The ARS QRP Lab Reviews the Wilderness Radio SST Transceiver
The ARS Sojourner
Our SST came from Wilderness Radio. You can find basic information for the SST on the Wilderness Radio web site, http://www.fix.net/jparker/wild.html, and we won't repeat it here.
Radio design is the art of compromise. Almost every virtue of a design has its offsetting cost. In these lab reports, we attempt to shine light on how these compromises have been struck. It is endlessly fascinating.
Feeling a little tangled up with knotty technical questions? Many of our graphics have this portrait of a fellow electronics adventurer. Just click, and you're on your way to helpful background material.
Transmitter Tests
Power Output
Rated output for the SST is 2 watts depending on frequency. Our sample produced 2.1 watts with a 13.8 volt power supply and 1.9 watts with a 12 volt power supply.
Power Requirements on Transmit
With a 13.8 volt power supply, our SST drew 307 mA with 2.1 watts of RF output. With a 12 volt power supply, our SST drew 286 mA with 1.9 watts of RF output.
Spectral Purity
FCC regulations require the spurious emissions from a 2 watt radio to be at least 30 dB below the carrier. Our sample just barely met this requirement.
We performed these tests with a Tektronix TDS 380 scope with Fast Fourier Transform capability. Follow this link for an explanation of the FFT approach, as well as some help on reading the annotations on the graphs.
Here is the link to the spectral purity graph for our sample.
Introduction to Receiver Tests
Many of our receiver test reports use bar charts that compare the unit being reviewed to a number of other HF transceivers. Please read this brief explanation of the purpose and layout of these charts.
Receiver Tests—When No External Signals are Present
Tuning Range
Our sample tuned from 14.052 to 14.062 MHz. We understand that many owners of SSTs have successfully experimented with the tuning range of the VXO, and we assume that it would be possible to tweak our sample so that the QRP calling frequency of 14.060 would be closer to the center of the tuning range.
Stability
As you would expect from a crystal-based oscillator, the stability of our SST was excellent. Please follow this link to a graph of the radio's stability during the first 30 minutes of warm up.
Spurious signals
There were no birdies in our sample.
Power Requirements on Receive
Our sample drew a remarkably low 15.5 mA on receive with a 13.8 volt power supply, and the same amount with a 12 volt power supply.
Receiver Tests—When One External Signal is Present
Minimum Discernible Signal
On 14 MHz we measured an MDS of -144 dBm, in a 6 dB bandwidth of 150 Hz. This is an extraordinary level of sensitivity, and at first we were concerned that our testing may have gone awry. However, we double checked our results by measuring the noise figure of the SST, and our MDS measurements appeared to be correct.
Please keep these cautions in mind:
- MDS improves as the bandwidth becomes more narrow. Our SST had a very narrow IF and AF response (150 Hz), so we can anticipate that its MDS would look better than normal.
- On 20 meters, sensitivities this high are not generally useful, because the typical external noise will be higher than the internal noise of the receiver. In fact, sensitivities this high will be often harmful, because they will cause the external noise to be amplified.
- High sensitivity is often accompanied by poor dynamic range.
Please follow this link for comparisons with the MDS of other HF radios.
Phase Noise
The SST had excellent performance with its phase noise, which is another advantage of a crystal oscillator. We measured phase noise of -138 dBc/Hz.
Please follow this link for comparisons with the phase noise of other HF radios.
IF Rejection
Our sample had IF rejection of 94 dB. Please follow this link for comparisons with the IF rejection of other HF radios.
Image Rejection
Our sample had a disappointing image rejection of 30 dB. Please follow this link for comparisons with the image rejection of other HF radios.
Audio Output
Using the standard ARRL test tone of -70 dBm, we measured total harmonic distortion of just 0.50 percent. The AGC was strongly limiting the receiver's gain, and the audio in the headphones was only moderately loud.
Receiver Tests—When Multiple Signals are Present
Selectivity
We measured a 6 dB IF and AF response of only 150 Hz, even though our sample had been modified (in accordance with the Wilderness Radio manual) to increase the IF filter's bandwidth. You will find interesting information about the width and shape of the SST's IF and RF response in this AF spectrum analyzer graph.
Blocking Dynamic Range
Our SST had a blocking dynamic range of 103 dB. Please follow this link for comparisons with the blocking dynamic range of other HF radios.
Third Order IMD Dynamic Range
In one of the more important tests of our review, we measured a worst case third order IMD dynamic range of 81 dB. Please follow this link for comparisons with the third order IMD dynamic range of other HF radios.
Third Order IMD Intercept Point
We calculated a worst case third order intercept point for our SST of -22.5, which is quite low. Please follow this link for comparisons with the third order intercept points of other HF radios.
Second Order IMD Dynamic Range
Although this test was ignored in earlier times, it is now receiving increasing attention. Our sample had a very good second order dynamic range of 99 dB. Here is the link for comparisons with the second order IMD dynamic range of other HF radios.
Second Order IMD Intercept Point
We calculated a second order IMD intercept point of 54 dBm. Please follow this link for comparisons with the second order IMD intercept points of other HF radios.
In-band IMD
Another test that hasn't received much attention. But we have a hunch it will be important for the low power community, because it may shed light on the superhet/direct conversion trade offs, and because it may help us quantify the poor audio we see in some simple transceivers.
In the SST, the test signals generated a remarkably clean response (although the audio level seemed low). Here is the link to an AF spectrum analyzer graph. For purposes of comparison, here are links to the AF spectrum analyzer graphs for two much more expensive and complex radios, the Yaesu FT-1000 MP and the Elecraft K-2.
Conclusion
The SST is an outdoor workhorse, and is probably the most currrent-efficient kit transceiver you can build. It is an impressive illustration of how much can be accomplished with a minimum number of parts.
On the other hand, its performance specifications are a mixture and the best and the worst. If you sometimes need to cope with the big guys, the SST may not be the best choice. But ff dynamic range isn't important to you, and you want a lean hip pocket machine, then this radio may be perfect.
Here are some important links:
The lab's goals and equipment.
