The DSW-20 is a compact lightweight portable single band transceiver designed and marketed by Dave Benson of Small Wonder Labs as a follow-on to his 40-40 and SW+ series of kits. Unfortunately, due to component supply difficulties, Dave stopped producing this kit, so it rapidly became a "classic" QRP rig. The rig is somewhat unique in using a DDS instead of a normal linear VFO. Also a PIC provides a built-in keyer and audio frequency annunciator.
The kit was quite easy to build and the alignment couldn't be easier.
It worked first time and gave a power output of just under 2 watts at a total input current of 350mA.
I mounted the PCB in the supplied custom case, which results in a portable rig measuring 4.24" square
and weighing about 12 ounces.
A DL-SWR meter has been added, the front panel bicolour led displays the SWR. The DSW20, 1.1Ah GellCell battery, ear-buds, Whiterook paddle and half-wave antenna and ATU all fit inside a small zippered bag which slips easily into my rucksack for portable operation. This is the ideal single band rig for "Adventure Radio".
I have made some modifications. Firstly, the driver emitter resistor was replaced with a trimpot as recommended by K5DH to optimize the power output, but the modification didn't seem to be too effective, so I changed the resistor from 51 to 39 ohms. The supplied PA transistor is a 2SC1947, a 12 volt device which is somewhat fragile under high SWR conditions. After having to replace the PA after SWR problems, I substituted a 2N3553 instead. This is a 28 volt transistor which is more robust and also considerably cheaper than the original 2SC1947, although it is not so efficient at low battery voltages.
Dave later resurrected the DSW as the DSW-II, with some improvements and greater power output from a better PA transistor.
I ordered a 40 metre kit and found it easy to build with only 1 toroid to wind and alignment consisted of just one coil to peak for maximum received signal.
Whilst the bare PCB was on the bench being aligned by peaking for maximum strength of received signals on 40 metres, I heard ZB2FK, so plugged in a paddle and called him.
I was very impressed when he came back after my first call and gave my 4 watt signal a RST579 report.
Since completion, the rig has been mainly used portable and gives a respectable 3w output when using 10 NiMh AA batteries.
I did experience one problem with the rig when a high swr antenna caused the clamp zener on the PA collector to go short-circuit and burnt up the etch and PCB around the PA section.
After repairing the damage, I used a higher wattage zener as a replacement instead of the puny one originally supplied.
I also rebuilt my ATU for the end-fed wire to use a LED SWR bridge that presented a constant 50 ohm load to the PA when tuning the antenna.
The only modification I've made to this rig was to replace the original PIC with a DSWK IC from Jackson Harbor Press, which provides an enhanced keyer.
Unfortunately, this very useful product was also discontinued and in 2013, Dave Benson wound up Small Wonder Labs and also closed the website, ending a valued contribution to QRP enthusiasts.
40m portable QRP station using DSWII
40m portable station packed in camera bag, with 40m Dipole and 14ft Crappie Rod
Contents of bag include the DSW-II, Palm paddles, earbuds, logbook & battery pack
|AE5X's Website||-||DSW Modifications|
|Adventure Radio Society||-||DSW20 Lab Test|
|DK5RK's Website||-||DSW20 Revue|
|Jackson Harbor Press||-||DSKW, an updated PIC with memory keyer functions|