Small Wonder Labs SW20+

The SW+ series of single band CW transceivers were designed by Dave Benson K1SWL, who sold thousands of these little kits under the Small Wonder Labs product name. Originally designed for the New England QRP club as the NE40-40, Dave updated the circuit and sold SW+ series kits for 80, 40, 30 and 20 meters (and perhaps a limited number for 160 meters). They were available as a board kit where the builder provides the case, controls and connectors, however a custom case which includes the controls and connectors was also available from SWL.

SW+ series transceivers use a single conversion superhet receiver based on the NE602 mixer chip. There is no IF amplifier stage however a second NE602 is used as a product detector. The 20 meter version uses a 9.0 MHz intermediate frequency and has a three pole fixed bandwidth crystal filter. The NE5532 audio amplifier chip is configured as an audio filter centered around 800 Hz to add additional selectivity. The audio output is designed for headphone operation.

The VFO uses varactor tuning and the builder sets the desired tuning range using fixed capacitors provided with the kit. The SW20+ in the photograph tunes from 14.033 to 14.066 MHz. A standard single turn potentiometer is used as the tuning control. See the link below for information on modifying the tuning range linearity for improved tuning in the QRP "watering hole" spectrum. The dial calibration on the SWL case is simply a series of dots, however the FREQ-Mite optional Morse code frequency counter is still available as a kit from the 4SQRP club. Receive Incremental Tuning (RIT) was also available as an option from SWL.

The SW20+ transmitter puts out about 2 watts of power but it can be reduced by adjusting the internal drive control. QSK and keying is very nice. The sidetone uses the transmitted signal as heard by the receiver but there is no provision for sidetone level adjustment. The SWL case uses a BNC antenna connector.

The photograph to the left shows the internal view of the SW20+ transceiver in the optional Small Wonder Labs enclosure.

The PC board is mounted in the enclosure on four nylon standoff posts. Most connections to the board are via wiring harnesses and plug-in multi-pin connectors. Only the antenna coaxial cable is soldered to the board. The PC board can be easily removed from the case for modifications or repairs.

In the photograph, the transmitter power amplifier stage is in the lower right corner and the receiver front end is in the upper left corner of the circuit board. There are five toroid coils to wind in the 20 meter transceiver.

Alignment is very easy as there are only a few tuned circuits to adjust. There is only one coil to peak in the receiver front end and only two tuned circuits to peak in the transmit bandpass filter circuit. The desired VFO tuning range in the 20 meter band is set by selecting a band set capacitor from a selection of eight values (included in the kit) to give the desired range. Some experimentation may be needed to select the value that provides tuning for the part of the band that you desire. My unit is set to tune from 14.033 to 14.066 MHz. I modified the tuning linearity of my kit to provide more bandspread near the QRP 14.060 MHz watering hole. More information on this simple modification is available here: SW20+ Tuning Modification

SWL's manual and building instructions were excellent.  Dave Benson no longer provides technical support, however he has the instruction manuals available on the internet. This rig was an excellent "first kit" for novice builders. A whole series of educational postings (called Elmer 101) based on the SW40+ (the 40 meter v archived from the QRP-L E-Mail reflector and are available on the Internet to assist builders. 

SW+ Series Links:

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Updated June 16, 2016