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 Previous: Montana High Schoolers Pose Tough Questions via Ham Radio | ![Next (later) Story](/images/sty-up.gif "ARRL Announces "Big Project" Logo Winner, Unveils New Design"){kind=small} Next: ARRL Announces "Big Project" Logo Winner, Unveils New Design |
By Paul Huff, N8XMS
February 4, 2002
To create is a universal human trait. For a ham, this urge manifests itself in a desire to build equipment, circuits, antennas--anything related to Amateur Radio. N8XSM discovers that even a state-of-the-art radio kit still requires familiar, time-tested assembly methods for completion.
My First Kit
For several months my wife Susan and I had been planning a trip to the Smoky Mountains of Tennessee. We would stay at a Bed and Breakfast called The Little Greenbriar Lodge. Since the lodge was about a 30 minute drive from Ten-Tec headquarters in Sevierville. I expressed an interest in trying to fit a visit to the plant into our vacation time. Although Sue is not a ham she has always been interested in my hobby and has supported my radio interests, so she readily agreed.
Our tour of the plant was very interesting and far more extensive than I had expected. After the tour I had an opportunity to make a couple of quick QSOs on an OMNI VI Plus that is available for visitor use. Sue then suggested that I pick up a souvenir of our visit. But since the $2,585 price tag on the OMNI was a bit high for our budget, I looked around for something a little more reasonable. Ten-Tec's series of CW QRP rigs, at $95 plus tax, looked interesting but I was a bit apprehensive about being able to successfully complete the project. The salesman told me that although the rigs have some fairly sophisticated circuitry and features, they could be successfully built with a minimum of test equipment and electronics savvy. Since I had been interested for a long time in trying out a QRP kit, I decided to take the plunge and purchase a 20 meter version.
My kit building experience is extremely limited and certainly justified my apprehensions. Many years ago I assembled a Heathkit Novice transmitter, but that was before the days of solid-state components and etched circuit boards. More recently I successfully built a keyer from a kit of about a dozen components, and also fabricated a very simple rig/computer PSK31 interface consisting of about three parts and a few connectors. This limited experience really meant, at the most, that I knew how to solder. My workbench was even sparser than my experience and consisted of a table in the basement family room, basic hand tools, and an old analog VOM.
Assembly Begins
 Assembly begins. "First, check the parts and read the instructions," says Paul. |
The Ten-Tec box contained a 76 page assembly manual, a nice case for the finished rig, assorted connectors and hardware, a 3.5 x 5 inch etched and silk-screened circuit board and a number of plastic bags containing almost 240 components that would eventually be installed on the board. It was impressive. I found that my 46-year-old near-sighted vision needed some help reading the labels on the circuit board and the markings on the parts. A magnifying glass solved that problem.
Setting all the cool toys (parts) aside, I took a careful look at the assembly manual. The first 28 pages contained general information about QRP operation, various rig specifications and parts lists. Especially useful were a block diagram of the transceiver and a brief explanation of what each section did. A careful reading of this information was not only helpful for kit assembly, but was also a very good general education on basic transceiver design. Assembly is divided into eight phases. For each phase, the manual provides an enlarged parts placement diagram and step-by-step assembly instructions with convenient check-off boxes. Each phase also includes progress tests that must be performed to check the correct functioning of that part of the circuit.
Working under the philosophy that haste makes waste, I took about three hours to complete the keying and dc-input circuitry of phase one. The progress test consisted of checking a few voltages as I keyed the rig by touching two wires together. My work passed the test with flying colors and I was thrilled. I knew that it was probably the easiest phase of construction, but I was off to a great start.
Problems Develop
 Testing the VFO output. Note the ample construction manual. |
Phase two consisted of building the very critical transceiver VFO. It took me about four hours to complete the basic work. The main frequency-determining component in the circuit was a toroid inductor that was specified as 17 turns of #28 wire on a T-44 core. For toroids, each pass of a wire through the core constitutes a turn. Unfortunately I was confused on this point. The assembly-manual drawing showed only 16 such turns. I decided to go with the 17-turn printed instructions. The winding process itself was a lot like sewing a button--something that my mother had taught me when I was just a little kid.
The test for this phase consisted of finding the VFO's signal--somewhere between 7.9 and 8.2 MHz--with a frequency counter or calibrated receiver. Since I didn't have a frequency counter, I pressed my main station rig into service. After a while I found what I thought was the VFO output at about 7.5 MHz. This was much lower than specified so I reasoned that my original interpretation of toroid turns must have been wrong. I unsoldered the coil, removed a turn, and re-soldered it onto the board. After another three hours of tweaking the turns I got the VFO output into an acceptable range and moved on to phase three. Phase three consisted of building a mixer and filter that are supposed to change the VFO's output into a 14 MHz signal. The assembly was straightforward but when I went to test the results I couldn't find the 14 MHz output. I called the technical support line at Ten-Tec and they told me that my problem was almost certainly that toroid inductor back in the VFO section of the rig. This was not exactly encouraging news since I'd already spent more than three hours messing around with that one little coil.
