RF

194 Articles

A Modern Take On A Piece Of Old Test Equipment

December 15, 2019 by No comments

The HP 11947A is something of a footnote in the back catalogue of Hewlett Packard test equipment. An attenuator and limiter with a bandwidth in the megahertz rather than the gigahertz. It’s possible that few laboratories have much use for one in 2019, but it does have one useful property: a full set of schematics and technical documentation. [James Wilson] chose the device as the subject of a clone using surface mount devices.

The result is very satisfyingly within spec, and he’s run a battery of tests to prove it. As he says, the HP design is a good one to start with.   As a device containing only passive components and with a maximum frequency in the VHF range this is a project that makes a very good design exercise for anyone interested in RF work or even who wishes to learn a bit of RF layout. At these frequencies there are still a significant number of layout factors that can affect performance, but the effect of conductor length and  stray capacitance is less than the much higher frequencies typically used by wireless-enabled microcontrollers.

Hackaday Superconference: An Analog Engineer Dives Into RF

December 9, 2019 by 6 Comments

Those of us who work with electronics will usually come to the art through a particular avenue that we master while imbibing what we need from those around it. For example, an interest in audio circuitry may branch into DSP and microcontrollers as projects become more complex. Some realms though retain an aura of impossibility, a reputation as a Dark Art, and chief among them for many people is radio frequency (RF). Radio circuitry is often surprisingly simple, yet that simplicity conceals a wealth of complexity because the medium does not behave in the orderly manner of a relatively static analogue voltage or a set of low-frequency logic levels.

Chris Gammell is a familiar face to many Hackaday readers for his mastery of much electronic trickery, so it comes as something of a surprise to find that RF has been one of the gaps in his knowledge. In his talk at the Hackaday Superconference he took us through his journey into RF work, and the result is a must-watch for anyone with a curiosity about radio circuitry who didn’t know where to start.

Continue reading “Hackaday Superconference: An Analog Engineer Dives Into RF” →

Hacking Transmitters, 1920s Style

November 28, 2019 by 9 Comments

The origin of the term “breadboard” comes from an amusing past when wooden bread boards were swiped from kitchens and used as a canvas for radio hobbyists to roll homemade capacitors, inductors, and switches. At a period when commercial electronic components were limited, anything within reach was fair game.

[Andy Flowers], call sign K0SM, recently recreated some early transmitters using the same resources and techniques from the 1920s for the Bruce Kelley 1929 QSO Party. The style of the transmitters are based on [Ralph Hartley]’s oscillator circuit built for Bell Telephone in 1915. Most of the components he uses are from the time period, and one of the tubes he uses is even one of four tubes from the first Transatlantic contact in 1923.

Apart from vacuum tubes (which could be purchased) and meters (which could be scrounged from automobiles) [Flowers] recreated his own ferrite plate and outlet condensers for tuning the antennas. The spiderweb coils may not be as common today, but can be found in older Crosley receivers and use less wire than comparable cylindrical coils.

A number of others features of the transmitters also evoke period nostalgia. The coupling to the antenna can be changed using movable glass rods, although without shielding there are quite a number of factors to account for. A vertical panel in the 1920s style also shows measurements from the filament, plate current, and antenna coupling.

While amature radio has become increasingly high-tech over the last few years, it’s always good to see dedicated individuals keeping the old ways alive; no matter what kind of technology they’re interested in.

Continue reading “Hacking Transmitters, 1920s Style” →

Raspberry Pi 4 HDMI Is Jamming Its Own WiFi

November 28, 2019 by 87 Comments

Making upgrades to a popular product line might sound like a good idea, but adding bigger/better/faster parts to an existing product can cause unforeseen problems. For example, dropping a more powerful engine in an existing car platform might seem to work at first until people start reporting that the increased torque is bending the frame. In the Raspberry Pi world, it seems that the “upgraded engine” in the Pi 4 is causing the WiFi to stop working under specific circumstances.

[Enrico Zini] noticed this issue and attempted to reproduce exactly what was causing the WiFi to drop out, and after testing various Pi 4 boards, power supplies, operating system version, and a plethora of other variables, the cause was isolated to the screen resolution. Apparently at the 2560×1440 setting using HDMI, the WiFi drops out. While you could think that an SoC might not be able to handle a high resolution, WiFi, and everything else this tiny computer has to do at once. But the actual cause seems to be a little more interesting than a simple system resources issue.

