H. P. Friedrichs (AC7ZL) Homepage
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Radio Project Articles
Check out the dummy antenna I built from scraps. It should be good for about 200 watts!
In the old days, wireless experimenters would wind their coils on Quaker Oats (tm) or Morton Salt (tm) boxes. Follow this link to see the construction of a nifty radio built from more contemporary trash.
If you build the CDROM radio, you're going to need some kind of earphone to go with it. Why not make one? Here's how.
The BC-348 was a standard-issue receiver on some the most famous bombers in history, including the B-17, the B-24, and the B-29. A chance encounter at a hamfest left one of these treasures in my hands, but could I get it working?
A military VHF radio travels from France to the deserts of Iraq, through combat, and now to my benchtop. If only rigs could talk!
Once I got my TR-VP-13 cabled up and working, I needed a source of power, both for base and mobile operation. I could have slopped something together, but I decided to build something more aesthetic and more elaborate. I used this as an opportunity to explore and express a number ideas related to rugged equipment housings, chassis fabrication, and lead-acid battery packs. Even if you don't have a TR-VP-13, you will find this article interesting.
What do you get when you cross a 1920's era circuit with a 1970's era sitcom and a box full of junk? Fictional character Fred G. Sanford might have answered this way, "A radio, you big dummy!"
Perfect for crystal radio or simple tube receivers, they're sensitive, they sound good, they're easy to build, and they're dirt cheap. What more could you want?
If you have a basic understanding of how electronic parts work, you can probably assemble a handful of them into something useful. But, if you understand the physical principles underlying the design of those parts, it's sometimes possible to apply them in ways far beyond their intended purpose. In this article, I describe a "hack" where a common display device is used as an electronic amplifier... and a pretty good one at that.
Cell phones are great... when they work. Unfortunately, there are a lot of circumstances and a lot of places when and where they won't, and this always seems to happen when you need them the most. Amateur radio operators understand this, but because cell phones are so common, even we can become complacent. A recent adventure in an Arizona desert inspired me to purchase an HT (handy talkie) and to fashion a set of accessories that will assure my ability to communicate in the future, whether my cell phone works or not.
Question: What do you get when you combine an army tent in a middle-east desert with wind, blowing sand, and an antenna? If you answered "high voltage electricity," you're right! Now, how do we get rid of it?
Kitchen and garden-shed chemicals can be applied to copper to produce semiconducting junctions. Add a piece of plastic, a bit of metalwork and a handful of bolts, nuts, and washers, and you can fabricate an interesting, attractive, and functional piece of primitive radio equipment.
A simple radio circuit with a single vacuum tube is enough to give a clever builder access to broadcasts from around the world. This article describes an attractive little vacuum tube radio receiver, built from a handful of salvaged parts that had been accumulating in my junk box.
If you're less than 50 years of age, and you don't tinker with vintage radios or antique test equipment, you're probably unfamiliar with the magic-eye tube. Pity, because you've missed out on seeing one of the neatest display devices ever produced. This article describes an approach to building a fairly convincing electromechanical equivalent, using simple junk parts.
Every crystal radio set builder knows that you can detect radio signals with a tiny glass germanium diode. If you want to go old-school, you use a chunk of galena and a wire catswhisker. But are those your only options? You might be surprised to learn that oldtimers knew of many dozens (perhaps hundreds) of useful minerals, metals, and compounds that can be combined to fabricate primitive semiconductor diodes. Read about it here.
Amateur radio operators have a long and rich tradition of building their own tools and equipment from scrapped, salvaged, and repurposed junk. Morse keys are no exception. For years, hams have fashioned creative and functional sending instruments from a staggering variety of household odds and ends. Here is a novel design for an exceptionally nice straight key which is fashioned from a disemboweled computer hard drive. Why not build one of your own?
Who would have thought that the black particles found in the sand of Arizona roads and washes would find application in a radio tuner, oscillator, antenna, or transformer? Well... I did... I tried it... and it works! In fact, you may be surprised as to how far I actually went with this idea. Read about my experiments here.