Q10 2N3819 jfet
Q8 2N7000
U2 Socket 16-pin
Q7 2N7000
Q9 2N7000
U2 74HC4053
T3 See text
T1 Ban
Specific
See page 5

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T3: This coil is woun on a small binocular core. One turn is a pass through both holes. The
secon ary is a single turn, one hairpin passe through both holes. Insert this wire first. You
might want to mark the secon ary en with a ot of nail polish. Then win the primary, 5 turns,
starting from the other si e of the core from which the secon ary exits. Try to keep the wire
snug to the insi e of the core, or it might be har to get all the turns in.
Smoke test: There is no test for this group, move on to the next group.

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Group 3: Oscillator:
NOTE:
The 2N7000s are mosfets an can be amage by static.
Those who live in ry areas an prone to static problems nee
to take precautions before han ling. This can simply be to
touch a large metal object to ischarge your self, before
han ling the parts.
C34: The flat si e of the trimmer goes towar s the line on
layout iagram. C41 not use in 40M version.
S1: You may want to mount the switch on the bottom of the
boar . If you are going to mount the rig into an Altoi s tin, you
won't have to open the li to access the switch. If you mount
the rig into some other kin of enclosure, using a separate
push button or mounting the switch on the bottom may be the
only practical way of accessing it.
Crystal Socket: If you want to change frequencies, you may
want to install a SIPP socket at location X1. An example of
preparation an installation of the SIPP socket can be foun at
http://www.qrpkits.com/buil ertip03.html.
Smoke Test:
Connect a pa le an hea phones to the boar . Connect a
test lea antenna to your “big rig” an select the ban for
which this kit is being built. Tune the receiver to the crystal
frequency. Place the test lea antenna near the boar . Apply
power. Tune the receiver aroun a little until you hear the
boar ’s crystal oscillator. Click an hol close the switch until
you hear the letter “T” in the hea phones. The keyer is now in
Tune mo e. Tapping the DASH pa le will put the rig into
transmit mo e. It will remain so until you tap the DOT pa le.
You can continue to toggle back an forth between transmit
an receive using the DOT an DASH pa les. To exit tune
mo e, click the switch again.
Now you can set the C34 trimmer for the proper T/R
oscillator shift. With the boar in receive mo e, note the
frequency of the oscillator. Toggle the boar into transmit
mo e an a just the C34 trimmer so the oscillator is now 600
Hz higher in frequency than it was when in receive mo e. You
can also make this a justment with a frequency counter if you
have one. The right han si e of R12, locate just below U3, is
a convenient place to connect a counter.
location value markings
R18 10 ohms BRN/BLK/BLK
R25 51 ohms GRN/BRN/BLK
R24 100 ohms BRN/BLK/BRN
R22 470 ohms YEL/VIO/BRN
R20 10 K BRN/BLK/ORG
R23 10 K BRN/BLK/ORG
R17 15 K BRN/GRN/ORG
R19 15 K BRN/GRN/ORG
R21 22 K RED/RED/ORG
R16 100 K BRN/BLK/YEL
C31 See page 5 Ban Specific
C33 See page 5 Ban Specific
C32 100 p 101 DISK
C41 See page 5 Ban Specific
C27 .1 uF 104 Mono
C40 .01 uF 103 Mono
C34 40p Yellow trimmer
C35 4.7 uF/16V Alum Electro
Q1 PN2222A NPN
Q3 2N3904 NPN
Q2 2N7000 mosfet
Q4 2N7000 Mosfet
Q5 2N7000 mosfet
Q6 2N7000 mosfet
D10 1N4148 io e
X1 Crystal Ban Specific
S1 TACT PB SWITCH

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Group 4: Low pass filter
When win ing the toroi cores, remember that one pass of
wire through the center of the core is one turn. Also try to
keep the wire snug to the outsi e of the core.
T2 is a bifilar woun transformer. This simply means you win
two wires on the core. Two colors of wire are use to help
i entify which is which. You can twist the wires together, or
simply lay them si e by si e as you win the turns. Wind 6
turns of the wire pair. When you are one, there will be a
re /green pair at the start an finish of the win ings. Reverse
the re an green wires on one si e of the core, so that both
en s of the re an green wires are opposite each other on
the core, as shown in the iagram above. Now trim back the
lea s an tin them. Insert the wires into the boar with the re
wires in the holes marke B B’ an the green wires into the
holes marke A A’, then sol er into place.
location value markings
C24 (All) .1 uF 104 Mono
T2 (All) See notes
40
C23 68 p 101 Mono
C30 330 p 331 Mono
C29 680 p 681 Mono
C28 330 p 331 Mono
L2 21 turns T37-2 (re )
L3 16 turns T37-2 (re )
30
C23 68 p 68 Mono
C30 220 p 221 Mono
C29 560 p 561 Mono
C28 220 p 221 Mono
L2 14 turns T37-2 (RED)
L3 12 turns T37-2 (RED)
20
C23 33 p 33 Mono
C30 150 p 151 Mono
C29 330 p 331 Mono
C28 150 p 151 Mono
L2 17 turns T37-6 (YEL)
L3 13 turns T37-6 (YEL)

