Just How Good Is A Tape Measure Antenna Anyway?

August 14, 2022 by Dan Maloney 36 Comments

Amateur radio operators have played a longstanding game of “Will It Antenna?” If there’s something even marginally conductive and remotely resonant, a ham has probably tried to make an antenna out of it. Some of these expedient antennas actually turn out to be surprisingly effective, but as we can see from this in-depth analysis of the characteristics of tape measure antennas, a lot of that is probably down to luck.

At first glance, tape measure antennas seem to have a lot going for them (just for clarification, most tape measure antennas use only the spring steel blade of a tape measure, not the case or retraction mechanism — although we have seen that done.) Tape measures can be rolled up or folded down for storage, and they’ll spring back out when released to form a stiff, mostly self-supporting structure.

But [fvfilippetti] suspected that tape measures might have some electrical drawbacks, thanks to the skin effect. That’s the tendency for current to flow on the outside of a conductor, which at lower frequencies on conductors with a round cross-section turns out to be not a huge problem. But in a thin, rectangular conductor, a little finite element method magnetics (FEMM) analysis revealed that most of the current is carried in very small areas, resulting in high electrical resistance — an order of magnitude greater than a round conductor. Add in the high permittivity of the carbon steel material of the blade, and you end up something more like what [fvfilippetti] calls “a tape measure dummy load.

One possible solution: stripping the paint off the blade and copper plating it. It’s not clear if this was tried; we’d think it would be difficult to accomplish, but not impossible — and surely worth a try.

Remember DAB Radio? The Psion WaveFinder Gets A Teardown

August 13, 2022 by Jenny List 16 Comments

With digital music making a clean sweep in the 1990s over almost all listening media, it’s a surprise to find that there’s one area in which an analog hold-out is still very much alive and kicking. We’re talking not of a vinyl resurgence here but of FM radio, which has managed to effectively hold off its digital competition for a few decades now. Twenty years ago its days seemed numbered though, and in Europe the first generation of DAB digital radios looked ready to conquer the airwaves. Among them was a true oddity and one of Psion’s last significant consumer products, the WaveFinder USB DAB radio receiver. [Backofficeshow] has one, and has given it a teardown for our entertainment. He describes it as the first consumer SDR product which may be a little hyperbolic, but nevertheless, it’s an interesting look at what would become one of computing’s backwaters.

Inside the peak-90s-style translucent blue case is a single PCB with a lot of screening, on which sits a USB controller and a bunch of DSP chips. Radio demodulation was done in hardware, but signal demodulation was apparently done on the host PC. At the time its £299 price made it the affordable end of DAB reception, and The Register opined that its ability to download broadcast broadband data made it a revolutionary product, but sadly neither consumers nor broadcasters agreed and it was heavily discounted before making an ignominious exit. DAB itself would struggle to meet the expectations, and a multiplex-based licensing model for broadcasters making it unattractive to local stations means that even now FM is still full of stations. Perhaps as listening moves inexorably to streaming its time has passed, indeed Ireland has gone so far as to abandon DAB altogether.

If you’d like to know more about DAB, we took a look at the technology a while back.

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Testing A Laser Cut Wrench VS A Forged Wrench

August 13, 2022 by Al Williams 30 Comments

It is easy to not think much about common tools like screwdrivers and wrenches. But not for [Torque Test Channel]. The channel does a lot of testing of tools and in the video, below, they test a new wrench that is, oddly enough, laser cut instead of forged like the usual wrench.

You would expect a machined wrench to be weaker than a forged wrench. We were impressed, though, that there is so much difference between wrenches when you start making measurements.

Speaking of measurements, we would like to see more details of the test setups shown both in the video and in some of the video clips included. We did enjoy seeing the examination of the internal grain structure of both wrenches.

Be forewarned. Watching this video is likely going to send you to the computer to buy some new wrenches, especially if you don’t have 30/60 head wrenches.

The real question is why laser cut a wrench? It doesn’t seem like it is actually better than the forged variant. It is more expensive, but the setup costs for forging are higher. Particularly for a tool made in the United States, forging is both expensive and it is difficult to find time on the limited number of large-scale forges left in the country.

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The 286 Gives Up One Of Its Final Secrets

August 13, 2022 by Jenny List 115 Comments

Though it is largely forgotten today, the Intel 80286 was for a while in the 1980s the processor of choice and designated successor to the 8086 in the world of PCs. It brought a new mode that could address up to 16 Mb of memory, and a welcome speed boost over machines using an 8086 or 8088. As with many microprocessors, it has a few undocumented features, and it’s a couple of these that [rep lodsb] takes a look at. Along the way we learn a bit about the 286, and about why Intel had some of these undocumented instructions in the first place.

If you used a 286 it was probably as an end-user sitting in front of a PC-AT or clone. During manufacture and testing though, the processor had need of some extra functions, both for testing the chip itself and for debugging designs using it. It’s in these fields that the undocumented instructions sit, and they relate to an in-circuit emulator, a 286 with a debug port on some of its unused pins, which would have sat on a plug-in daughterboard for systems under test. The 286 was famous for its fancy extended mode taking rather a long time to switch to, and these instructions relate to loading and saving states before and after the switch.

