The ARS QRP Lab Reviews the NorCal 20 Transceiver
The ARS Sojourner
Like many club projects, the NorCal 20 promptly became the subject of a series of published "mods." Probably the most important of these relates to the radio's AGC system. The mods have been collected in the Red Hot Radio site (see below); you can also find many of them in the Spring, 1999 issue of QRPp.
We started our testing with a single sample of the NorCal 20. After that radio failed to meet our expectations, we became concerned that our sample might have one-of-a-kind deficiencies. So we asked another member of ARS to lend us a second sample (which had slightly worse test results than the first sample).
Our first sample had no mods. The second sample had received the AGC and 10 turn pot mods. When our report refers to "our sample," we mean the first sample. When appropriate, we occasionally also refer to test results for the second sample.
The NorCal 20 is no longer in production. However, a successor transceiver, the Red Hot NorCal 20, is being produced by Red Hot Radio. A full description of that radio can be found on their web site at http://www.redhotradio.com. Please keep in mind that this review applies only to the original NorCal 20. We have not tested the Red Hot Radio version.
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Transmitter Tests
Power Output
Rated output for the NorCal 20 is 0 to 5 watts nominal, 7 watts typical. Our sample produced a maximum output of 5.5 watts with a 13.8 volt power supply and 4.2 watts with a 12 volt power supply.
Power Requirements on Transmit
With a 13.8 volt power supply, our NorCal 20 drew 1.15 A with 5.5 watts of RF output. With a 12 volt power supply, our NorCal 20 drew 970 mA with 4.2 watts of RF output.
Spectral Purity
FCC regulations require the spurious emissions from a 5 watt radio to be at least 40 dB below the carrier. Our sample 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. In the charts for the NorCal 20, you will notice that the chart includes identical bars for "with preamp" and "without preamp." In reality, the NorCal 20's preamp cannot be turned off.
Receiver Tests—When No External Signals are Present
Tuning Range
Our first sample had the standard 1 turn pot, and had a tuning range of 14.040 to 14.075 MHz. The manual specifies a nominal tuning range of 30 kHz.
Our second sample had the 10 turn pot mod, and had a tuning range of 14.004 to 14.071 MHz. The manual specifies a nominal tuning range of 70 kHz.
Stability
The NorCal 20 uses a varactor-tuned VFO, so a certain amount of drift is to be expected. The specifications call for approximately 300 Hz of drift during the first 30 minutes, and 50 Hz of drift per hour thereafter. Our sample first drifted up in frequency, and then down. Overall, you could say that its stability fell within the specifications.
Please follow this link to a graph of the radio's stability during the first 45 minutes of warm up.
Spurious signals
There were no birdies in our sample.
Power Requirements on Receive
Our sample drew 145 mA on receive with a 13.8 volt power supply, and 130 mA amount with a 12 volt power supply. Both were less than the specified nominal receive current of 150 mA.
Receiver Tests—When One External Signal is Present
Minimum Discernible Signal
On 14 MHz we measured an MDS of -129 dBm, in a 6 dB bandwidth of 330 Hz. This is significantly less than the specified nominal sensitivity of -135 dBm. Our second sample had a measured MDS of -127 dBm. (We gave the NorCal the benefit of the doubt and used -129 dBm for the remainder of our tests.) We confirmed our MDS measurements by measuring the noise figure, using a calibrated noise source.
Please follow this link for comparisons with the MDS of other HF radios.
Phase Noise
The NorCal 20 had very good performance with its phase noise. We measured phase noise of -136 dBc/Hz.
Please follow this link for comparisons with the phase noise of other HF radios.
IF Rejection
Our sample had IF rejection of 80 dB. Please follow this link for comparisons with the IF rejection of other HF radios.
Image Rejection
Our sample had an image rejection of 95 dB. Please follow this link for comparisons with the image rejection of other HF radios.
Audio Output
With the volume knob at three quarters of its full position, our NorCal 20 produced 860 mW into an 8 ohm load. Total harmonic distortion was 15 percent.
Receiver Tests—When Multiple Signals are Present
Selectivity
We measured a 6 dB IF and AF response of 330 Hz, as compared to the nominal bandwidth of 300 Hz. You will find interesting information about the width and shape of the NorCal 20's IF and RF response in this AF spectrum analyzer graph.
Blocking Dynamic Range
Our NorCal 20 had a blocking dynamic range of 118 dB. Please follow this link for comparisons with the blocking dynamic range of other HF radios.
Third Order IMD Dynamic Range
This is one of the most important tests in our review. Unfortunately, the NorCal 20's third order IMD dynamic range was only 84 dB, considerably below our expectations. 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 third order intercept point for our NorCal 20 of -3 dBm. 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 NorCal 20, the test signals generated an anomalous AF spectrum, in which it is not possible to make a meaningful measurements of IMD products. We're not sure whether our test result indicates a potential problem with the radio's audio, or whether the test simply failed for unknown reasons. In any event, we have included a link to the AF spectrum analyzer graph, without further comment.
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 NorCal 20 has some impressive features, including a clean, reasonably stable VFO, built in keyer and audio frequency "read out," good selectivity, and very good second order IMD dynamic range. And we have nothing but admiration for the hard work of all the volunteers who made this complex project happen.
But we were troubled by the outcome of some of our most important tests. We tried to go the extra mile, by getting a second sample, and running the key tests multiple times. Unfortunately the tests kept suggesting the same thing. Somehow, the trade offs that were designed into this radio were not working.
By going to a diode ring double balanced mixer, the designers willingly took the penalty of high current consumption in order to achieve a "crunch proof" front end, with excellent third order IMD dynamic range. But our tests suggest that this goal was not achieved. On top of this problem, our samples were a little hard of hearing. We keep preaching not to make a horse race out of sensitivity, but our samples were among the least sensitive radios we've encountered.
Perhaps there is an easy explanation for all this--we earnestly hope so. Maybe there is some basic characteristic of the radio that threw off the testing. Maybe we made a bonehead mistake. Or, if the radio is in fact flawed, perhaps there is a simple fix.
We conclude with an open invitation to all who contributed to this project to help us out of our dilemma. Please send us your comments. We will gladly update this report to reflect any new information we may receive.
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