Fail of the Week: How Not to Design an RF Signal Generator

We usually reserve the honor of Fail of the Week for one of us – someone laboring at the bench who just couldn’t get it together, or perhaps someone who came perilously close to winning a Darwin Award. We generally don’t highlight commercial products in FotW, but in the case of this substandard RF signal generator, we’ll make an exception.

We suppose the fail-badge could be pinned on [electronupdate] for this one in a way; after all, he did shell out $200 for the RF Explorer signal generator, which touts coverage from 24 MHz to 6 GHz. But in true lemons-to-lemonade fashion, the video below he provides us with a thorough analysis of the unit’s performance and a teardown of the unit.

The first step is a look at the signal with a spectrum analyzer, which was not encouraging. Were the unit generating a pure sine wave as it should, we wouldn’t see the forest of spikes indicating harmonics across the band. The oscilloscope isn’t much better; the waveform is closer to a square wave than a sine. Under the hood, he found a PIC microcontroller and a MAX2870 frequency synthesizer, but a conspicuous absence of any RF filtering components, which explains how the output got so crusty. Granted, $200 is not a lot to spend compared to what a lab-grade signal generator with such a wide frequency range would cost. And sure, external filters could help. But for $200, it seems reasonable to expect at least some filtering.

We applaud [electronupdate] for taking one for the team here and providing some valuable tips on RF design dos and don’ts. We’re used to seeing him do teardowns of components, like this peek inside surface-mount inductors, but we like thoughtful reviews like this too.

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Electric Shower Head Teardown Makes Us Wince

We have bought some really amazing stuff from the Chinese online shops. We’ve also bought stuff that was… less than satisfactory, let’s say. At the prices you pay, you usually just chalk up the bad stuff as a cost of doing business. But [DiodeGoneWild] has a teardown of something that could be very dangerous if it wasn’t up to snuff: an electrically heated shower head. He says they are common in Latin America and have the nickname “suicide showers.”

We’ve seen the cute showerheads that change color, but those take batteries. What we are talking about here connects to the 220V main and draws 30A to instantly heat your shower water. Environmentally, that’s great since you don’t have a tank of water you keep heating and reheating just in case you need hot water. But you wouldn’t throw an AC radio in the tub, so you have to wonder just how safely this thing’s built. Well, you don’t have to wonder, because the videos below are going to show us.

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A Radar Module Teardown And Measuring Fan Speed The Hard Way

If you have even the slightest interest in microwave electronics and radar, you’re in for a treat. The Signal Path is back with another video, and this one covers the internals of a simple 24-GHz radar module along with some experiments that we found fascinating.

The radar module that [Shahriar] works with in the video below is a CDM324 that can be picked up for a couple of bucks from the usual sources. As such it contains a lot of lessons in value engineering and designing to a price point, and the teardown reveals that it contains but a single active device. [Shahriar] walks us through the layout of the circuit, pointing out such fascinating bits as capacitors with no dielectric, butterfly stubs acting as bias tees, and a rat-race coupler that’s used as a mixer. The flip side of the PCB has two arrays of beam-forming patch antennas, one for transmit and one for receive. After a few simple tests to show that the center frequency of the module is highly variable, he does a neat test using gimbals made of servos to sweep the signal across azimuth and elevation while pointing at a receiving horn antenna. This shows the asymmetrical nature of the beam-forming array. He finishes up by measuring the speed of a computer fan using the module, which has some interesting possibilities in data security as well as a few practical applications.

Even though [Shahriar]’s video tend to the longish side, he makes every second count by packing in a lot of material. He also makes complex topics very approachable, like what’s inside a million-dollar oscilloscope or diagnosing a wonky 14-GHz spectrum analyzer.

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Failed Tool Turned Exploded Wall Art

Few things hit a hacker or maker harder than when a beloved tool goes to that Big Toolbox In The Sky. It can be hard to trash something that’s been with you through countless repairs and teardowns, made all the worse by the fact most employers don’t recognize “Tool Bereavement” as a valid reason to request time off. Maybe next time one of your trusty pieces of gear gives up the ghost, you can follow the example set by [usuallyplesent] and turn it into a piece of art to hang up on the shop wall.

The shop had gotten years of daily service out of this air powered angle die grinder (not bad for a $14 Harbor Freight tool), and he thought they should immortalize it in their waiting room by turning it into an interesting piece of art. After all, it’s not everyday that some folks see the insides of the sort of tools the more mechanically inclined of us may take for granted.

