Finding Noise With An Antenna

March 1, 2018 by Kristina Panos 3 Comments

[K5ACL], aka [SignalSearch], recently brought his active receive loop antenna in off the roof to give it a checkup and perform any necessary maintenance. While it was in the shack, he took the opportunity to discuss how well it would perform indoors. The verdict? Not ideal. He’d mount it 50 feet away from the house if the HOA would let him.

Houses, and subsequently most ham shacks, are filled with noise sources that interfere badly with HF. So after spending a minute or so listening on an SDR, [K5ACL] demonstrates another use for this type of tightly-tuned antenna—as a noise detector.

The main culprit in [K5ACL]’s house is the ceiling light that’s right there in the shack. You can see the noise striping the waterfall as he turns it on and off. But the noise from the light is small potatoes compared to some other common household items, like those power line adapters that turn house wiring into networking cable. Those produce so much noise that even an active loop is really no match. Stay tuned after the break to watch [K5ACL] work the bands through the noise.

Loop antennas are great if you’re stuck in an apartment building or a congested city. They’re easy enough to make, whether you want a portable loop or a permanent installation.

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Quantifying Latency In Cheap RC Transmitters

February 26, 2018 by Tom Nardi 58 Comments

For those just starting out in the world of RC, a low cost transmitter like the Flysky FS-i6S can be very compelling. But is buying a cheap transmitter setting yourself up for failure down the line? The general feel in the RC community has been that cheaper transmitters have higher latency or “lag” on their inputs, which is precisely the kind of thing you want to avoid when flying along at 40+ MPH. As such, the general wisdom has been that your transmitter is one area where you don’t want to cheap out.

Wanting to put that theory to the test, [Marek Baczynski] set out to compare the response time between the Flysky FS-i6S and the more established Taranis X9D. In the video after the break, he uses his Saleae logic analyzer to time how long it takes movement on the transmitter sticks to get interpreted as servo commands at the receiver.

[Marek] connects the logic analyzer directly to the gimbals of both transmitters, allowing him to see user input before any processing is done by the electronics. It’s particularly interesting to see how the smooth analog curves of the gimbals are converted to a “staircase” digital output.

The final results of the latency test end up being fairly surprising. To put it simply: the cheaper Flysky radio not only more accurately interprets the user’s input, but does it considerably faster than the Taranis. [Marek] says he was so surprised by these results that he re-ran the test three times to verify.

But even taking into account the apparently higher fidelity of the cheap radio, he cautions you shouldn’t swap out your gear just yet. Higher end transmitters have a number of other features which make them worth hanging on to, even if the newer generation of radios is slightly faster. The real takeaway from this video is that if you’re just getting into the RC game, these cheaper transmitters aren’t necessarily the kiss of death the community makes them out to be.

Experiments like this and the recent detailed analysis of common hobby motors show just how seriously people take the world of RC. It’s unlikely this single experiment will quell the debate about “cheap” RC transmitters, but perhaps it’s a start.

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This Radio Gets Pour Reception

February 22, 2018 by James Hobson 17 Comments

When was the last time you poured water onto your radio to turn it on?

Designed collaboratively by [Tore Knudsen], [Simone Okholm Hansen] and [Victor Permild], Pour Reception seeks to challenge what constitutes an interface, and how elements of play can create a new experience for a relatively everyday object.

Lacking buttons or knobs of any kind, Pour Reception appears an inert acrylic box with two glasses resting on top. A detachable instruction card cues the need for water, and pouring some into the glasses wakes the radio.

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At 71,572 KM, You Won’t Beat This LoRa Record

February 22, 2018 by Jenny List 29 Comments

A distance record for LoRa transmission has been set that you probably won’t be able to beat. Pack up your gear and go home, nothing more to achieve here. At a superficial reading having a figure of 71,572 km (44,473 miles) seems an impossible figure for one of the little LoRa radio modules many of us have hooked up to our microcontrollers, but the story isn’t quite what you’d expect and contains within it some extremely interesting use of technology.

So the folks at Outernet have sent data over LoRa for that incredible distance, but they did so not through the little ISM band modules we’re used to but over a suitably powerful Ku-band uplink to a geostationary satellite. They are also not using the LoRaWAN protocols of the earthbound systems, but simply the LoRa modulation scheme. So it’s not directly comparable to terrestrial records such as the 702 km we reported on last year, and they are the first to admit that.

