Aluminum Foil 20 Cm Antenna For 10 M Operation

July 2, 2022 by Chris Lott 11 Comments

[David], DL1DN, is an Amateur Radio enthusiast with a penchant for low-power (QRP) portable operations. Recently he was out and about, and found that 10 m propagation was wide open. Not discouraged by having forgotten his antenna, he kludges up a makeshift one using a 20 cm length of aluminum foil (see video demonstration below the break). [David] wasn’t completely unprepared, as he did have the loading coil for his portable 20 m antenna, but was missing the telescoping whip. He calculated the whip length should be around 20 cm for 10 m operation, and crinkles up a sheet of foil the approximate length. He tunes it to length by rolling the tip to shorten the “whip” until he gets an SWR minimum.

Schematic of [David]’s QRP Portable Whip Antenna

[David] describes this style of portable antenna in another video, using a more conventional telescoping whip as the radiating element. The loading coil is built from common PVC pipe and insulated wire. While these aren’t necessarily the most efficient antennas, they can do the trick when portability is a major concern. For a different approach, here’s a QRP Hackaday.io portable antenna project using a magnetic loop antenna. But for the ultimate in QRP, check out this transmitter we wrote about in 2013 that uses only voice power to operate.

What are some unusual items you’ve used as makeshift antennas? Let us know in the comments below. Thanks to [mister35mm] for submitting this to our tip line.

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Dual Power Supply In A Pinch

July 2, 2022 by Chris Lott 14 Comments

Recently I needed a dual voltage power supply to test a newly-arrived PCB, but my usual beast of a lab power supply was temporarily at a client’s site. I had a FNIRSI programmable power supply which would have been perfect, but alas, I had only one. While digging around in my junk box I found several USB-C power-delivery “trigger” boards which I bought for an upcoming project. These seemed almost too small for the task at hand, but after a little research I realized they would work quite well.

The ones I had used the Injoinic IP2721 USB-C power delivery chip, commonly used in many of these boards. Mine had been sold pre-configured for certain output voltages, but they were easy to re-jumper to the voltages I needed, +5 VDC and +20 VDC. The most challenging aspect was physically using them — they are the size of a fingernail. This version had through-hole output pads on 0.1″ centers, so I decided to solder them to the base of a standard MTA pin header. A few crimps later and I was up and running, along with the requisite pair of USB-C cables and power adapters.

For just a few dollars each, these trigger boards are useful to have in your toolbox, both for individual projects and for use in a pinch. We reviewed these modules a couple of years ago, and check out the far more flexible PD Micro that we covered last year.

Mysterious Adder From 1960s Bendix G-20

June 24, 2022 by Chris Lott 8 Comments

[David Lovett] aka Usagi Electric is taking a dive into yet another old computer design, this one from the early 1960s. He recently obtained eight mystery circuit boards on-loan for the purpose of reverse engineering them. It turns out these came from an old mainframe called the Bendix G-20, a successor to the 1965 G-15 vacuum tube model. The cards are:

Full Adder
AND Gate
OR Gate
Emitter Follower
Flip Flop
Quad Inverting Amplifier
DLO Amplifier
Gated CPA

Most of these are pretty straightforward to figure out, but he ran into some troubles trying to understand the full adder board. The first issue is there is some uncertainty surrounding the logic level voltages. This system uses negative voltages, with -3.5 V representing a logic 1 … or is it a logic 0? And even taking into account this ambiguity, [David] is having a hard time deciphering how the adder works. It uses a bunch of diodes to implement a logic lookup table of an adder — except he is not able to make it match any known addition scheme. [David] has called out to the community for help on this one, and if you have any ideas how this adder works, visit his wiki linked above for more information and give him shout.

We don’t know how [David] squeezes in the time for these side projects, when he is so busy on the Centurion mini-computer restoration and the monstrous single-bit vacuum tube computer he is building.

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South Korea’s KSLV-2 Rocket Delivers Payloads To Orbit

June 23, 2022 by Chris Lott 5 Comments

South Korea’s domestically developed KSLV-2 “Nuri” rocket successfully placed six payloads into low Earth orbit Tuesday, after lifting off from from Naro Space Center at 4 PM KST. This follows an earlier attempt in October which failed to reach orbit after the booster’s third stage engine shutdown prematurely. The flight followed an initial trajectory over the East China Sea, after which the upper stage steered out towards the Philippine Sea, finally placing the payload in the desired orbital inclination of 98 degrees. This less-than-ideal path wasted energy, but ensured that the first and second stages fell into the ocean and not onto people. Success was confirmed shortly after launch as the vehicle passed over South Korea’s King Sejong Station in Antarctica.

The payload on this test flight was primarily a mass simulator of 1.3 metric tons, but a small Performance Verification Satellite (PVSAT) was included, for a grand total of 1.5 metric tons. The PVSAT itself monitors vehicle performance, but also serves as a carrier for four CubeSats. These were developed by engineering teams at various local universities and will be deployed in the coming days.

If you’re inclined to track these, the launch has been given COSPAR ID 2022-065 and the first three objects (third stage, dummy mass, and PVSAT) have been assigned the NORAD catalog numbers 52894, 52895, and 52896. It’s too early to tell which is which at this point, but as more data about their respective orbits are collected, it should be possible to tell them apart. The next four catalog numbers, 52897 – 52900, have been reserved for the CubeSats once they are released.

