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QRP CW Transceiver
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A great little do-it-yourselfDC rig
for the 30 or 40 meter band.
by Bruce Auld NZ5G and Bill Heishman N5HNN
M
uch of the fun in amateur radio comes
from having " done it yourself." In
my search for a projectthat would yield a un it
with satisfy ing performance. I found two
common problems: The writer assumed too
much knowledge on the pan of the builder.
and the pans we re not widely availabl e.
Thi s project is different. The builder gets a
running stan in home-brew with something
that will del iver plenty of fun and performance,
and the pans are available 10 anyone
with access to a Radio Shack store.
This is a 3-Wan, single ci rcuit board, 40 or
30 meters. VFO-controlled CW transceiver,
Photo B. Top ~ 'ie l\'
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I
featuring a direct conversion receiver
with aud io filtering , Receiver Incremental
Tuning (RIT), and speaker level
audio volume. It is based upon the
classic design by W7EL with a few
alterations. My partner (and technical
genius) in this project, Bill Heishman
N5HNN. and I put it together as a cl ub project
for the Arlin gton Amateur Radio Club.
T heory of O per ation
The d irect conversion receiver and transmitter
described in this article are quite
simple. Mueh of the technical Information
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Figure I. QRP transceiverflowchart. Note callouts (Ql . Q4, U2, etc.]
which help you locate that section af the transceiver on the schematic.
20 73AmateurRadio " June, 1989
ofthe inside ofthe QRP rig. Note the double-sided
PCboard. for improved grounding. The VFO RFshielding (upper left)
is easily tack-soldered on.
know. and the rationale
beh ind specific
design choices, has
bee n e xpe rtly de ­
sc ri b e d by R o y
L e w a l l e n W 7EL
(" A n Optim i zed
QRP Transceiver."
QST , August 1980).
The best way to get
over the initial fright
oflooking at the schematic
dia gram is to
break t he c ir c u it
down into modules
and see how simply
the modules connect
to one another. 1beIJ..
retically. the modu les
cou ld be built sepa-
_.
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[= 6'>--- UOfO
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•
•
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Photo A. Front panel of the QRP transceiver. The
Receive tncrememal Tuning (RfT) control allows JOU
to adjust the rect-i)" frequency without changing Jour
transmit frequency.
'''' T(G"AT(O C' .CUlT~
TOO' y,n.
rarely and then interconnected with a few
cables. For simplicity, all the modules are
located on a single board.
Refer to the flowchart and schematic dia ­
gram. Figures I and 3. Beginning with the
transmitter. the transmit frequency is genetared
by Q I and irs associated components in
the VFO. The buffer. Q2, isolates the oscillator
from the other circuitry to help keep the
VFO stable. Q3 builds up the signal toa more
usable level. The driver, Q4, amplifies the
signal. The final , Q5 . amplifies it to the 3·
Watt level.
You key the transmitter by turning the
power to the driver on and off , using Q6 as a
s.....itching transistor. Select the frequency by
varying the luning capacitor, C2. The transminer
is thai simple!
The VFO frequency feeds into the d iodering
mixer, and is mixed with the incoming 7
o r 10 MHz signal. The diffe re nce , o r
" product." is the aud io frequency you eventually
hear from the speaker. That is why this
stage is also called a " product detector." All
the circuitry after the mixer builds up the
audio signal to speaker level: Q8 preamplifies
the signal a little . U2 is an audio filter that
attenuates the audio signals above about 700
Hz, and U3 amplifies
the signal from the
audio filter to listening
level. That's it!
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Figure 2. Base diagrams for the semiconductors
used in this project.
SpecifIC Rig
Components
VFO: The VFO is
a simple , well-known
Hanley ci rcuit. Drift
is minimal. Frequency
generation is mostly
dependent upon the
Ll and ca pacitors
C I-C4, When plotled
out. these components
yield the VFO' s
operating frequency.
C2 is the main tuning
capacitor, and C4 is a
miniat ure trimmer.
Thi s is important for