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Final Tests
Your new rig is now just about rea y to use. All we nee to o now is peak the receiver trimmer an check for
transmitter power output.
For peaking the receiver trimmer, on 30 or 40 you can probably just connect an antenna up an peak the trimmer
for best ban noise or signal if someone is transmitting near the crystal frequency. On 20 an 15, you will probably
nee to generate a signal using your big rig, transmitting into a ummy loa . In this case, you just nee to use a
piece of wire or clip lea for an antenna on the DC rig an place it near the ummy loa . Don't plug in a paddle yet,
so you don't
accidentally transmit!
For testing the transmitter, you shoul have a ummy loa an Watt meter which is reasonably accurate at the 1
Watt level. Alternately, you coul use a 'scope if it has enough ban wi th or use a simple io e etector an volt
meter.
Connect up an antenna jack if not alrea y one, plug in hea phones, pa le an power lea s. Turn on power to
the rig. Put the keyer into “Tune Mo e”, using the function switch. This will allow you to toggle the transmitter on
an off. Toggle the transmitter on an see if how much power out you get. The amount of power will epen a lot
on supply voltage. With 13.8 Volts, up to 1 Watt an sometimes more is possible. At 12 volts, 700 mW is more
likely. Below 12 Volts, power output starts to rop quickly. The way the turns are space on L2 an L3 can also
make a significant ifference in the amount of power output, as minor changes in the in uctance can affect the
matching an power transfer. If your cores are woun with the turns more or less evenly space to start with, try
moving the turns closer together while watching the power output. Go back an forth between L2 an L3 until you
get the most power output you can.

2/14/2007 Page - 15
Trouble Shooting Guide
The most common reason a kit oes not work right is ue to sol ering issues. Therefore, the first thing to look for if
something oesn't work is the sol er connections. Look for sol er splashes that might be shorting two pa s
together an shoul n't be connecte . Also, for sol er which that might have stuck just to a lea an i n't flow into
the circuit boar pa , e.g., col sol er joints. Connections to the groun plane nee extra heat, so look closely to
these connections to make sure the sol er flowe into the hole. It’s also possible to have sol er on the circuit
boar pa , but it i n't flow aroun the lea .
The secon most common error is misplace parts. You may misrea a resistor color co e, or put it in the wrong
spot. The same goes with capacitors. So, if your sol ering looks goo , ouble check the parts placement.
Having an actual ba part is rare. It is possible to amage them though. The 2N7000 can be amage by static
ue to improper han ling an ICs can be amage if they are installe backwar s.
Some DC voltage levels are shown on the schematic, along with some wave forms. Note that the DC voltage
across R22, the crystal oscillator emitter resistor measures a lot higher than the base voltage, because of the way
the DVM respon s to the superimpose AC RF voltage.
Low Audio
The DCxx au io output is a equate for most hea phones especially the higher impe ance versions. If you are
experiencing low au io try a ifferent hea set. Those with the highest sensitivity ratings are the best.
If you still fin the volume too low, you can a a simple au io amplifier. Several circuits an kits using the popular
LM386 ICs can be foun on the internet.
A mini au io amp, 2cm x 2cm x 10mm, assemble an teste with 2.5 inch attache lea s is available from
W5USJ. This amp can be attache in place of R6, 10 Ohms, or in series with the hea phone jack using suitable
connectors. For more etails, visit: http://www.w5usj.com/miniau ioamp.html, email [email protected].

2/14/2007 Page - 16
aking Contacts with a Fixed-Frequency — Direct-Conversion Rig
Making contacts with this type of rig can be a challenge, but its not impossible. In fact, it can be a lot of fun an
satisfying. Just remember, it’s easier to have stations come to you. The reason for this is because the receiver will
hear stations on both si eban s, you on't know which si e ban your hearing them on. They coul be on your
transmit frequency of 7.040 or own at 7.039. Also, although the au io ban pass filter a s some selectivity, it’s
har to tell how close to your operating frequency they really are; especially if the station is pretty strong. You
coul be hearing them well, but your transmitting too far from their operating frequency for them to hear you. That
being sai , it can pay to try an answer a CQ you hear anyway, especially if they are signing QRP or QRPp. Then
you pretty much know they are on 7.040 an some operators actually use RIT to tune aroun a little for answering
stations. Or they coul be using one of these rigs or a Rock-Mite.
It also helps to carefully pick the time of ay an ay of the week to operate this rig. You want to pick a time of ay
an ay of the week when the ban isn't overly active. Contest weeken s an early evening prime time are out.
Goo times are Sun ay afternoon or evening, mornings, afternoons an late evenings uring the week.
Keyer Operation
The momentary switch is use to access three keyer functions, spee , tune mo e an iambic A/B selection.
Clicking an hol ing close the switch for various lengths of time access these functions.
Changing Code Speed
Keying spee can be selecte from about 7 to 30 wpm, in 1 wpm steps. Momentarily click the switch close until
the letter “S” is hear . Tapping the ash pa le increases the spee an tapping the ot pa le ecreases spee .
A ot will soun at each co e step. The letter “I” will soun when the upper or lower spee limit is reache . Co e
spee mo e will automatically exit if neither pa le is close for about 1 secon .
Tune ode
This mo e allows you to toggle the transmitter on an off, using the pa les. This frees up both han s to fi le
with an antenna tuner. To access tune mo e, click an hol close the switch until the letter “T” soun s. Tapping
the ash pa le will toggle the transmitter on an tapping the ot pa le will toggle it off. To exit tune mo e, click
the switch again.
Iambic A/B ode
The keyer uses iambic B mo e as the efault. This can be change to A mo e by clicking an hol ing close the
switch until the letter “A” soun s (about 2 secon s). This change isn't remembere by the keyer chip, so it has to
be change each time power is cycle . In either A or B mo e, hol ing close both pa le will pro uce alternating
ots an ashes. In B mo e, provi e the pa les are not release before the en of the inter-element space, an
extra ot or ash is a e to the en of the string.
Straight Key ode
If a mono plug is in the pa le jack at power up, the keyer will go into straight key mo e. In this mo e, there is no
nee for the function switch, so it is isable .