With this launch, South Korea has become the 10th nation to put a payload into space using its own domestic technology, and the 7th to loft a payload of more than one ton to orbit — joining the ranks of the United States, Russia, Japan, China, France, and India.

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Remoticon 2021 // Rob Weinstein Builds An HP-35 From The Patent Up

April 7, 2022 by Chris Lott 40 Comments

Fifty years ago, Hewlett-Packard introduced the first handheld scientific calculator, the HP-35. It was quite the engineering feat, since equivalent machines of the day were bulky desktop affairs, if not rack-mounted. [Rob Weinstein] has long been a fan of HP calculators, and used an HP-41C for many years until it wore out. Since then he gradually developed a curiosity about these old calculators and what made them tick. The more he read, the more engrossed he became. [Rob] eventually decided to embark on a three year long reverse-engineer journey that culminated a recreation of the original design on a protoboard that operates exactly like the original from 1972 (although not quite pocket-sized). In this presentation he walks us through the history of the calculator design and his efforts in understanding and eventually replicating it using modern FPGAs.

The HP patent ( US Patent 4,001,569 ) contains an extremely detailed explanation of the calculator in nearly every aspect. There are many novel concepts in the design, and [Rob] delves into two of them in his presentation. Early LED devices were a drain on batteries, and HP engineers came up with a clever solution. In a complex orchestra of multiplexed switches, they steered current through inductors and LED segments, storing energy temporarily and eliminating the need for inefficient dropping resistors. But even more complicated is the serial processor architecture of the calculator. The first microprocessors were not available when HP started this design, so the entire processor was done at the gate level. Everything operates on 56-bit registers which are constantly circulating around in circular shift registers. [Rob] has really done his homework here, carefully studying each section of the design in great depth, drawing upon old documents and books when available, and making his own material when not. For example, in the course of figuring everything out, [Rob] prepared 338 pages of timing charts in addition to those in the patent. Continue reading “Remoticon 2021 // Rob Weinstein Builds An HP-35 From The Patent Up” →

Galaxy Users Accuse Samsung Of Throttling Performance And Benchmark Rigging

March 10, 2022 by Chris Lott 24 Comments

A lot of Samsung Galaxy users think that Samsung has been throttling smartphone performance, so much so that they don’t live up to their published specifications. At issue is the game optimizing service (GOS) which is intended to throttle the CPU while playing games to prevent overheating. S22 owners have recently discovered that it’s not only games that are throttled, but there’s a list of over 10,000 apps which are subject to GOS control, and there is no way to disable it.

What they’re really upset over is the fact that popular benchmarking apps are not subject to GOS throttling — something that’s hard to see as anything but a blatant attempt to game the system. In fact, this past weekend the folks at Geekbench banned four generations of Samsung Galaxy phones (S10, S20, S21, S22) for benchmark manipulation.

Admittedly, thermal management is critical on today’s incredibly powerful handheld devices, and the concept of throttling is an accepted solution in the industry. But people are upset at the opaqueness and lack of control of GOS, not to mention cherry picking apps in order to excel at benchmarks. Furthermore Samsung has removed their vapor chamber cooling system from recent models. This makes GOS even more important and looks like a cost-savings measure that may have backfired. Currently there’s a petition with the government claiming false advertising, and users are actively pursuing a lawsuit against Samsung.

Kia Recalls Cars Over Airbag Controller Assembly Issue

March 9, 2022 by Chris Lott 26 Comments

Last month Kia Motors announced a large recall due to possibly defective airbag controller units (ACU). The recall spans many models and model years — in the United States alone it covers over 400K cars, and over half a million cars worldwide. From the NHTSA report we learn that the problem happened at assembly when the cover of some ACUs interfered with the pins of an EEPROM chip. This can cause some of the pins to open-circuit. If your car had this problem, a warning light would come on, but more seriously, the airbags would not deploy in an accident. Kia estimates that less than 1% of the cars using this ACU have this issue. Cars which have this fault will get a new ACU, and other cars will get a firmware upgrade to keep this from happening should the EEPROM pins break loose in the future.

We think this EEPROM is used for logging errors and crash events, and is therefore not in the critical path for airbag deployment. The original firmware apparently prevented deployment if the EEPROM had a fault. Presumably, after this patch, if pins break in the future, the fault indicator still lights up but you’ll have functioning airbags.

It’s not clear if these broken EEPROM pin solder joints were present from the start and the factory test procedures didn’t catch the problem. Or did the pins left the factory intact and were subsequently broke due to bumps and vibrations. Hardware issues aside, having safety critical firmware perform its primary function even when faults exist in non-essential parts of the circuit seems like a requirement that should have been applied to the ACU from the beginning.

This is a reminder of the importance of enclosure design and making sure your PCB layouts take into account all clearances necessary for the entire assembly. How many times have you got your PCB back and realized you forgot to even put mounting holes?

We covered a similar issue a couple of years ago regarding the Takata airbag fiasco. If you have a Kia, this form on their website tells you whether your vehicle is subject to the recall or not.