The ARS QRP Lab Reviews the Elecraft K-2 Transceiver
The ARS Sojourner
We've received valuable comments from a number of you. Thank you!
Our New Format
This report features our new grapically-oriented format. There is quite a collection of fascinating graphics hidden behind the upcoming links.
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.
The Elecraft K-2 Transceiver
The K-2 has received a flood of favorable commentary during the past half year, which it clearly deserves. Your author built K-2 number 218 and agrees that the K-2 is a stellar perfomer, reflecting the extensive operating experience of its designers.
If you decide to build the K-2, figure out how to beg, borrow, or steal about 50 hours of time. The manual is outstanding, and so is technical support (both from Elecraft and from fellow hams in the Elecraft mail list). But this is an ambitious project, and you will get a lot more pleasure and knowledge from it if you can set aside some quality time.
The K-2 breaks new ground for QRP transceiver kits in many ways. One of the most dramatic is the degree to which the radio is controlled by firmware. This is a double-edged sword. It is fascinating to see what can be accomplished by a firmware genius like Wayne Burdick, N6KR. On the other hand, sometimes you won't be able to peer under the hood. Aspects of this radio will remain inscrutable.
Elecraft's web site contains a complete listing of the radio's specifications, options, and prices, and we won't repeat them here.
Transmitter Tests
Power Output
Rated output for the K-2 is 10 watts. Our sample produced about 11.5 watts on all bands.
Power Requirements on Transmit
With a 13.8 volt power supply, our K-2 drew 1.6 amps with 5 watts of RF output and 2.1 amps with 10 watts of RF output. Both tests were performed on 14 MHz.
Spectral Purity
FCC regulations require the spurious emissions from a 10 watt radio to be at least 40 dB below the carrier, and the K-2 easily exceeded that requirement on all bands.
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 are the links to the spectral purity graphs for our sample: 3.5, 7.0, 10.1, 14.0, 18.07, 21.0, 24.9, and 28.0 MHz.
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
Spurious signals
There were only three "in-band" birdies in our sample, and two of them were of little consequence, because they were at the extreme edge of their bands. The three birdies were located at 3.591, 4.000 and 7.000 MHz. Given the amount of atmospheric noise at these frequencies, only the birdie at 4.000 MHz is likely to be audible when an antenna is connect to the radio.
Power Requirements on Receive
The K-2s firmware allows the user to make a number of modifications to conserve power (for example, the display backlight can be turned off, the meter can be disabled, and so on). When our K-2 was running in its most power consuming mode, it drew 207 ma on receive. When we took all the power conserving steps, the power consumption on receive dropped to 175 ma.
Receiver Tests—When One External Signal is Present
Minimum Discernible Signal
On 14 MHz we measured an MDS of -131 with the preamp off, and -135 with the preamp on. We used the nominal 700 Hz IF filter. Follow this link for comparisons with the MDS of other HF radios.
Phase Noise
We consider this to be one of our most important tests. We measured a carrier to noise ratio of 125 dBc/Hz for our K-2 (14 MHz). Our test frequency was separated 10 kHz from the carrier. Please follow this link for comparisons with the phase noise of other HF radios.
IF Rejection
The K-2 had outstanding results with IF rejection. We measured IF rejection of 136 dB without the preamp, and 147 dB with the preamp. Please follow this link for comparisons with the IF rejection of other HF radios.
Image Rejection
Our sample had an image rejection of 77 dB without the preamp and 76 dB with the preamp. Please follow this link for comparisons with the image rejection of other HF radios.
Audio Output
At a room-filling volume, we measured power output of 1.1 watts into 4 ohms, and total harmonic distortion of 2 percent. .
Receiver Tests—When Multiple Signals are Present
Selectivity
In this report we've introduced a new analytical tool—a computer-based AF spectrum analyzer, named SpectraPLUS . We have used SpectraPLUS and a calibrated noise source to examine the K-2's IF and AF response at four different filter settings. Don't miss this interesting material!
Blocking Dynamic Range
We were unable to measure blocking dynamic range for the K-2, because the test was noise limited (noise from reciprocal mixing dominated our measurement). For MDS test results for other HF radios, several of which were also noise limited, please follow this link.
Third Order IMD Dynamic Range
In one of the more important tests of our review, the K-2 had impressive results. We measured a third order IMD dynamic range for the K-2 of 96 dB with the preamp off, and 95 dB with the preamp on (14 MHz). Please follow this link for comparisons with the third order IMD dynamic range of other HF radios.
Third Order IMD Intercept Point
We calculated third order intercept points for our K-2 of 13 with the preamp off and 7.5 with the preamp on (14 MHz). 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. We measured an excellent second order IMD dynamic range of 99 dB with the preamp off and 101 dB with the preamp on (14 Mhz). Here is the link for comparisons with the second order IMD dynamic range of other HF radios.
Second Order IMD Intercept Point
We calculated second order IMD intercept points for the K-2 of 67 dBm with the preamp off and 67 dBm with the preamp on. Please follow this link for comparisons with the second order IMD intercept points of several 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. The K-2 met the prevailing criterion for "good behavior" in this department, with IMD products about 33 dB below the test tones. Here is the link to an AF spectrum analyzer graph.
Conclusion
Please give us your comments on this review and pass along your own experiences with the K-2. We'd like to publish your thoughts in our monthly column "Readers Write."
For the future, we'd like to develop the equipment and procedures for testing keying and AGC. We're also like to invent some kind of index that correlates weight, power consumption, and performance. Never a dull moment!
We close with a thank you to the ARRL lab. The ARRL has produced a wealth of incredibly valuable testing procedures and information . We're about to wear out our copy of the ARRL Lab Manual. We owe them a huge debt.
Here are some important links:
The lab's goals and equipment.