Aluminum Foil 20 Cm Antenna For 10 M Operation

[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 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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Does Hot Water Freeze Faster Than Cold? Debate Continues Over The Mpemba Effect

Does hot water freeze faster than cold water? On its face this idea seems like it should be ridiculously simple to test, and even easier to intuit, but this question has in fact had physicists arguing for decades.

Erasto Mpemba’s observations initiated decades of research into the Mpemba effect: whether a liquid (typically water) which is initially hot can freeze faster than the same liquid which begins cold.

There’s a name for the phenomenon of something hot freezing faster than something cold: the Mpemba effect,  named for Erasto Mpemba (pictured above) who as a teenager in Tanzania witnessed something strange in high school in the 1960s. His class was making ice cream, and in a rush to secure the last available ice tray, Mpemba skipped waiting for his boiled milk-and-sugar mixture to cool to room temperature first, like everyone else had done. An hour and a half later, his mixture had frozen into ice cream whereas the other students’ samples remained a thick liquid slurry.

Puzzled by this result, Mpemba asked his physics teacher what was going on. He was told “You were confused. That cannot happen.” Mpemba wasn’t convinced by that answer, and his observations ultimately led to decades of research.

What makes this question so hard to nail down? Among many of the issues complicating exactly how to measure such a thing is that water frankly has some odd properties; it is less dense as a solid, and it is also possible for its solid and liquid phases to exist at the same temperature. Also, water in the process of freezing is not in equilibrium, and how exactly things act as they relax into equilibrium is a process for which — physics-wise — we lack a good theory. Practically speaking, it’s also a challenge how to even accurately and meaningfully measure the temperature of a system that is not in equilibrium.

But there is experimental evidence showing that the Mpemba effect can occur, at least in principle. How this can happen seems to come down to the idea that a hot system (having more energy) is able to occupy and explore more configurations, potentially triggering states that act as a kind of shortcut or bypass to a final equilibrium. In this way, something that starts further away from final equilibrium could overtake something starting from closer.

But does the Mpemba effect actually exist — for example, in water — in a meaningful way? Not everyone is convinced, but if nothing else, it has sure driven a lot of research into nonequilibrium systems.

Why not try your own hand at investigating the Mpemba effect? After all, working to prove someone wrong is a time-honored pastime of humanity, surpassed only in popularity by the tradition of dismissing others’ findings, observations, or results without lifting a finger of your own. Just remember to stick to the scientific method. After all, people have already put time and effort into seriously determining whether magnets clean clothes better than soap, so surely the Mpemba effect is worth some attention.

Farm Data Relay System: Combine LoRa And 2.4 Ghz Networks Without WiFi Routers And Cloud Dependence

Setting up a wireless sensor network over a wide area can quickly become costly, and making everything communicate smoothly can be a massive headache, especially when you’re combining short range Wi-Fi with long range LoRa. To simplify this, [Timm Bogner] created Farm Data Relay System which simplifies the process of combining LoRa, 2.4Ghz modules and serial communications in various topologies over wide areas.

The FDRS uses a combination of ESP32/8266 sensor nodes for short range, and LoRa nodes for long range. The ESP nodes use Espressif’s connectionless ESP-NOW peer-to-peer protocol on which allow multiple ESP boards to communicate directly without the need for a Wi-Fi router. The ESP modules can have one of 3 roles, nodes, repeaters or gateways, and gateways and repeaters share the same code. Nodes take sensor inputs, and are configured to each have a unique READING_ID.

Relays just retransmit ESP-NOW packets to extend the network range, while gateways convert packets between ESP-NOW, MQTT over Wi-Fi, LoRa or serial messages as required. Repeaters and gateways each have a unique UNIT_MAC for addressing. The code that handles communication for the ESP devices is simple and well documented, so you only need to set a few configuration values, and then can focus your efforts on the code required for your specific application.

The hub of the system is a Raspberry Pi running Node-RED which acts as the final MQTT gateway and connects to the ESP MQTT gateways. This means that all the action happens in the local network, without being dependent on an internet connection and cloud service. However, it can still send and receive data over the internet using MQTT or any other protocol as required. Node-RED makes it particularly easy to build custom automations and interfaces.

