LoRa Is The Network

October 24, 2017 by Jenny List 29 Comments

We’ve become used to seeing LoRa appearing in projects on these pages, doing its job as a low-bandwidth wireless data link with a significant range. Usually these LoRa projects take the form of a client that talks to a central Internet connected node, allowing a remote wireless-connected device to connect through that node to the Internet.

It’s interesting then to see a modest application from [Mark C], a chat application designed to use a set of LoRa nodes as a peer-to-peer network. In effect LoRa becomes the network, instead of simply being a tool to access it. He optimistically describes peer-to-peer LoRa networks as the new FidoNet in his tip email to us, which might be a bold statement, but we can certainly see some parallel. It’s important to note that the application is merely a demonstrable proof-of-concept as it stands, however we’d agree that it has some potential.

The hardware used for the project is the Heltec ESP32-based LoRa board, which comes with a handy OLED screen on which the messages appear. As it stands a PC connection is required to provide text input via serial, however it’s not impossible to imagine other more stand-alone interfaces. If it interests you the code can be downloaded from the GitHub repository, so maybe this can become the seed for wider peer-to-peer LoRa networks.

There have been no shortage of LoRa projects featured here over the years. Recent ones include a handy local LoRa packet sniffer, and news of an extreme distance record from a LoRa node on a balloon.

3D Printed Dashboard CB Mount Is Convoy Ready

October 21, 2017 by Tom Nardi 12 Comments

Some may be surprised to hear that CB radio is alive and well in the 21st century. From disaster response to operating in areas without reliable communication infrastructure, there are plenty of reasons people are still reaching for their radio and not their smartphone. Unfortunately, modern automotive interior design doesn’t have such an enlightened view. It’s hard enough to get decent cup holders in some cars, let alone a spot to hang your microphone.

When presented with this problem in his Subaru Forester, [Alex Loizou] did what any modern hacker would, he 3D printed a mount that snaps into the stock dash. No drilling was required to attach his radio mount, it simply replaces a decorative trim piece that wasn’t doing anything anyway. Obviously this particular mount would only really work on the same year and make of vehicle as [Alex] has, but this is a good demonstration of how 3D printing can be used to adapt to existing hardware.

As is often the case when trying to print something to match perfectly with an existing object, there was a fair amount of trial and error required. It took a few attempts before [Alex] got the proper shape, and things weren’t made any easier by the fact he was doing his designing in TinkerCAD. While we appreciate the fact that TinkerCAD provides a web-based CAD tool that is easy enough for anyone to use, using a parametric design tool like OpenSCAD is generally preferred when you need to make slight adjustments to your model.

Software limitations aside, [Alex] managed to come up with a mount that not only holds his CB microphone, but also his handheld transmitter. All while looking about as close to stock hardware as something like this could. We especially like that he switched to a darker filament color for his final version to blend it into the dashes color scheme a bit better.

If your radio interest is a little full-fat for CB, take a look at what keeps ham radio alive and well in 2017, and if you’re a radio amateur with a hankering for the CB days we’ve got you covered.

Snazzy Balun Lets Ham Use Off-The-Shelf Coax

October 16, 2017 by Dan Maloney 42 Comments

It’s a dilemma many hams face: it’s easy to find yourself with a big spool of RG-11 coax cable, usually after a big cable TV wiring project. It can be tempting to use it in antenna projects, but the characteristic impedance of RG-11 is 75 Ω, whereas the ham world is geared to 50 Ω. Not willing to waste a bounty of free coax, one ham built a custom 1:1 current balun for a 75 Ω dipole.

Converting between balanced and unbalanced signals is the job of a balun, and it’s where the device derives its name. For hams, baluns are particularly useful to connect a dipole antenna, which is naturally balanced, to an unbalanced coax feedline. The balun [NV2K] built is a bifilar 1:1 design, with two parallel wires wound onto a ferrite core. To tweak the characteristic impedance to the 75 Ω needed for his antenna and feedline, [NV2K] added short lengths of Teflon insulation to one of the conductors, which is as fussy a bit of work as we’ve seen in a while. We appreciate the careful winding of the choke and the care taken to make this both mechanically and electrically sound, and not letting that RG-11 go to waste is a plus.

With as much effort as hams put into antenna design, there’s a surprising dearth of Hackaday articles on the subject. We’ve talked a bit about the Yagi-Uda antenna, and we’ve showcased a cool magnetic loop antenna, but there’s precious little about the humble dipole.

[via r/amateurradio]

The Early Bird Repairs A Slug

October 13, 2017 by Adam Fabio 12 Comments

When faced with a problematic Bird slug, [Robert Meister] didn’t give up. He pecked away at the slug and brought us all along for the ride. If that sentence didn’t make sense to you, read on!