2/14/2007 Page - 17
How it works
Receiver
Signals from the antenna first travel through the transmitters low pass filter. It then passes through a T/R QSK
switch comprise of two, 2N7000 mosfets. During receive, Q9 is turne on an Q8 is turne off. This allows the
signal to pass into the link coupling into the front en tune circuit. During transmit, Q9 is turne off an Q8 is
turne on, isolating the transmit signal from the receiver. Q7 is use as an inverter, as Q9 an Q* nee
complementary logic signals.
The tune input circuit is connecte to a j-fet amplifier to isolate the mixer from the antenna an to provi e some
gain. The 10 ohm resistor in the Source lea prevents VHF oscillations. The output of the amplifier is then couple
into the mixer using a transformer woun on a small balun core. The mixer is an analog multiplexer. The analog
switches in the multiplexer connect the output loa resistor across the secon ary of the input tune circuit at the
LO frequency rate. On each half cycle, the phase of the input signal across the loa resistor is switche . This
pro uces the mixing of the LO signal an input signal, pro ucing an au io beat note at the loa resistor. Note that
there is no bias voltage on the analog switches. Biasing the switches to ½ the supply voltage woul improve the
mixers' ynamic range, but was foun not to be necessary. Any signal strong enough to overloa the mixer with
out bias, woul “blow your ears off”.
A high gain, ifferential input au io amplifier is connecte to the mixers' loa resistor. This stage provi es most of
the gain for the receiver. A pair of back to back io es across the amplifiers fee back resistor limits the peak to
peak output of the amplifier, to offer some hearing protection from strong signals. These io es also re uce clicks
create by switching transits when switching from receive to transmit an back again.
The output of the first high gain au io stage is then route though another analog switch, again without bias, for
au io muting uring transmit. The signal then goes into an au io ban pass filter stage. This filter has a Q of 8.
However, since only a single stage of filtering is provi e , the filter isn't as narrow as a Q of 8 woul imply when
strong signals are present. The output of this filter rives the hea phones. A 10 ohm resistor helps keeping the
amplifier stable when riving the relatively low impe ance of hea phones an the .001 cap across the output helps
keep RF, which might be picke up by the hea phone lea s, out of the amplifier. The NJM4456 op amp use has
a high current output, so has no trouble riving hea phones.
Oscillator and Transmitter
A classic Colpitts crystal oscillator provi es the Local Oscillator. During receive, Q4 is turne on, which isables
any effect C34 has on the oscillator frequency. During transmit, Q4 is turne off, allowing C34 to increase the
oscillator frequency. C34 is use to set the transmit frequency about 600 Hz higher than the receive frequency,
provi ing proper T/R offset. When going from receive to transmit, the keyer chip will first mute the receiver an
shift the oscillator frequency before enabling the transmitter output. When going from transmit to receive, the
transmitter is first turne off, then after a elay of about 5 ms, the receiver is un-mute an the oscillator frequency
shifte .
Q3 buffers the LO output signal in or er to rive the PA. This stage is turne on an off by the keyer chip, with the
help of Q5. R23 an R25, in combination with C35, form an R/C time constant which causes the output of Q3 to
ramp on an off in about 5 ms. This provi es wave shaping to the output signal, as to eliminate key clicks.
The output of Q3 in turn rives the PA stage, a 2N7000 MOSFET. Dio e D10 across the gate acts to ouble the
rive voltage by charging the coupling cap, C27 on negative cycles. This ensures there is enough rive voltage to
turn Q2 reasonably well on. The output of the PA, Q2 is couple to the low pass filter through a bifilar woun
transformer. This provi es some impe ance matching an increase power output an efficiency. Capacitor C23
tunes the L3 coil to the secon harmonic, which forms a trap. This ensures the spurious output of the transmitter is
well below require FCC limits. It also improves PA efficiency an power output.
A 78L05 regulator, U4, is use to supply the require voltage for the keyer chip an mixer. It also is use as a bias
voltage for the au io amplifier op-amp an supply voltage for the Q10 preamp an U2 mixer.

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