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Numbef" 20 on your Feedback c.rd CW Transceiver for 20 Meters Get on this favorite OX band. Adapted from G-DRP Club Circuit Handbook A re you ready for the challenge of 20m QRP? Want the added enjoyment of rolli ng your own rig? If so on both COUnlS , then check out the following home-brew project! This interesting little project uses componcnrs ranging from tubes to ICs. Hybrt d Some of the modules used to build this rig were removed from existing equ ipment ; others were built specially. This explains the different devices for the TX modulator and the RX mixer, the option of two carrier injection oscillators (CIO) , and the SSB-type filter instead of a CW filter. Clrcun Descriplion The Colpitts VFO circuit, Figure I, has gate clamping to improve stability . It' s followed by two buffers , the second providing by Frank Lee G3YCC individual outputs to the TX and RX. A RIT circuit operates on receive. You must set it up correctly when you fi rst align the rig (see instructions below). Build the VFO in a stout metal box, with care for mechanical rigidity. The RX front e nd uses 40673 dual -gate MOSFETs (see Figure 2). The tuned circuits are peaked to the center of the CW band with trimmers. Coil winding details for the VFO and other stages appear in the respective figures. The mixer output is link-coupled to a KVO 9 MHz SSB filter , whose output is amplified by an SL612 IF amplifier IC (see Figure 3). The product detector uses two BC 107 tran sistors. Carrier reinjection is from a crystal oscillator using the USB crystal supplied with the KVG filter. Figure 4 contains two diagrams: an FET oscillator and a PNP bipolar oscillator. You can use either, or you can alter the circuit pola rities to suit an NPN transistor. An LM380 Ie would work fine he". TheTX mixer is an MOIOS (Figure 5), fed from the VFO and the lowe r sideband carrier injectio n oscillator. (You could probably usc the less expensive 40673 as a mixer.) The mixer output is applied to an SL6IOC RF amplifie r. then to a FET which drives a 12BY7A PA similar to that in the well-know n " Tucker Tin,. circuit. I tried to use a transistor PA, but had troubles with it (likely due to my lack of experience in transistor PA design!). A simple diode/meter circuit measures relative power output (see Figure 6). Sidetone is provided by an NE555 circuit (see Figure 7). Send/receive sw itching is by means of a a-pole change-o ver relay controlled from a Ll • 30T_. 34 SWG ON 1/4,n. 0 SLUG -TUNED FORMER " 0 ., ~6 _8 V l!l < 5.1 MHt j ZEN " 4 ~ ~p F " " ~ 30 p F ,F +12 V 4 REG. " 1°' 1°' r. BCIDa ~ IN9 14 2N 38 19 BC I Qa '" " 'OK V" 0I,5C ; :::: ~ 8 0 " , r. 0.01 ~ 0,01 I ,I Rx MIX - DI SC RFe '" I ,I T. MIX ""lOOT 30S WG T68 0PF 470 ON IW RE S. 3.3K Figure J. Colpitts VFO c;rcuit. L I, L 2' 251. 30 5WG, ON 1/4 i n SLUG' TUN ED. LI NKS 4 T. L3' 30T. 30 SWG 1/ 4 ill. 0 FORMER. Utfl( 4 T 1501( VFO " 47'F+ 4 0 6 73 4 0 6 73 " 0 ,,;;r S " ee0 L> + 1 2 V~(RI I 47pF r '-F STR" • 150 1< " * 25 PF *IOnF * IOOnF ANT, ....., -::~ 25 pF ::::; tOOnF 150K RLA , '" " 0 lOOK 2.71< ; ~ 2 0nF Figure 2. The receive from-end. The associated tuned circuits are pealed to the center o/the CWband ""ith trimmers. 73AmateurRadio • June, 1989 65
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