After taking the grinder apart and cleaning everything up, [usuallyplesent] decided to simplify things a bit by tossing out the assorted tiny components like seals and washers. By just focusing on the larger core components, the exploded view is cleaner and reminds us of a light saber cutaway.

Using a piece of scrap cardboard, [usuallyplesent] made templates for all of the major pieces of the grinder and used that to sketch out the placement and spacing on the white background. He then cut out each shape so the parts would be partially recessed into the board. This gives the effect that each piece was cut down the middle lengthwise but without all the hassle of actually cutting everything down the middle lengthwise.

We’ve previously seen similar displays made out of dissected consumer electronics, but there’s something rather personal about doing the same thing for a well-used tool. If any of our beloved readers feel inspired to enshrine a dead multimeter into a shadow box over the bench, be sure to let us know.

[via /r/justrolledintotheshop]

Teardown Of A Fingerprint Padlock

We wouldn’t mind tearing down a fingerprint scanner, but we hate to bust up our expensive laptop or cell phone. [Julian], however, got a hold of a fingerprint scanning padlock and was willing to tear it apart for our benefit. The video appears below.

The padlock is a simple enough little device with a cable lock instead of a solid metal shackle, although we have seen similar devices with traditional shackles. Initially, the lock’s fingerprint storage is empty and it will open for any fingerprint. The first task is to set an administrator fingerprint. You’ll need that fingerprint to set up other fingerprints or to reset the unit. Of course, what we are really interested in is what’s inside.

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A Stereo Tube Amp For Less Than $5

Many of us have aspirations of owning a tube amp. Regardless of the debate on whether or not tube audio is nicer to listen to, or even if you can hear the difference at all, they’re gorgeous to look at. However, the price of buying one to find out if it floats your boat is often too high to justify a purchase.

A motor transformer

[The Post Apocalyptic Inventor] has built a stereo tube amplifier in the style of the Fallout video games. The idea came when he realised that the TK 125 tape recorder manufactured by Grundig was still using tube audio in the late 60s. What’s more, they frequently sell on eBay for 1-10€ in Germany. [TPAI] was able to salvage the main power amplifier from one of these models, and restore it so that it could be re-purposed and see use once more.

The teardown of the original cassette recorder yields some interesting parts. Firstly, an integrated motor transformer — an induction motor whose stator acts as the magnetic core of the transformer responsible for the tube electronics. There’s also an integrated capacitor which contains three separate electrolytics. The video after the break is well worth a watch (we always find [TPAI]’s videos entertaining).

A new chassis is created out of a steel base plate and aluminium angle, and some neat frames for the motor transformers are made from scrap copper wire bent and soldered together. It looks great, though there’s always the option to use a cake tin instead.

If you’re interested in the design of tube amps, we’ve covered heaps of cool builds: from this low-voltage design to this tiny guitar amp, or even ones using tubes which are flat.

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Milspec Teardown: C-1282 Chaff Controller

A B-52 bomber is approaching its primary target: rail yards in the Beloostrov district of Leningrad. Intel reports the area is likely defended by S-25 Berkut and S-75 Dvinia surface to air missiles (SAMs), but this close to the target the gigantic bomber can’t afford to make the evasive maneuvers, known as combat turns, which would help shake off enemy air defenses. From his position behind the co-pilot, the electronic warfare officer (EWO) reaches over and sets the C-1282 for continuous chaff ejection. Hundreds of thin metallic strips are jettisoned from the B-52, confusing tracking radar and allowing the bomber and her crew to slip through the Soviet air defenses and drop 50,000 lbs of ordnance directly onto the target.

Luckily for all of us, this event never actually occurred. But it was a possibility that the United States and Soviet Union had prepared for extensively. Both sides developed ever more capable weapons, and for each new weapon, a new countermeasure was invariably created. The C-1282 is a component of one such countermeasure, a device that allowed the B-52’s EWO to configure and monitor the bomber’s automatic chaff dispenser. With the C-1282 handling the anti-radar countermeasures, the bomber’s crew could focus their attention on completing their mission.

Of course, as is the case with technology (military or otherwise), the C-1282 was eventually phased out for something new. These old units, now largely worthless, were destroyed or sentenced to a lifetime collecting dust on a storeroom shelf. But through the magic of the Internet, one of these devices is now ready to be laid bare for your viewing pleasure. Dust off your Joseph McCarthy Junior Detective badge and come along as we take a look at a state of the art piece of Anti-Ruskie technology, circa 1960.

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