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: Number, on yourFMdback eard QRP CW Transceiver r-------------, 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\' .., " 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 :- --, you m ight wa nt 10 T wo OIl'Wf" "u... "'...._ oc OO .~ .(l) ~ .- .".(" ""u..• ' .. At'" U ' '" AuOIO "' ~ ce-ce. "!. " A . "OlEtT"," O'.OA AUOIO "' I"L I "' ,..TU A"'Th.... TA •., ~ .''''(" ..: Spt:A"(" 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- _. -~I . [= 6'>--- UOfO -l n- - • • • • •• 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! ~,~ ~E '........OIO BOTTOOO '1 ( * 1+'\ 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
CI C2 + V REG 02 +12 V C4 01 , C. c 0 2 J CO , I-' , r-' 01 s b's CIO D2 0' RFCI 04 O' L3 L4 J3 ANT rl * C1 3 O. ;rCII os R71 Cl2 + V REG r 0 10 Oil +V REG ~7 I C'!:> ZER O + 12V 0 12 014 0" O' DS O~ ;;;C2 0 ~~ I R I 9~' OIS 0 4 , RI6 ;;kCI. ,It Clea t ;};C17 TO U2 ~ C44 D' OUT: + V REG + 12Y FO~T3 I . T4 .' • I'd, , 2 • +~ V ~ t..l C ·* C26'iA' '. \ ~H-"'-+--.",*" dr ',J, J C27 F,'" 0 0 ;1;C' O RFC2 024 02. 0 2. + 12Y FROM y, F.O. t 6 * C2e 02' 0 2 S DIO C'4 C3S " 0 ' 2 +12V DII " 0'0 FROM Q6 040 - 041 S IOETONE B L.....o 7 6 I ~ 0" 2 • UI + 12 Y 033 0'4 0'. ,J; "2"""""""T3 " 'I~ C4 1 C42 SIDETONE R4 2 VO LUME ;tc,. C4' Figure 3. Schematicfor ,h~ QRP transceiver. 73 Amateur Radio • June. 1989 21
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