The ARS QRP Lab Reviews the MFJ Cub Transceiver
The ARS Sojourner
This is an interesting review. Our first sample radio (a 15 meter version) was kindly lent to us by Larry East, W1HUE. Larry's Cub has been extensively modified. Those modifications have been published on the Internet, and in the July, 2000 issue of The QRP Quarterly. (See the excellent material on QRP-ARCI's site. http://www.qrparci.org/)
Originally, we had thought that the modifications would not impact our review. However, we later discovered that one of the mods had adversely affected the sensitivity of our sample. So we tested a "stock" version of the 15 meter Cub and made appropriate corrections to our data and graphics.
A reasonably complete set of specifications for the Cub appears on MFJ's web site, and we won't repeat them here. http://www.mfjenterprises.com/index.htm
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Transmitter Tests
Power Output
Rated output for the 15 meter Cub is 1.0 watts. Our sample produced a maximum output of 1.1 watts with a 13.8 volt power supply and 1.0 watts with a 12 volt power supply.
Power Requirements on Transmit
With a 13.8 volt power supply, our Cub drew 255 mA with 1.1 watts of RF output. With a 12 volt power supply, our Cub drew 255 mA with 1.0 watts of RF output.
Spectral Purity
FCC regulations require the spurious emissions from a 1 watt radio to be at least 30 dB below the carrier. In our sample, the second harmonic was 38 dB below the carrier, and it therefore met the FCC's requirement. MFJ's specifications state that spurious emissions will be 40 dB below the carrier.
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
The tuning range for our sample was 21.020 to 21.062 MHz.
Spurious signals
There were no birdies in our sample.
Power Requirements on Receive
Our sample drew 39 mA on receive with a 13.8 volt power supply, and 37 mA with a 12 volt power supply. MFJ specifies 36 mA on any 12 to 15 volt power supply.
Receiver Tests—When One External Signal is Present
Minimum Discernible Signal
On 21 MHz we measured an MDS of -133 dBm.
Please follow this link for comparisons with the MDS of other HF radios.
Phase Noise
We measured phase noise of -124 dBc/Hz at a spacing of 10 kHz from the carrier.
Please follow this link for comparisons with the phase noise of other HF radios.
IF Rejection
Our sample's IF rejection was 78 dB, which is about the same as other similar radios. Please follow this link for comparisons with the IF rejection of other HF radios.
Image Rejection
Our sample showed a middle-of-the-road image rejection of 65 dB. Please follow this link for comparisons with the image rejection of other HF radios.
Audio Output
Our Cub had very good audio performance. At full volume, total harmonic distortion was only 1.0 percent.
Receiver Tests—When Multiple Signals are Present
Selectivity
We measured a 6 dB IF and AF response of 740 Hz, as compared to the nominal bandwidth of 750 Hz. You will find interesting information about the width and shape of the Cub's IF and RF response in this AF spectrum analyzer graph. In comparison to other similar radios, the Cub's shape factor was not impressive.
Blocking Dynamic Range
Our Cub had a blocking dynamic range of 106 dB, which was about average for radios of a similar kind. Please follow this link for comparisons with the blocking dynamic range of other HF radios.
Third Order IMD Dynamic Range
The Cub's third order dynamic range of 81 dB was in the middle of the range for similar radios. 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 Cub of -11.5 dBm, which was typical of other similar radios. Please follow this link for comparisons with the third order intercept points of other HF radios.
Second Order IMD Dynamic Range
Our sample had a respectable second order dynamic range of 95 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 57 dBm, putting the Cub in the middle of the pack. Please follow this link for comparisons with the second order IMD intercept points of other HF radios.
In-band IMD
The Cub's in-band IMD performance was excellent, which is another hint that the Cub's audio circuitry performs very well.
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 MFJ Cub has turned out to be a "happening," as well as a radio. QRP-ARCI has organized a group purchasing program for the Cub, and in turn the Cub has been the focal point for an outstanding educational program.
The Cub is easy to build. This feature, and the QRP-ARCI's support, have probably attracted a number of newcomers to the QRP community. We vigorously support anything that draws new participation into this magic hobby of ours.
On the other hand, experienced low power operators might have some reservations about the Cub. In terms of its topology, it might be described as a "me too" radio. Designs based on the NE602 (and its successors) and the LM386 have been around for a long time. The Cub has a herd of competitors with similar topologies (from such companies as Wilderness Radio and Small Wonders Labs).
Keep in mind that our sample Cub was the 15 meter version. It is possible that the models for different bands would have performed differently.
We are always interested in your own opinions. If you want them to be published, we will be happy to include them in our column "Readers Write." Use our automated comment page to get in touch with us.
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