"RIG HERE IS HOME BREWED"
SOME THOUGHTS ON BUILDING A TRANSMITTER
BY BILL, N2CQR/HI8
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My introduction to ham radio came via the nightly AM radio programs of that master story-teller Jean Sheperd (K2ORS). My dad and I would sit in the kitchen and tune to New York's WOR - 710 AM and listen to "Shep's" tales from days- gone-bye. Amidst the stories about his senior prom and catastrophic Fourth of July parties, Shep would from time to time talk about ham radio. Because of these programs, my first images of the hobby involved enthusiastic youngsters scouring parts shops in search of exotic components for use in the construction of mysterious short wave radios.
With encouragement and help from Mom, Dad and the Crystal Radio Club (W2DMC) I soon became a licensed ham and got on the air. I suppose it can be said that I did some home brewing - I built the power supply for a Heath monoband SSB rig from components salvaged from a T.V. set, but I never quite felt that I'd shared in the radio-building adventures of Jean Shepherd and his intrepid friends. I wanted to be one of those guys! I wanted to build my own radio! As a teenage ham I made a couple of attempts to join the "home-brew club," but I was denied this exalted status because of poor metal working skills (you had to be good with a chassis punch in those days) or because I bit off more than I could chew and tried to build things beyond my capabilities.
When I returned to the airwaves two years ago, I found that my long dormant yearning to "home brew" returned with a vengeance! This time I decided to play it smart: I would start out slow with easy projects that seemed sure to work. I would look for circuits that I found easy to understand and I would avoid anything that seemed to require skills or tools beyond my reach. I set as my goal the eventual construction of a transmitter that I could incorporate as part of my station - a transmitter that would enable me to say, "RIG HR IS HB!"
While there is a lot of debate about the place of Morse Code in the modern era, CW does offer one undeniable advantage: extreme simplicity. For the beginning homebrewer, a Morse Code transmitter offers the easiest avenue to success: Rigs just don't get any simpler! I was shooting for success via simplicity so - for me CW - was clearly the way to go.
The QRP movement provided lots of schematics for easy-to-build rigs. I started out with a single transistor transmitter called the Michigan Mighty Mite (featured in the March 1992 issue of CQ). This rig is simplicity itself - the coil is wound on a discarded plastic film container. I put it together on a little piece of perf board. At first it didn't seem to work but with my receiver tuned to the crystal frequency, I fidgeted with the components a bit until - Eureka! - it started to oscillate! I was generating RF! I felt like I was right up there with Maxwell, Hertz and Marconi! I wasn't able to make any contacts with this little rig, but my confidence level soared and I began to search for a more substantial transmitter project.
I found just what I was looking for in the ARRL publication "QRP Classics." The 6 watt variable crystal oscillator (VXO) controlled CW transmitter circuit caught my eye because the circuit seemed to come right out of a basic radio theory textbook: there it was, oscillator, buffer, driver and power amplifiers - all discrete transistors, no mysterious "black box" IC's, no exotic experimental circuitry... Here was a circuit that I could understand! I was also attracted by the five or six watts of power out promised by the circuit - this seemed to be enough to guarantee some QSO's. The variable crystal oscillator seemed to provide the simplicity and stability of crystal control without all of the inconvenience of being "rock bound" on one frequency. The printed circuit board layout was very simple, with the components sufficiently spread out to allow for easy assembly. I decided to build the twenty meter version of this transmitter.
From the electronic parts catalogs that had been accumulating in my shack I began to order the components. I supplemented this mail order effort with visits to Santo Domingo's second hand parts stores. It was fun to plunge into the chaos of those stores and emerge with tiny components that would soon find there way into my transmitter!
On this little rig, the two most difficult tasks in the construction were the printed circuit (PC) board fabrication and the winding of the coils. While there might be a temptation to try and acquire a ready made printed circuit board, if you are shooting for that warm glow of satisfaction that comes from having built it "all by myself," I suggest that you make your own board. (Would that be a Politically Correct PC board?). This is not as difficult as it might first seem - there is a lot of literature out there on how to make your own boards and there are many tools and kits available. Leave yourself some margin for error and be prepared to discard one or two of your first attempts. There are a lot of different ways to lay out the circuit pattern and to etch, clean and drill the holes in the board. As I went through the process I sort of developed my own favored technique. I wasn't quite happy with the first board I produced, so I made a second board that came out a lot better. The first board - while kind of ugly - later served as the base for a thirty meter version of the same transmitter.
Winding the Toroidal Coils seemed tricky at first but after consulting the literature for some guidance, I sat down with the cores and the wires and started winding! After a while it became kind of relaxing! I wound all the coils in one afternoon and added them to my now growing collection of components. Having had a couple of bad experiences with electronic projects that didn't work, I decided to proceed carefully in the hope of avoiding the agony of troubleshooting. I checked all the components with my volt-ohm meter before mounting them on the board. With a large wad of steel wool at hand, I made sure that the board surface and the component leads were clean and shiny before soldering. After soldering each joint, I made a continuity check with the VOM to make sure I hadn't created a cold solder joint.
The board filled with components very quickly and soon I was approaching the moment of truth! I didn't even wait to mount the PC board in a cabinet. With nervous fingers and with my receiver tuned optimistically to the transmitter's crystal frequency, I connected my key, dummy load and finally the battery to the spider-like creation that had taken so long to assemble. When I finally connected the red wire to the positive battery terminal, I was rewarded with a solid tone from the receiver. The joy of oscillation! I knew that at least one stage of the rig was working right off the bat.
A few quick checks showed that the amplifiers were amplifying - I was now ready to challenge the ionosphere with 5 watts of continuous wave RF! I know that when most articles of this genre get to this point a fantastic claim is often made: "I then connected the milliwatt transmitter to a garbage can in my basement and worked Antarctica through the pile up on the very first call!" Well my homebrew success story is not quite so dramatic (or fantastic) but I did manage to work Poland on the first call from this little rig. It was quite satisfying to look at that little collection of parts, wire and solder and think that I had used it to bridge the mighty Atlantic.
After working Europe on the first try, I decided that this little rig definitely warranted a proper cabinet so I soon had it mounted in a little metal and plastic box that I'd acquired by mail order. Now it looked like real radio. After a while I got tired of having to open up the cabinet to change the crystal, so I "designed" a little rotary switch arrangement that let me change crystals with the turn of a switch. I find this kind of little modification is very rewarding - the homebrewer has the opportunity to use his or her ingenuity in making improvements on a radio.
This little construction project was a big success for me. By the
I was finished I had some very useful and reliable new equipment to add
to my station. The 30 meter version of the gave me my introduction to
WARC bands. As luck would have it, shortly after completing the twenty
meter rig, my main transmitter (an old but much loved HT-37) developed
serious problems that put it off the air for a couple of months.
with my homebrew transmitter and a Drake 2-B receiver I was able to
on the air. Most important of course was the satisfaction that came
using a transmitter that I'd built with my own hands - I felt that I
earned a place among those intrepid lads who had stalked the parts
canabalized old radios, filled their basements with solder smoke and
on the air with homebrew gear! "RIG HR IS HB!" FB!
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