In the video after the break, Andreas Spiess, the man with the Swiss accent, who also has a hand in the project, goes over all the features, setup and caveats.

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An Anodiser That Does Gradients

Anodizing aluminium, the process of electrolytic build up of the metal’s the oxide layer in the presence of dyes to create colored effects, is such a well-established process that we probably all have anodized items within sight. It’s usually an industrial mass-production process that creates a uniform result, but there’s an anodizing machine from a Dutch design studio which promises to place anodized aluminium in a new light. Studio Loop Loop’s Magic Color Machine enacts a small-scale automated anodizing process driven by a microcontroller, and is capable of effects such as gradated colors.

Unfortunately their website is long on marketing and short on technical details, but the basic function of a line of chemical baths with a pulley to lower and lift the item being anodized shouldn’t be too difficult for any Hackaday reader to understand. There’s a short video clip posted on Instagram which also gives some idea. It’s a powerful idea that should lead to some eye-catching work for their studio, but its interest here lies in the techniques it might inspire others to try. We look forward to an open-source version of a gradated anodize. Meanwhile if anodizing takes your fancy, it’s a subject we’ve visited before.

An Affordable Reference Mic You Can Build Yourself

Reference mics are vital tools for audio work. They’re prized for their flat frequency response, and are often used for characterizing the audio response of a room or space. OpenRefMic aims to be an open source design for producing reference mics without paying exorbitant retail prices.

The heart of the build is a preamplifier that runs off standard 48 V phantom power, and is responsible for both biasing the electret microphone element and acting as a buffer for the mic signal. It’s designed specifically to work with the PUI AOM-5024L-HD-F-R mic capsule, chosen for its good performance and low noise characteristics. However, other electric mics should work, too. The hardware is wrapped up in a 3D printed case which can readily be made on most basic printers. It’s complete with a press-fit grille that holds the mic capsule in place.

The prime goal of the project is low noise; the project creator, [loudifier], notes that most commercial reference mics focus first on flat frequency response and then reducing noise. OpenRefMic performs well in this area, and its lack of a perfectly flat frequency response is countered with calibrated equalization. It also works with regular pro-grade XLR cables and phantom power, rather than needing fancy laboratory-spec cables and interfaces.

The final result is a credit to [loudifier], who demonstrates a strong understanding of the principles of reference mic design. We’ve seen some other great low-cost reference mics recently, too!

Not On The Internet

Whenever you need to know something, you just look it up on the Internet, right? Using the search engine of your choice, you type in a couple keywords, hit enter, and you’re set. Any datasheet, any protocol specification, any obscure runtime error, any time. Heck, you can most often find some sample code implementing whatever it is you’re looking for. In a minute or so.

It is so truly easy to find everything technical that I take it entirely for granted. In fact, I had entirely forgotten that we live in a hacker’s utopia until a couple nights ago, when it happened again: I wanted to find something that isn’t on the Internet. Now, to be fair, it’s probably out there and I just need to dig a little deeper, but the shock of not instantly finding the answer to a random esoteric question reminded me how lucky we actually are 99.99% of the time when we do find the answer straight away.

So great job, global hive-mind of über-nerds! This was one of the founding dreams of the Internet, that all information would be available to everyone anywhere, and it’s essentially working. Never mind that we can stream movies or have telcos with people on the other side of the globe – when I want a Python library for decoding Kansas City Standard audio data, it’s at my fingertips. Detailed SCSI specifications? Check.

But what was my search, you ask? Kristina and I were talking about Teddy Ruxpin, and I thought that the specification for the servo track on the tape would certainly have been reverse engineered and well documented. And I’m still sure it is – I was just shocked that I couldn’t instantly find it. The last time this happened to me, it was the datasheet for the chips that make up a Speak & Spell, and it turned out that I just needed to dig a lot harder. So I haven’t given up hope yet.

And deep down, I’m a little bit happy that I found a hole in the Internet. It gives Kristina and me an excuse to reverse engineer the format ourselves. Sometimes ignorance is bliss. But for the rest of those times, when I really want the answer to a niche tech question, thanks everyone!

Dual Power Supply In A Pinch

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.