I needed a break, so I decompressed for a couple of days on other activities. As a math teacher I have observed that one of the most interesting features of the human mind is its ability to continue to work on a difficult problem at a subconscious level. This is what must have happened for me because after a couple of days of not consciously thinking about it, I had an idea. I had noticed during my initial phase two testing that, without changing the VFO tuning, I could hear weak output at more than one frequency. I also knew that there is no such thing as a perfect VFO output and that the purpose of filtering in the mixer stage is to suppress frequency spurs. Was it possible that I had tried to align my VFO on one of these spurs?
Careful tuning of my station rig finally revealed an S9+60 dB mixer output at 9.0 MHz. I unsoldered the VFO toroid, rewound it with the original number of turns and soldered it back in. That did it. I now had a nice 14 MHz signal. I was elated.
Construction phases four through six went without any significant hitches although at one point in phase four I used a wrong value resistor. I discovered the mistake when I read the progress-test instruction: "Double-check the installation of each part in the preceding three circuit stages." Wow, Ten-Tec thought of everything. It was especially thrilling to actually hear 20-meter signals on the little rig at the completion of phase six.
Almost Done
 The QRP project is about halfway to completion. |
Final construction phases consisted of a low pass filter (with more toroids), T-R switch circuitry, and final assembly into the cabinet. I was starting to get excited in anticipation of the completion of the project.
|
Lessons Learned
This project
was a lot of fun and was a great learning experience. Even with the repair bill
figured in, it was well worth the cost. In no particular order, here are some
of the important lessons I learned:
|
At first the final alignment seemed to go well, but when I switched over from a dummy load to my actual antenna more problems developed. No matter what I did with my antenna tuner, I could not get the rig to load properly. Apparently there was a significant impedance mismatch and RF was bouncing back into the transceiver. By now it was too late in the evening to call Ten-Tec for help so I wrote a lengthy description of my problem and zapped it to them as an overnight fax from my computer. I was very surprised the next morning when a company technician called on the phone. He told me that the problem was probably in the three toroid coils that make up the final low-pass filter. I checked the turn counts, but nothing I tried made any difference. I decided to send the rig back to the company for repair.
 The completed 20 meter QRP kit sits atop an IC-725 transceiver. Paul's first QRP contact is confirmed by KK6AW's QSL card. |
Success at Last
About two weeks later I received a bill from Ten-Tec for $27.50 plus tax and shipping. The invoice simply stated: "Aligned transmitter stages. Checked receive. All O.K." I phoned in a credit card authorization and a few days later I had my transceiver. I could see that some fine adjustments had been made to the low-pass filter coils, but there had apparently been no major problems with any of my work. I tried to take some comfort in that fact.
I hooked up power, key, and antenna and fired up the rig. The band was rather quiet but it was encouraging to see that the rig loaded up into my antenna without any problem. After about 20 minutes of tuning around the band and trying a few calls I responded to a CQ from KK6AW and he came back to me. Kelsey was located in Auberry, California and he gave me a 449 report. The conditions weren't very good so we didn't hold the contact for long but my first QRP QSO was now in the log and it felt great.
After that first QSO the only work remaining was to calibrate the numbers on the rig's tuning dial. I first made up a little table and wrote down about 10 dial-number/frequency combinations, which I spotted with my regular station transceiver. This would certainly have been enough accuracy for any casual use, but as a mathematician I just had to take it a step further. Since the relationship between dial number and frequency wasn't really linear, I next did some curve-fitting statistical analysis on the numbers and found an equation that gave an almost perfect fit to the data. I used a graphing calculator to do this work but it could also be done with almost any computer spreadsheet program. I then used my new equation to create an accurate calibration table for the rig.
Very casual operating over the next three days produced contacts with six more states and signal reports ranging from 339 to 599. I also worked F5BBD, Daniel, in Boue, France. He gave me a 559 report. I made these contacts with a 4.8 W rig that I had (almost) built myself and a multiband trap-vertical antenna that radiates equally badly in all directions. I was in ham heaven.
Conclusion
I am now completely hooked on QRP and kit building, and I am already making plans for future projects. Why not give it a try yourself?
ARRL member Paul Huff, N8XMS, was first licensed as WN0BJC in high
school in 1970. His grandfather Emory, W0MA (SK), was his Elmer. College,
marriage, and a career as a high school math teacher kept Paul from Amateur
Radio for more than 20 years. He earned his Extra Class license in March 2000.
Paul is almost exclusively an HF CW operator and, since the completion of this
project, has been totally QRP. He lives in Livonia, Michigan with his wife Sue
and two children--Mike and Jenny. The author can be reached at N8XMS@ARRL.net .
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