Author: Al Williams

4460 Articles

Beat Your Coat Hangers Into Antennas, Not Plowshares

April 28, 2020 by 37 Comments

If you are looking for a fun project while you are cooped up and you have some spare coathangers, why not try this 4-element Yagi antenna (PDF)? [Pete N8PR] showed it off at his local ham radio club and it looked like something good for a lazy afternoon. If you aren’t a ham, you could adjust it all for a different VHF or UHF frequency.

For the boom, [Pete] mentions you can use wood, but it isn’t weather resistant. He chose half-inch PVC pipe. He also offers you a choice of material for the elements: #8 wire, welding rod, or — our favorite — coat hangers.

This is a big upgrade from a simple dipole or a vertical made from coax. The yagi should have about 8 dBi gain in the direction it is pointing. The center of the boom doesn’t have any elements, so that simplifies mounting. The insulating boom also makes mounting the driven element a breeze.

If you use the coat hangers, we’ve heard an easy way to get them very straight is to put one end on a vise and the other end in a drill chuck (see the video below). The method will weaken the wire, but the elements won’t have much stress. If it worries you, just go slow on the drill and you might consider annealing the wire with a torch afterward.

It would be easy to make this portable like some other designs we’ve seen. If you want the history and theory behind the venerable yagi antenna, you’ll want to revisit this post.

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Odd Crosley Radios From The 1920s

April 24, 2020 by 37 Comments

You may sometimes see the Crosley name today on cheap record players, but from what we can tell that company isn’t connected with the Crosley Radio company that was a powerhouse in the field from 1921 to 1956. [Uniservo] looks at two of the very early entries from Crosley: the model VIII and the XJ. You can see the video of both radios, below.

The company started by making car parts but grew rapidly and entered the radio business very successfully in 1921. We can only imagine what a non-technical person thought of these radios with all the knobs and switches, for some it must have been very intimidating.

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A CR2032 Battery Eliminator

April 24, 2020 by 26 Comments

Back when batteries were expensive and low-capacity, it was common to buy a “battery eliminator” that could substitute for common battery configurations. [David Watts] must remember those, because he decided to make an eliminator for all the CR2032 battery-driven gear he has. He got some brass blanks about the size of the battery, and you can see the results on the video below.

His first attempt seemed to work fairly well, a sandwich of two brass disks, each with a Velcro spacer and wires soldered on to connect to a power supply. The fake battery looks as though it might be a little thick, but it did work once the battery holder was persuaded to accept it.

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Debugging For Sed — No Kidding

April 24, 2020 by 13 Comments

If you do much Linux shell scripting, you’ve probably encountered sed — the stream editor — in an example. Maybe you’ve even used it yourself. If all you want to do is substitute text, it is easy and efficient. But if you try to do really elaborate editing, it is often difficult to get things right. The syntax is cryptic and the documentation is lacking. But thanks to [SoptikHa2] you can now debug sed scripts with a text-based GUI debugger. Seriously.

According to the author, the program has several notable features:

  • Preview variable values, both of them!
  • See how will a substitute command affect pattern space before it runs
  • Step through sed script – both forward and backward!
  • Place breakpoints and examine program state
  • Hot reload and see what changes as you edit source code
  • Its name is a palindrome

There’s only one word for that last feature: wow.

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Freeze Laser Beams — Sort Of

April 23, 2020 by 5 Comments

They say a picture is worth a thousand words, and by that logic a video must be worth millions. However, from nearly the dawn of photography around 1840, photographers have made fake photographs.  In modern times, Photoshop and Deepfake make you mistrust images and videos. [Action Lab] has a great camera trick in which it looks like he can control the speed of light. You can see the video below.

You probably can guess that he can’t really do it. But he has videos where a real laser beam appears to slowly move across the screen like a laser blaster shot in a movie. You might think you only need to slow down the video speed, but light is really fast, so you probably can’t practically pull that stunt.

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The Back And Forth Of Windshield Wipers And Patent Lawsuits

April 23, 2020 by 50 Comments

Who among us hasn’t dreamed of having some brainstorm idea, prototyping it, and then have some huge company put it into worldwide production? The problem is, that’s not really as easy as it sounds in most cases. Take the case of Robert Kearns. Never heard of him? You use the result of one of his patents pretty often; Kearns invented the intermittent windshield wiper.

If he had sold the patent to one of the big carmakers, this would be a short article. Not that he didn’t try. But it didn’t go very well and while, in the end, he prevailed, it was a very expensive victory.

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Program Guesses Your Regular Expression

April 22, 2020 by 12 Comments

We aren’t sure how we feel about [pemistahl’s] grex program. On the one hand, we applaud a program that can take some input samples and produce a regular expression. On the other hand, it might be just as hard to gather example data that produces the correct regular expression. Still, it is an interesting piece of code.

Even the author suggests not to use this as an excuse to not learn regular expressions, since you’ll need to check the program’s output. It is certain that the results will match your test cases, but it isn’t certain that it won’t accept things you didn’t expect. Bad regular expressions have been the source of some deeply buried bugs.

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