Small Wonder Labs SW-40, -80, -20 QRP Rigs

Small Wonder Labs

Dave Benson — an amateur radio operator and radio engineer — for several years operated a home-based business, Small Wonder Labs.  He designed, tested, and sold a number of kits for low-power operation.  I purchased and built several of his SW-series rigs.  The SW+ series rigs are available for 80, 40, 20, and 30 meters.

My Experience with the SW+ for 40 Meters

I built Small Wonder rigs for 80, 40, and 20 meters.  Here I will describe only the SW-40 as the rigs are quite similar.

I ordered my SW+40 on 19 January 2010 and received it two weeks later, on 30 January.  The kit arrived in the mail at the beginning of a HUGE snowstorm.  When I went to the mailbox, the wind was blowing from the north — across the Potomac River — at 20 MPH with gusts to 30 MPH and snow was falling at the rate of an inch an hour.  I brought the kit into the house, ate lunch, then started assembling the rig.

Assembly was straightforward.  Dave includes with the kit a CD that has the latest version of the assembly instructions.  Also, you can print the instructions from his website.  I printed extra copies of the parts list and the parts placement diagram to use while building the rig.  As I placed parts on the PC board, I checked them off on the parts list and the parts placement diagram.

Total construction time from opening the box and dumping out the parts to putting the rig on the air was six hours, including an occasional break.

I had no problems in building or tuning the rig — it worked perfectly the instant power was applied.

Here are some photos

First is a picture that I copied  from the Small Wonder Labs website showing a close-up view of the PC board.


Note the four crystals lined up from right to left down the center of the board.  Three of these form a crystal filter for the receiver that makes it quite sharp and knocks out most interference when the band is crowded.

Here’s a picture of my SW+40 laid out after I tested and tuned it.

bare sw-40 2

Here is the SW+40 with all connections laid out on my operating table.  The red and black lead from the left is power.  The red-yellow-orange leads that go to the small knob on the left are the volume control.  The big knob in the front center of the photo is the tuning control.  The small PC board is a FreqMite frequency counter from SWL — this is a separate item, not part of the SW+40; I wired it into the SW+40 to give me an audible readout of the operating frequency.  The green-yellow-orange lead on the right goes to two jacks — key and headphone.  To the upper right of the SW+40 is my KK-1 straight Key from American Morse Equipment.  To the right of the key is a big silver connector — this is the antenna connector.  The tiny silver object to the right of the FreqMite is the switch that activates the FreqMite.  I laid out the rig in this configuration to test it and tune it.

Tuning took only a couple of minutes.  As soon as it was tuned, I made two contacts with the rig, one in central Tennessee and one in New Hampshire.

Specs for my SW+40

Frequency coverage:  7026 – 7068 KHz.

Power output:  1.25 watts.  The rig is capable of putting out 2.5 watts and output power is adjustable from under 1 watt to 2.5 watts.  I set mine at 1.25 watts.

Tuning:  Tuning is accomplished by varying the voltage across a varactor diode.  The big knob in the photo above is attached to a 100K ohm potentiometer, which is the tuning control.

Here are more details from the SWL website:

  •  Single-board transceiver, 2.8 x 4.0″ (7 x 10.1 cm)
  •  Commercial-quality board, masked and silkscreened
  •  True VFO: 35-40 kHz coverage
  •  Superheterodyne design, with crystal filtering
  •  Quiet solid-state T-R switching (QSK)
  •  Output Power Adjustable- 2.5W max.


Although I have had the rig on the air for only a few minutes before preparing this article, I can tell that I will enjoy this rig and it likely will be my main QRP rig.  The receiver is very sharp and sensitive; the rig is small and has low power requirement; and, all-in-all it’s an excellent piece of equipment.

Important:  Frequency readout for the Small Wonder rigs

Small Wonder Labs produced a kit, the FreqMite.  This kit consists of a programmable frequency counter and an audio output that sent Morse code numbers corresponding to the frequency on which the radio was operating.  I installed the FreqMite into my Small Wonder Labs rigs and found it to be a very useful addition.  Here’s a page describing the modification.