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 Previous: FCC Begins "Software Defined Radio" Inquiry |  Next: In Brief |
By Warren Tobin, W0WT
March 22, 2000
A regen receiver in a world of superhets and DSP? No, you're not in a time warp. Ten-Tec has kitted up a very economical (under $60) shortwave receiver that makes a great first kit or a club or classroom project for newcomers--or just for your own enjoyment. It's also a good kit for those who suffer from "kitbuilder's anxiety syndrome." W0WT shares his experiences.
Let me start with a confession: I enjoy listening to the "shortwave" bands, but I've never owned a general-coverage receiver. I've considered buying a used older model, but that's as far as I've gotten. But, I have an interest in building electronic devices. A product review in QST describing the Ten-Tec T-Kit Model 1340 Transceiver Kit (see "Ten-Tec T-Kit Model 1340 Transceiver Kit," QST, Sep 1998) provided the motivation to do some research into kit building.
My experience in constructing kits includes building a Heathkit code oscillator about 12 years ago. Since then I have built a few small kits--those with a single circuit board and fewer than 20 parts.
Through my research, I discovered the Ten-Tec T-Kit Model 1253 Regenerative Shortwave Receiver. "Aha!" I said. "I can kill two birds with one stone. I can satisfy an urge to build and obtain a shortwave receiver for general use."
I purchased a kit from the manufacturer and looked closely at the literature and parts. After that review, I decided that I was up to the challenge and was ready to proceed.
In my review of Ten-Tec's instruction manual and other materials, regenerative receivers (also known as "regens," "gennies," or "rush boxes") were popular in the 1920s and early 1930s but fell out of favor for general use when superheterodyne (superhet) receivers became more widely available. Regenerative receivers were left to tinkerers and beginners.
These simple and sensitive receivers had the disadvantages of instability, "touchiness," lack of selectivity (difficulty in separating strong stations), and a tendency to generate interference to other receivers. On the plus side, regens can be very sensitive.
Ten-Tec carefully evaluated this kit with the goal of providing an inexpensive kit that would be able to be constructed by a beginner--preferably with an Elmer to help. Ten-Tec's engineers researched receiver designs and parts availability. They arrived at a solid design using modern devices. The kit combines the simplicity of yesterday's design with today's technology to provide a low-cost shortwave receiver.
The radio's audio amplifier uses a commonly available car stereo integrated circuit to drive a three-inch internal speaker or the user's external speaker or headphones. The kit uses an electronic bandswitch from a commonly used computer semiconductor. This reduces the parts count and provides an effective method to provide nine shortwave bands.
Frequency stability is provided by a readily available voltage regulator IC.
Finally, the receiver uses molded inductors to reduce the unit's size, to provide for a standard frequency range for each band, and to aid in the ease of construction. This was my first experience using molded inductors. These inductors are about the size of a resistor and are soldered to the board in a similar manner. As I was considering building this kit, I was a little concerned about properly winding inductors and the molded inductors greatly relieved my anxiety.
Getting ready to start the parts inventory. |
As an old elephant joke goes: "How do you eat an elephant?" The answer? "One bite at a time." Using this one-bite-at-a-time process, I approached the construction of the receiver in a methodical step-by-step fashion. I read the manual three times to learn about the project and then inventoried the parts to verify I had received all of them and to become more familiar with them.
Ten-Tec's instruction manual is clear and provides an easily followed checklist. The manual recommends the kit be constructed in phases as described below.
The unit after the audio amplifier test. Clear overlays on the circuit board make installation easy. The toggle switch which was added is on the circuit board near the potentiometer on the far right. |
Phase 1 carefully starts the builder along the path of installing the components in the main circuit board. The checklist carefully describes the differences in Mylar film capacitors, ceramic disc capacitors, resistors, and molded inductors. The checklist also helps the builder select the proper transistors and electrolytic capacitors and to properly orient them on the circuit board. Through describing the components, the proper way to install them and printed overlays on the circuit, the probability of installing an incorrect part or installing a part in an incorrect manner is minimized.
When I had completed all the steps, I felt confident that the audio amplifier would work correctly when I applied power. This was confirmed when I successfully completed the Phase 1 Optional Audio Amplifier Test. These periodic tests help buttress the beginning builder's confidence in his work and also help in the diagnosis of any potential problems by help eliminating the items that do work.