Where their achievement becomes especially interesting though is in their choice of receiver. We are all used to Ku-band receivers, you may even have one on your house somewhere for satellite TV. It will probably involve a parabolic dish with a narrow beam width and an LNB whose horn antenna is placed at its focus. It would have required some skill and effort to set up, because it has to be pointed very carefully at the satellite’s position in the sky. Outernet’s mission of delivering an information service with the lowest possible barrier to entry precludes the extra expense of shipping a dish and providing trained staff to align it, so they take a very different approach. Their receiver uses either an LNB horn or a small patch antenna pointing at the satellite, with none of the dishes or phased arrays you might be used to in a Ku-band installation.

You might wonder how such a receiver could possibly work with such a meagre antenna, but the secret lies in LoRa’s relatively tiny bandwidth as well as the resistance to co-channel interference that is a built-in feature of the LoRa modulation scheme. Even though the receiver will be illuminated by multiple satellites at once it is able to retrieve the signal and achieve a 30 kb/s data rate that they hope with technical refinements to increase to 100 kb/s. This rate will be enough over which to push an SD video stream to name just one of the several examples of the type of content they hope to deliver.

It’s likely that the average Hackaday reader will not be hiring satellite uplink time upon which to place their LoRa traffic. But this story does provide a demonstration of LoRa’s impressive capabilities, and will make us look upon our humble LNBs with new eyes.

Via ABOpen.

An Especially Tiny And Perfectly Formed FM Bug

February 21, 2018 by Jenny List 17 Comments

It used to be something of an electronic rite of passage, the construction of an FM bug. Many of us will have taken a single RF transistor and a tiny coil of stiff wire, and with the help of a few passive components made an oscillator somewhere in the FM broadcast band. Connect up a microphone and you were a broadcaster, a prankster, and probably set upon a course towards a life in electronics. Back in the day such a bug might have been made from components robbed from a piece of scrap consumer gear such as a TV or VCR, and perhaps constructed spider-web style on a bit of tinplate. It wouldn’t have been stable and it certainly wouldn’t have been legal in many countries but the sense of achievement was huge.

As you might expect with a few decades of technological advancement, the science of FM bugs has moved with the times. Though you can still buy the single transistor bugs as kits there is a whole range of fancy chips designed for MP3 players that provide stable miniature transmitters with useful features such as stereo encoders. That’s not to say there isn’t scope for an updated simple bug too though, and here [James] delivers the goods with his tiny FM transmitter.

Gone is the transistor, and in its place is a MAX2606 voltage-controlled oscillator. The on-chip varicap and buffer provided by this device alleviate some of the stability issues suffered by the transistor circuits, and to improve performance further he’s added an AP2210 low-dropout regulator to catch any power-related drift. If it were ours we’d put in some kind of output network to use both sides of the differential output, but his single-ended solution at least offers simplicity. The whole is put on a board so tiny as to be dwarfed by a CR2032 cell, and we can see that a bug that size could provide hours of fun.

This may be a small and simple project, but it has found its way here for being an extremely well-executed one. It’s by no means the first FM bug we’ve shown you here, just a few are this one using scavenged SMD cellphone parts, or this more traditional circuit built on a piece of stripboard.

AI Listens To Radio

February 17, 2018 by Al Williams 5 Comments

We’ve seen plenty of examples of neural networks listening to speech, reading characters, or identifying images. KickView had a different idea. They wanted to learn to recognize radio signals. Not just any radio signals, but Orthogonal Frequency Division Multiplexing (OFDM) waveforms.

OFDM is a modulation method used by WiFi, cable systems, and many other systems. In particular, they look at an 802.11g signal with a bandwidth of 20 MHz. The question is given a receiver for 802.11g, how can you reliably detect that an 802.11ac signal — up to 160 MHz — is using your channel? To demonstrate the technique they decided to detect 20 MHz signals using a 5 MHz bandwidth.

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This IS Your Grandfather’s Radio

February 14, 2018 by Al Williams 9 Comments

Tube radios have a certain charm. Waiting for them to warm up, that glow of the filaments in a dark room. Tubes ruled radio for many decades. [Uniservo] posted a video about the history and technology behind the 1920’s era Clapp-Eastham C-3 radio. This is a three-tube regenerative receiver and was advanced for its day.

If you are worried he won’t open it up, don’t despair. Around the ten minute mark, your patience will be rewarded. Inside are three big tubes full of getter and bus bars instead of wires. Add to that the furniture-quality case, and this is a grand old radio.

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