Anyone who’s been to a hamfest has seen a Bird meter. The Bird Model 43 watt meter is the defacto standard for measuring transmitter power in-line. Bird meters don’t just work from DC to light though. In fact, the model 43 itself is just a bit of transmission line and a meter movement. The magic happens inside the swappable measurement element. These elements, affectionately called “slugs” are calibrated for a frequency band and power range. An example would be the model 4410-6, which works from 50 – 200 MHz, at up to 1 kW. Most hams have a collection of these slugs to go with the bands they transmit on.

[Robert]’s problem child was a model 100E element, good for 100 watts on 400 – 1000 MHz. The meter output seemed erratic though. A bit of troubleshooting with a second meter and a known good slug isolated the problem to the 100E. The problem was isolated to the slug, but how to fix it?

Slugs are sealed brass containers, each of which is calibrated to 5% accuracy at the factory. They are the closest thing you’ll find in the ham world to “no user serviceable parts inside”. Still, [Robert] had nothing to lose. He soaked the slug in a bit of Xylene solvent to loosen the glue holding the metal label on. Behind that were a painted screw and a hole for a calibration pot. We’re guessing the paint is Bird’s idea of tamper detection.

Pulling the screw out, and removing the nylon cover on the back of the slug revealed the real story. The slug contained a calibrated sensing loop, a diode, the calibration pot, and a terminating resistor. In [Robert]’s case, all he had to do was clean the contacts on the slug, and things worked fine.

For 11 years, anyway. After that, the slug started acting up again. Cleaning didn’t fix the problem this time. [Robert] ended up replacing the calibration potentiometer with a similar model from Digi-key. He re-calibrated the slug against his known good meter. It may not be a lab quality calibration, but this slug should be good for another few decades in his shack.

Retrotechtacular: Radio To Listen To When You Duck And Cover

October 12, 2017 by Al Williams 34 Comments

CONELRAD may sound like the name of a fictional android, but it is actually an acronym for control of electronic radiation. This was a system put in place by the United States at the height of the cold war (from 1951 to 1963) with two purposes: One was to disseminate civil defense information to the population and, also, to eliminate radio signals as homing beacons for enemy pilots.

Continue reading “Retrotechtacular: Radio To Listen To When You Duck And Cover” →

Homemade 6 GHz Radar, V3

October 11, 2017 by Pedro Umbelino 28 Comments

The third version of [Henrik Forstén] 6 GHz frequency-modulated continuous wave (FMCW) radar is online and looks pretty awesome. A FMCW radar is a type of radar that works by transmitting a chirp which frequency changes linearly with time. Simple continuous wave (CW) radar devices without frequency modulation cannot determine target range because they lack the timing mark necessary for accurately time the transmit and receive cycle in order to convert this information to range. Having a transmission signal modulated in frequency allows for the radar to have both a very high accuracy of range and also to measure simultaneously the target range and its relative velocity.

Like the previous versions, [Henrik] designed a four-layer pcb board and used his own reflow oven to solder all the ~350 components. This process, by itself, is a huge accomplishment. The board, much bigger than the previous versions, now include digital signal processing via FPGA.

[Henrik’s] radar odyssey actually started back in 2014, where his first version of the radar was detailed and shared in his blog. A year later he managed to solve some of the issues he had, design a new board with significant improvements and published it again. As the very impressive version three is out, we wonder what version four will look like.

In the video of [Henrik] riding a bicycle in a circle in front of the radar, we can see the static light posts and trees while he, seen as a small blob, roams around:

Continue reading “Homemade 6 GHz Radar, V3” →

One Man’s Tale Of EMC Compliance Testing

October 9, 2017 by Jenny List 31 Comments

If you turn over almost any electronic device, you should find all those compliance logos: CE, FCC, UL, TÜV, and friends. They mean that the device meets required standards set by a particular region or testing organisation, and is safe for you, the consumer.

Among those standards are those concerning EMC, or ElectroMagnetic Compatibility. These ensure that the device neither emits RF radiation such that it might interfere with anything in its surroundings, nor is it unusually susceptible to radiation from those surroundings. Achieving a pass in those tests is something of a black art, and it’s one that [Pero] has detailed his exposure to in the process of seeing a large 3-phase power supply through them. It’s a lengthy, and fascinating post.

He takes us through a basic though slightly redacted look at the device itself, before describing the testing process, and the EMC lab. These are fascinating places with expert staff who can really help, though they are extremely expensive to book time in. Since the test involves a mains power supply he describes the Line Impedance Stabilisation Network, or LISN, whose job is to safely filter away the RF component on the mains cable, and present a uniform impedance to the device.

In the end his device failed its test, and he was only able to achieve a pass with a bit of that black magic involving the RF compliance engineer’s secret weapons: copper tape and ferrite rings. [Pero] and his colleagues are going to have to redesign their shielding.

We’ve covered our visits to the EMC test lab here before.