Wilderness Radio SST 

The Wilderness Radio SST (Simple Superhet Transceiver) is a compact single band CW transceiver that covers a portion of either the 40, 30 or 20 meter bands. It is a very easy project to build because of it's simplicity. There are fewer parts in the SST than most other kits, however despite its simplicity, it is an excellent on-the-air performer.

The kit uses standard through hole parts (no surface mount parts) and a high quality PC board. It includes a predrilled but unpainted aluminum case.

The SST receiver is a single conversion superheterodyne with a three pole crystal filter. The local oscillator uses a varactor tuned VXO (Variable Crystal Oscillator) instead of a VFO, which results in excellent stability in varying temperatures. The transmitter produces between 1 and 2 watts of RF output, depending on supply voltage.

Because the SST uses a VXO for the tuning, only a portion of the band can be covered. Wilderness supplies two tuning varactors with the kit and the builder can choose either (or both) varactors to customize band coverage desired. Some builders add switches to their rigs to select the varactors for maximum band coverage.

Note that the VXO crystals supplied are off the shelf computer crystals and you may possibly not get coverage of all of the QRP portion of the band. In the WØCH 20 meter SST, only the smaller value varactor was used and this resulted in a band coverage of 14054.5 to 14062.5 kHz. The larger value varactor would tune lower in the band, however it reduced the coverage in the QRP portion of the band above 14060.

The tuning control is a single turn potentiometer, however this works fairly well with the limited tuning range. The builder must provide the dial calibration. Because of the simple design, there is no provision for RIT (Receive Incremental Tuning).

The WØCH 20 meter SST in the photographs has been modified with the addition of an internal TICK keyer. The keyer was constructed "Manhattan" style on a small piece of PC board material and mounted on the rear of the chassis above the antenna and power jacks. The red push button seen on the front panel is the TICK keyer programming button. This single button is used to set the keyer speed and mode.

Inside the SST, showing the TICK keyer modification

The SST uses very little power. The receive current drain (including TICK keyer) on the WØCH rig is 20.3 mA. The key down current is 325 mA for 2 watts of RF output power from a 13.5 volt DC supply. When powered by 8 AA batteries, the RF output is about 1.5 watts.

The SST is probably one of the smallest transceivers available. The case measures 3.4 inches wide, 1.5 inches high by 3.75 inches deep. The rig as shown weighs 7.5 ounces.

Because of the very stable VXO, low power consumption and small size, the SST is a favorite among backpackers and mountain climbers. I use the SST in the photograph for a trail friendly package where the entire station, including battery, antenna and carrying case, weighs less than 2 pounds.

 

 

Rear view showing the added paddle jack above the standard key jack

The SST is available as a kit from Wilderness Radio (URL below). There are four frequency ranges available The approximate frequency range of each model using the two provided tuning varactors is shown below:

BAND
Using MVAM108
Using MV209

40 Meters

7.030 - 7.040
7.035 - 7.045

40 Meters Novice

7.105 - 7.115
7.110 - 7.120

30 Meters

10.095 - 10.110
10.105 - 10.120

20 Meters

14.040 - 14.055
14.050 - 14.060

Builder's Notes:

I discovered that the LM386 audio chip would howl loudly when 300 Ohm headphones were used on the rig. The howling was less pronounced with a 20 Ohm headset. The howling was stopped by adding a 10 Ohm resistor across the 1 K volume control (from "hot" to ground).

A further increase of AF amp stability was gained by adding a .001 uFd RF bypass capacitor across the headphone jack.

The 20 meter tuning range using the MV209 varactor was 14054.5 to 14062.5 kHz, slightly higher than the range specified in the instruction book. Since there is QRP activity above 14062.5 during contests, an additional couple of KHz range would be desirable.

TICK Keyer Modification:

The TICK keyer uses the TICK-1 chip. It is powered from the 12 power line through a 78L05 regulator chip. A 20K trim pot is used as a sidetone level control with the wiper connected directly to the headphone jack. The paddle jack was mounted immediately above the straight key jack. The programming push button was installed on the front panel above the headphone jack.

SST Links:

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Updated Sept. 12, 2004