[Mike Walters] on a Twitter post about this issue probed around with a HackRF and discovered a radio frequency issue. It turns out that at this screen resolution, the Pi 4 emits some RF noise which is exactly in the range of WiFi channel 1. It seems that the Pi 4 is acting as a WiFi jammer on itself.

This story is pretty new, so hopefully the Raspberry Pi Foundation is aware of the issue and working on a correction. For now, though, it might be best to run a slightly lower resolution if you’re encountering this problem.

Hackaday Links Column Banner

Hackaday Links: November 17, 2019

November 17, 2019 by 8 Comments

Friday, November 15, 2019 – PASADENA. The 2019 Hackaday Superconference is getting into high gear as I write this. Sitting in the Supplyframe HQ outside the registration desk is endlessly entertaining, as attendees pour in and get their swag bags and badges. It’s like watching a parade of luminaries from the hardware hacking world, and everyone looks like they came ready to work. The workshops are starting, the SMD soldering challenge is underway, and every nook and cranny seems to have someone hunched over the amazing Hackaday Superconference badge, trying to turn it into something even more amazing. The talks start on Saturday, and if you’re not one of the lucky hundreds here this weekend, make sure you tune into the livestream so you don’t miss any of the action.

The day when the average person is able to shoot something out of the sky with a laser is apparently here. Pablo, who lives in Argentina, has beeing keeping tabs on the mass protests going on in neighboring Chile. Huge crowds have been gathering regularly over the last few weeks to protest inequality. The crowd gathered in the capital city of Santiago on Wednesday night took issue with the sudden appearance of a police UAV overhead. In an impressive feat of cooperation, they trained 40 to 50 green laser pointers on the offending drone. The videos showing the green beams lancing through the air are quite amazing, and even more amazing is the fact that the drone was apparently downed by the lasers. Whether it was blinding the operator through the FPV camera or if the accumulated heat of dozens of lasers caused some kind of damage to the drone is hard to say, and we’d guess that the drone was not treated too kindly by the protestors when it landed in the midsts, so there’s likely not much left of the craft to do a forensic analysis, which is a pity. We will note that the protestors also trained their lasers on a police helicopter, an act that’s extremely dangerous to the human pilots which we can’t condone.

In news that should shock literally nobody, Chris Petrich reports that there’s a pretty good chance the DS18B20 temperature sensor chips you have in your parts bin are counterfeits. Almost all of the 500 sensors he purchased from two dozen vendors on eBay tested as fakes. His Github readme has an extensive list that lumps the counterfeits into four categories of fake-ness, with issues ranging from inaccurate temperature offsets to sensors without EEPROM that don’t work with parasitic power. What’s worse, a lot of the fakes test almost-sorta like authentic chips, meaning that they may work in your design, but that you’re clearly not getting what you paid for. The short story to telling real chips from the fakes is that Maxim chips have laser-etched markings, while the imposters sport printed numbers. If you need the real deal, Chris suggests sticking with reputable suppliers with validated supply chains. Caveat emptor.

A few weeks back we posted a link to the NXP Homebrew RF Design Challenge, which tasked participants to build something cool with NXP’s new LDMOS RF power transistors. The three winners of the challenge were just announced, and we’re proud to see that Razvan’s wonderfully engineered broadband RF power amp, which we recently featured, won second place. First place went to Jim Veatch for another broadband amp that can be built for $80 using an off-the-shelf CPU heatsink for thermal management. Third prize was awarded to a team lead by Weston Braun, which came up with a switch-mode RF amp for the plasma cavity for micro-thrusters for CubeSats, adorably named the Pocket Rocket. We’ve featured similar thrusters recently, and we’ll be doing a Hack Chat on the topic in December. Congratulations to the winners for their excellent designs.

Well-Engineered RF Amplifier Powers Ham Radio Contacts

November 7, 2019 by 35 Comments

Typically, amateur radio operators use the minimum power needed to accomplish a contact. That’s just part of being a good spectrum citizen, and well-earned bragging rights go to those who make transcontinental contacts on the power coming from a coin cell. But sometimes quantity has a quality all its own, and getting more power into the ether is what the contact requires. That’s where builds such as this well-engineered 600W broadband RF amplifier come into play.

