There was a time when the measure of a transmitting radio antenna was having it light an incandescent bulb. A step up was a classic SWR/Power meter that showed you forward and reflected power. Over the years, a few other instruments have tried to provide a deeper look into antenna performance. However, the modern champion is the antenna analyzer which is a way of measuring vector impedance.
[Captain Science] did a review of an inexpensive N1201SA analyzer. This device is well under $200 from the usual Chinese sellers. The only thing a bit odd is the frequency range which is 140 MHz to 2700 MHz. For some extra money (about $80 or $100 more) you can drop the low-end frequency to just under 35 MHz.
Continue reading “Antenna Analyzer is a Lab in a Box”
With almost 8 billion souls to feed and a changing climate to deal with, there’s never been a better time to field a meaningful “Internet of Agriculture.” But the expansive fields that make industrial-scale agriculture feasible work against the deployment of sensors and actuators because of a lack of infrastructure to power and connect everything. So a low-power radio network for soil moisture sensors is certainly a welcome development.
We can think of a lot of ways that sensors could be powered in the field. Solar comes to mind, since good exposure to the sun is usually a prerequisite for any cropland. But in practice, solar has issues, the prime one being that the plants need the sun more, and will quickly shade out low-profile soil-based sensors.
That’s why [Spyros Daskalakis] eschewed PV for his capacitive soil moisture sensors in favor of a backscatter technique very similar to that used in both the Great Seal Bug and mundane RFID tags alike. The soil sensor switches half of an etched PCB bowtie antenna in and out of a circuit at a frequency proportional to soil moisture. A carrier signal from a separate transmitter is reflected off the alternately loaded and unloaded antenna, picking up subcarriers with a frequency proportional to soil moisture. [Spyros] explains more about the sensor design and his technique for handling multiple sensors in his paper.
We really like the principles [Spyros] leveraged here, and the simplicity of the system. We can’t help but wonder what sort of synergies there are between this project and the 2015 Hackaday Prize-winning Vinduino project.
Continue reading “Using Backscatter Radio for a Soil Sensor Network”
The place is the historic lecture theater of the Royal Institution in London. The date is the 4th of June 1903, and the inventor, Guglielmo Marconi, is about to demonstrate his new wireless system, which he claims can securely send messages over a long distance, without interference by tuning the signal.
The inventor himself was over 300 miles away in Cornwall, preparing to send the messages to his colleague Professor Fleming in the theater. Towards the end of Professor Flemings lecture, the receiver sparks into life, and the morse code printer started printing out one word repeatedly: “Rats”. It then spelled out an insulting limerick: “There was a young man from Italy, who diddled the public quite prettily”. Marconi’s supposedly secure system had been hacked.
Continue reading “Origin of Wireless Security: the Marconi Radio Hack of 1903”
When you get to a certain age, you get unsettled by people calling “your” music oldies. That’s how a few of us felt when we saw [Mikrowave1’s] video about Retro QRP – Solid Gold Years (see below). “QRP” is the ham radio term for low power operation, and the “solid gold” years in question are the 1960s to 1980. The videox has some good stuff, including some old books and some analysis of a popular one-transistor design from that time. He even tries a few different period transistors to see which works best.
[Mikrowave1] talks about the construction techniques used in that time frame, old transistors, and some vintage test equipment. You can even see an old ARC-5 command receiver in use to listen to the transmitter. These were made for use in military aircraft and were very common as surplus.
Continue reading “Looking Back at QRP Transmitters”
We don’t know if [OH8STN] has a military background, but we suspect he might since his recent post is about a “DIY Man Portable Magnetic Loop Antenna.” “Man-portable” is usually a military designation, and — we presume — he wouldn’t object to a woman transporting it either.
[OH8STN] started with a Chameleon antenna starter kit. This costs about $100 and is primarily a suitable variable capacitor with a 6:1 reduction drive premounted and soldered. Of course, you could source your own, but finding variable capacitors that can handle transmit duty (admittedly, these can apparently handle about 10 W continuous or 25 W on single sideband) can be tricky, especially these days. Although he started with a kit, he did modify the antenna to switch between two different sets of ham radio bands. You can see the antenna in the video below.
Loop antennas aren’t ideal–but neither is any other small antenna. Because the loop is tightly tuned to a particular frequency, it requires retuning for even relatively small frequency changes, even though it can operate on many different frequencies. If you want more technical details, you might enjoy this recent presentation from [W4RAX]. The links at the end are worth checking out, too.
Continue reading “Loop Antenna is Portable”
What’s the minimal BOM for a working amateur radio transmitter? Looks like you can get away with seven parts, or eight if you include the walnut. You’ve got to have a walnut.
Some hams really love the challenge of QRP, or the deliberate use of low-power transmitters to provide a challenge to making long-distance contacts. We’ve covered the world of QRP before and noted that while QRP rigs don’t throw a lot of power, it doesn’t mean that they need to be simple. Some get quite complex and support many different modulation schemes, even digital modes. With only a single 2N3904 transistor, [Jarno (PA3DMI)]’s tiny transmitter won’t do much more than send Morse using CW modulation, but given that it’s doing so from inside a walnut shell, we have no complaints. The two halves of the shell are hinged together and hold a scrap of perfboard for the simple quartz crystal oscillator. The prototype was tuned outside the shell, and the 9-volt battery is obviously external, but aside from that it’s nothing but nuts.
We’d love to see [Jarno] add a spring to the hinge and contacts on the shell halves so no keyer is required. Who knows? Castanet-style keying might be all the rage with hams after that.
Continue reading “Ham Goes Nuts for Tiny Transmitter”
If you are fascinated by stories you read on sites like Hackaday in which people reverse engineer wireless protocols, you may have been tempted to hook up your RTL-SDR stick and have a go for yourself. Unfortunately then you may have encountered the rather steep learning curve that comes with these activities, and been repelled by a world with far more of the 1337 about it than you possess. You give up after an evening spent in command-line dependency hell, and move on to the next thing that catches your eye.
You could then be interested by [Jopohl]’s Universal Radio Hacker. It’s a handy piece of software for investigating unknown wireless protocols. It supports a range of software defined radios including the dirt-cheap RTL-SDR sticks, quickly demodulates any signals you identify, and provides a whole suite of tools to help you extract the data they contain. And for those of you scarred by dependency hell, installation is simple, at least for this Hackaday scribe. If you own an SDR transceiver, it can even send a reply.
To prove how straightforward the package is, we put an RTL stick into a spare USB port and ran the software. A little investigation of the menus found the spectrum analyser, with which we were able to identify the 433 MHz packets coming periodically from a wireless thermometer. Running the record function allowed us to capture several packets, after which we could use the interpretation and analysis screens to look at the binary stream for each one. All in the first ten minutes after installation, which in our view makes it an easy to use piece of software. It didn’t deliver blinding insight into the content of the packets, that still needs brain power, but at least if we were reverse engineering them we wouldn’t have wasted time fighting the software.
We’ve had so many reverse engineering wireless protocol stories over the years, to pick only a couple seems to miss the bulk of the story. However both this temperature sensor and this weather station show how fiddly it can be without a handy software package to make it easy.
Via Hacker News.