The 286s time as the new hotness was soon blasted away by the 386 with its support for virtual memory, so for most of us it remains as simply a faster way that we ran 8086 code for a few years. They appear from time to time here, even being connected to the internet.

286 image: Thomas Nguyen (PttNguyen.net), CC BY-SA 4.0.

An Amstrad NC100 Has A New Purpose In Life

August 13, 2022 by Jenny List 3 Comments

We’re used to laptop computers featuring flip-up screens; this article is being written on one and it’s probable you’re reading it on another one. But there’s another laptop form factor that has gained legions of fans ever since the days of the TRS-80 Model 100, the flat slab with no hinge and both keyboard and display on its upper surface. It’s surfaced most recently in the DevTerm, which inspired [0x17] to have a go at building his own. Instead of starting from scratch though, he’s chosen to use the shell of an Amstrad NC100 from the 1990s.

This series of Amstrad portables followed the company’s tried and tested course of repackaging decade-old technology for the consumer market, and were Z80-based machines that shared much with the company’s PCW series of desktop wordprocessors. The character LCD, mainboard, and keyboard were replaced with a modern LCD, a Raspberry PI, and a custom ergonomic layout keyboard with all associated modules and cables.

The result is undeniably a neat flat form factor laptop computer, and one we could see ourselves using. There may be some questions relating to the repurposing of a retrocomputer when the same result could have been achieved with a bit of CAD work and a 3D printer, but perhaps the machine should speak for itself on that.

Meanwhile this isn’t the first Amstrad laptop we’ve seen recently, the company also did some unusually-shaped PCs in the 1990s.

How Do You Build A Tradition?

August 13, 2022 by Elliot Williams 6 Comments

I was struck by reading our writeup of the Zenit in Electronics contest – an annual event in the Slovak Republic – that it’s kind of like a decathlon for electronic engineers and/or hardware hackers. It’s a contest, in which students compete presumably initially on a local level, and then up to 32 at the national level. There’s a straight-up knowledge test, a complex problem to solve, and then a practical component where the students must actually fabricate a working device themselves, given a schematic and maybe some help. Reading through the past writeups, you get the feeling that it’s both a showcase for the best of the best, but also an encouragement for those new to the art. It’s full-stack hardware hacking, and it looks like a combination of hard work and a lot of fun.

What’s most amazing is that it’s in its 38th year. Think how much electronics, not to mention geopolitics, has changed in the last 40 years. But yet the Zenit competition still lives on. Since it’s mostly volunteer driven, with strong help from the Slovak electronics industry, it has to be a labor of love. What’s astounding to me is that this love has been kept alive for so long.

I think that part of the secret is that, although it’s a national competition, it’s possible to run it with a small yet dedicated crew. It’s certainly a worthwhile endeavor – I can only imagine how many young students’ lives have been impacted by the exposure to microelectronics hacking through the contest. Indeed, it’s telling that the current chairman of the competition, Daniel Valúch, was a competitor himself back in 1994.

I wonder if the people founding Zenit back in 1984 thought of themselves as creating a perpetual electronic engineering contest, or if they just wanted to try it out and it took on a life of its own? Could you start something like this today?

Air Filter DRM? Hacker Opts Out With NFC Sticker

August 13, 2022 by Donald Papp 55 Comments

[Flamingo-tech]’s Xiaomi air purifier has a neat safety feature: it will refuse to run if a filter needs replacement. Of course, by “neat” we mean “annoying”. Especially when the purifier sure seems to judge a filter to be useless much earlier than it should. Is your environment relatively clean, and the filter still has legs? Are you using a secondary pre-filter to extend the actual filter’s life? Tough! Time’s up. Not only is this inefficient, but it’s wasteful.

Every Xiaomi filter contains an NTAG213 NFC tag with a unique ID and uses a unique password for communications, but how this password was generated (and therefore how to generate new ones) was not known. This meant that compatible tags recognized by the purifier could not be created. Until now, that is. [Flamingo-tech] has shared the discovery of how Xiaomi generates the password for communication between filter and purifier.

A small NFC sticker is now all it takes to have the purifier recognize a filter as new.

[Flamingo-tech] has long been a proponent of fooling Xiaomi purifiers into acting differently. In the past, this meant installing a modchip to hijack the DRM process. That’s a classic method of getting around nonsense DRM on things like label printers and dishwashers, but in this case, reverse-engineering efforts paid off.

It’s now possible to create simple NFC stickers that play by all the right rules. Is a filter’s time up according to the NFC sticker, but it’s clearly still good? Just peel that NFC sticker off and slap on a new one, and as far as the purifier is concerned, it’s a new filter!

If you’re interested in the reverse-engineering journey, there’s a GitHub repository with all the data. And for those interested in purchasing compatible NFC stickers, [Flamingo-tech] has some available for sale.