We’re really impressed with the work that [Razvan] put into this power amp. One of the great joys of being a ham is being able to build your own gear, and to incorporate the latest technology long before the Big Three manufacturers start using it. While LDMOS transistors aren’t exactly new – laterally-diffused MOSFETs have been appearing in RF power applications for decades – the particular parts used for the amp, NXP’s MRF300 power transistors, are pretty new to the market. A pair of the LDMOS devices form the heart of the push-pull amp, as do an array of custom-wound toroids and transformers including a transmission line transformer wound with 17-ohm coax cable. [Razvan] paid a lot of attention to thermal engineering, too, with the LDMOS transistors living in cutouts in the custom PCB so they can mate with a hefty heatsink. Even the heatsink compound is special; rather than the typical silicone grease, he chose a liquid metal alloy called Gallinstan. The video below gives a tour of the amp and shows some tests with impressive results.

Continue reading “Well-Engineered RF Amplifier Powers Ham Radio Contacts” →

Hackaday Links Column Banner

Hackaday Links: September 29, 2019

September 29, 2019 by 6 Comments

In a sure sign that we’ve arrived in the future, news from off-world is more interesting this week than Earth news. When the InSight probe landed on Mars last year, it placed the first operating magnetometer on the Red Planet. Since then, the sensitive instrument has been logging data about the planet’s magnetic field, and now there are reports that researchers have discovered a chain of pulsations in the magnetic field. Pulsations in planetary magnetic fields aren’t all that strange; pulse trains that occur only at Martian midnight are, though. Researchers haven’t got a clue yet about what this means. We assume they’ve eliminated artifacts like something on the lander being turned on at local midnight, so when they figure it out it should be fascinating.

In more news from the future, Boston Dynamics is trolling us again. We covered the announcement early this week that they’re putting their Spot quadruped robot on sale – sort of. Turns out you need to be selected to qualify based on the application you have in mind, plus have several Ferraris full of cash to spend. While everyone was watching the adorable antics of Spot as it wandered through improbably industrial vignettes, Boston Dynamics also released this slightly terrifying video of their Atlas robot running through a gymnastics routine.  It starts with a headstand and a front roll and ends with a slipt leap and whatever the gymnastics equivalent of a figure skating axel jump is. Yes, it has a special roll cage attached to make the tumbles a bit smoother, but it’s still some remarkable stuff.

How are your RF design skills? If they’re good enough to design an RF power amp, you might want to check out this homebrew RF design challenge. Put on by NXP Semiconductors, the design must use one of their new LDMOS RF power transistors. They’ll send you samples so you can build your design, and you stand to win up to $3000 plus $1000 worth of NXP products. The contest opened back in May but is running through the middle of November, so you’d better hurry.

Speaking of RF, wouldn’t it be interesting to see a snapshot of the RF spectrum over the entire planet? ElectroSense thinks so, and they’re working on a crowdsourcing model to set up a globe-spanning network of connected RF sensors. The idea is similar to what FlightAware does for monitoring the locations of aircraft with a distributed network of ADS-B receivers. But where FlightAware only monitors a narrow slice of spectrum, ElectroSense wants it all – DC to 6 GHz. You can build a sensor from an SDR and a Raspberry Pi and start contributing to the effort, which only has a handful of sensors at the moment.

Has affordable metal 3D-printing finally arrived? For certain values of affordability, it soon will, when One Click Metal launches their new selective laser melting printer. Thomas Sanladerer did a video with the principals, and the prototype looks promising. SLM is not a new process, but patents on the core process recently ran out, so startups like One Click Metal are jumping into the market. Their printer won’t be cheap — you’ll still need to write a check with many zeroes — but with more players, the price should come down.

And finally, what’s this world coming to when a startup specializing in building giant fighting robots can’t make a go of it? MegaBots is shutting down, and while that’s certainly bad news for its founders and employees, it’s great news for anyone in the market for used battle bots. The company’s flagship bot, the 15-ton Eagle Prime, is currently up for auction on eBay. Bidding started at $1 with no reserve, but if you were looking for a steal, you’re a bit late. The high bid is currently $100,100, which is still an incredible buy considering it cost $2.5 million to build. You’ll have to pay for shipping, but you’ll have a super-destructive mecha of your own to drive around. And think how cool you’ll look rolling into some kid’s backyard birthday party. Presumably one you’ve been invited to.