Phases 2 and 3 lead the builder through the addition of most of the parts on the main circuit board. At step 3-33, the builder will need to make a decision about installing optional parts in the regeneration circuit. C43 and L10 are components which were added to the original circuit. These components add to receiver sensitivity, but their inclusion requires somewhat more careful adjustments to regeneration control.
I made my first "modification" to the receiver by adding a single pole toggle switch to C43. I wanted the option of adding the optional circuit without needing to completely disassemble the unit. In addition, by making it switchable, the receiver would provide additional flexibility. I considered mounting the switch on the panel but I didn't believe that I would want to switch this circuit very often.
Phases 2 and 3 went quite quickly for me. Although I was being very careful in assembly, it seemed that in a very short period of time I was ready for Phase 4.
Phase 4, the Basic Receiver Operation Test, provides the opportunity to verify the dc voltage control, detector, tuning, and audio amplifier circuits are working properly. Successfully completing Phase 4 was a real confidence builder. "By golly, it works!" I said to myself as I was preparing for Phase 5.
The bandswitch board's front side during Phase 5 construction. |
The bandswitching control board is a double-sided silver plated circuit board. This was the first time I had soldered on this type of board. I elected to add a 16-pin DIP socket instead of soldering the 16-pin decade counter IC directly to the circuit board.
The bandswitch board's back side after IC installation. The smoothing capacitor will later be installed across the zener diode (lower center). |
I approached this section with slight apprehension. I knew the unit worked on 40/41 Meters, but if I had made a mistake, I would have to diagnose and possibly disassemble the radio to correct my errors. I double-checked every item on the checklist and slowly assembled the unit. The only difficulty I had was installing the battery shelf, because the smoothing capacitor--added in Phase 6--stuck out far enough to be caught by the battery case. I'd recommend that Ten-Tec advise the builder to avoid hitting the capacitor with the battery case during installation.
I purchased the power supply as listed in the manual (Radio Shack 273-1652) to provide 12 V dc. Using this device, I could hear AC hum in the speaker. The solution is to use shielded (coaxial) cable from the antenna to the receiver. Initially, I just used 10 feet of hook-up wire to test the receiver.
This unit is really "hands on." I started by not employing the optional C43/L10 add-on previously discussed. In my first hour or two of casually listening, using only the 10 feet of hook-up wire--and after some practice with the regeneration control--I was able to copy international broadcasts on several bands, W1AW code practice on 20 meters and some hams ragchewing on 40-meter SSB. In addition, I copied some RTTY and other digital signals on 40.
It really works, and I'm getting more expert every day with using the regen control.
The completed Ten-Tec Model 1253. [All photos by the author] |
In the manual, Ten-Tec says:
Our goal was to design the very best multi-band shortwave radio kit for AM-SSB-CW reception in its price class. We live now in an age where that kind of money can buy very sophisticated major-brand electronics gadgets, including stereos, cordless phones, music keyboards and even portable shortwave radios (without CW-SSB reception capability).
Based on my experience, I think Ten-Tec met its goal. I enjoyed building and using the unit. I fire it up a few times a month to listen to shortwave broadcasts from overseas.
The price of this little kit--$59 plus shipping and handling--may be among its best features too. Also, for those interested in this kit for possible use in electronics classes or as a ham club project, the manual provides additional information for classroom use. By the way, another product that might be of interest to teachers and clubs is the T-kit Model 1054, priced at under $20 and an economical and simplified version of the same regen circuit. The 1054 kit has mechanical bandswitching for four bands between 5 and 15 MHz.
Ten-Tec's information line is 423-453-7172. The toll-free order line is 800-833-7373.
Editor's note: Warren Tobin, W0WT, lives in Jamestown, North Dakota, and is employed by Stutsman County. Warren has a wide variety of interests. When time permits, he enjoys making CW contacts on the high frequency bands. He wrote an article for club news in the November 1988 edition of QST (p 78). He says he hopes his article will encourage others to try kit building or homebrewing. He's following up his successful experience with this kit by working on a kit 30-meter transceiver and a Tuna Tin II transmitter. He's also homebrewing an interface for PSK31. "So many projects so little time!" he says.
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