DSW-20 Transceiver by Small Wonder Labs

The DSW-20 Kit by Small Wonder Labs:
My experiences (DK5RK)

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The DSW-20 is a monoband Kit provided by Small Wonder Labs. This small company is maintained by Dave, NN1G. It is a superhet TRX with an IF of 5185 kHz using the SA612 mixer cicuits. The peculiarity is the PIC-controlled DDS VFO. A lambic keyer is included as well as the QRG readout by morse code. The whole TRX is only 7x10 cm in size and needs just 40mA in receive mode.

Technical specifications of DSW-20

RF Output power about 3 watts (see measurement below)
TX and RX range covers whole band
PIC-controlled DDS generation of RF
extreme stable VFO (see measurement below)
Size of PCB: 7x10 cm
Tuning speed adjustable to 50/200 Hz per step
RIT range: unlimited (but no frequency read-out for RX QRG)
Split operation possible
RX IF filter of about 500 Hz bandwidth at -6 dB (simple 3 crystal ladder filter) (see measurement below)
Power requirements: RX about 40 mA; TX at 12V: 320 mA (2.5W out) & at 13.8V: 410 mA (3.2W out)
Supply voltage 8-15 V
TX spurious emission at 2.5 W out < 30dB
IF rejection about 80 dB
Image rejection about 55 dB
Price at Small Wonder Labs: $95 (Sept. 2000)
Built-in Iambic keyer 5-50 WpM
Keyer options: speed, reverse, tuning mode (key down), straight key
Frequency read-out per morse code
No equipment needed for the alignment of kit
Other band versions available: 80m, 40m, and 30m

For the enlarged view of the schematics please click here: PDF file 180 kB.

This is the kit as arrived (cost about $100). More than 200 parts.
The board as supplied is not entirly emty: The DDS and a few SMD parts
are already mounted (below OSC1).

All parts in place after about 8 hours of soldering. It worked perfect after
supplying voltage!
The "On-the Air-Test" after assembling: The first QSO was done using my
vertical with Costy in Constantza (YO4CSE). Received RST: 589.

The case is a standard eloxised Al box for the "Euro-PCB" format. It can
be obtained by "Conrad Electronic".
There is still enough air in the box for easy wiring.

An accumulator of a hand drill is sufficient for many hours of operating
the DSW-20 due to its low current in receive mode (I=40mA).
The built-in iambic keyer makes the setup of the complete shortwave
station very easy. You need a paddle, earphones, antenna and a
power supply.

Output power is measured as a function of supplied voltage. A reduced value of R20 gives a higher output at low voltage. Note that the PA transistor isn't cooled at all. Do not try to get more than 3 W out.

The stability of the TX signal has been recorded after applying voltage, and after switching on a strong infrared lamp in a distance of about 30cm (open case). The DSW-20 is extremely stable in both cases! The QRG reading auf the TRX gave 14060 kHz.

The overall bandwidth was measured with a noise generator at the antenna input and the computer soundcard using the program "Gram". The 6dB bandwidth is about 500 Hz with the maximum sensitivity at 800 Hz. The schematics of a suitable noise generator is here (refer e.g. to the "Antennenbuch" by Karl Rothammel).

Again the overall bandwidth measured with commercial equipment using noise generator and Spectrum Anylazer SNA-2 (Wandel & Goltermann).

The spectral purity of the transmitter was found to be excellent when transmitting at 14060 kHz with Pout=2.5 W. Side peaks and first harmonic are suppressed by at least 60 dB. Higher harmonics are < -70 dB (up to 150 MHz). Signal was analyzed by the Spectrum Anylazer SNA-2 (Wandel & Goltermann).

This is the kit as arrived (cost about $100). More than 200 parts.	The board as supplied is not entirly emty: The DDS and a few SMD parts are already mounted (below OSC1).
All parts in place after about 8 hours of soldering. It worked perfect after supplying voltage!	The "On-the Air-Test" after assembling: The first QSO was done using my vertical with Costy in Constantza (YO4CSE). Received RST: 589.
The case is a standard eloxised Al box for the "Euro-PCB" format. It can be obtained by "Conrad Electronic".	There is still enough air in the box for easy wiring.
An accumulator of a hand drill is sufficient for many hours of operating the DSW-20 due to its low current in receive mode (I=40mA).	The built-in iambic keyer makes the setup of the complete shortwave station very easy. You need a paddle, earphones, antenna and a power supply.