Using AI To Pull Call Signs From SDR-Processed Signals

October 9, 2018 by Steven Dufresne 8 Comments

AI is currently popular, so [Chirs Lam] figured he’d stimulate some interest in amateur radio by using it to pull call signs from radio signals processed using SDR. As you’ll see, the AI did just okay so [Chris] augmented it with an algorithm invented for gene sequencing.

His experiment was simple enough. He picked up a Baofeng handheld radio transceiver to transmit messages containing a call sign and some speech. He then used a 0.5 meter antenna to receive it and a little connecting hardware and a NooElec SDR dongle to get it into his laptop. There he used SDRSharp to process the messages and output a WAV file. He then passed that on to the AI, Google’s Cloud Speech-to-Text service, to convert it to text.

Despite speaking his words one at a time and making an effort to pronounce them clearly, the result wasn’t great. In his example, only the first two words of the call sign and actual message were correct. Perhaps if the AI had been trained on actual off-air conversations with background noise, it would have been done better. It’s not quite the same issue, but we’re reminded of those MIT researchers who fooled Google’s Inception image recognizer into thinking that a turtle was a gun.

Rather than train his own AI, [Chris’s] clever solution was to turn to the Smith-Waterman algorithm. This is the same algorithm used for finding similar nucleic acid sequences when analyzing genes. It allowed him to use a list of correct call signs to find the best match for what the AI did come up with. As you can see in the video below, it got the call signs right.

Continue reading “Using AI To Pull Call Signs From SDR-Processed Signals” →

The Return Of RadioShack?

July 23, 2018 by Dan Maloney 119 Comments

We’ve been following the ups and downs of Radio Shack for a while now, and it looks like another chapter is about to be penned in the storied retailer’s biography – and not Chapter 11 bankruptcy this time.

According to the ARRL website and major media reports, up to 50 of the 147 US locations of HobbyTown, the brick-and-mortar retailer of RC and other hobby supplies, will soon host a “RadioShack Express” outlet. Each outlet will be up to 500 square feet of retail space devoted to electronic components that would be of use to HobbyTown’s core customer base, as well as other merchandise and services.

HobbyTown locations in Mooresville, North Carolina, and Ontario, Ohio, will be among the first stores to get the RadioShack Express treatment. Current employees of the franchisees will staff the store-within-a-store, which will be stocked with RadioShack merchandise purchased by the store. Stores with Express outlets will have special RadioShack branding inside and out to attract customers. There’s talk of the deal being extended chain-wide if the pilot program goes well.

Back from the Ashes?

This is obviously great news for the beleaguered electronics retailer that was once a neighborhood fixture. True, its parts selection was often less than complete, more so in recent years than in the chain’s heyday in the mid-1970s and early 1980s. And it’s true that prices were often astronomical compared to buying online. But on a Sunday afternoon, The Shack was a lifesaver for that last minute part needed to finish a project, and the premium was well worth the convenience. Watching the decline of the chain and seeing stores disappear one by one was a slow, sad process, so that makes this seems like an unqualified positive development.

But is it? On the face of it, there’s a lot of synergy between the HobbyTown offerings and what could be stocked in a RadioShack Express. I’ve never actually visited a HobbyTown myself — I plan to fix that now that I know I’ve got an outlet nearby, even if it doesn’t appear to be on the list of 50 early Express locations — so I can only go by what I see listed online for merchandise. But a store that sells every conceivable part for RC cars and planes, drones, model rockets, and STEM-related toys and kits seems a likely place to find customers for RadioShack’s offerings.

It won’t be clear until someone sees one of these Express kiosks first hand and reports back, but it seems like we might see something like the old “cabinet o’ components” that was found in the back of the most recent incarnation of RadioShack retail stores, along with a few shelves full of things like solder, wire, and tools. There may also be some items in the Arduino-Pi space, which would be really exciting, although that might run afoul of existing HobbyTown offerings. Still, one-stop shopping of everything from servos to MOSFETs would be a huge win for electronics hobbyists.

Not the Cell Phones Again!

But there may be cause for concern. Reports are that RadioShack Express locations will also offer services such as cell phone repairs. Dipping a toe into the cell phone market seemed to be the beginning of the end for RadioShack the first time through, and by the time it was clear to everyone that the chain was on death’s door, it was hard to go into a RadioShack store without being bombarded by cell phone sales pitches. To be brutally frank, I don’t take the early inclusion of cell phone repairs as an encouraging sign of the long-term viability of the RadioShack Express concept. Do we really need another place that fixes cell phones? The areas that HobbyTown stores tend to locate are rife with places that fix phones already, so I just don’t see the point. And it just smacks of the bad old days of RadioShack.

Still, I’m cautiously optimistic that this is a positive development for RadioShack, and I think it’s a win for electronics hobbyists overall. I’ll be keeping my eye on my local HobbyTown for the return of that iconic RadioShack logo, and looking forward to the day that I can pay a buck for a resistor again. Until then, if any readers happen to be near one of the combined locations when they open next week, we’d love a boots-on-the-ground report. Post your observations in the comments below, and pix or it didn’t happen.

[via r/amateurradio]

A Guide To Audio Amps For Radio Builders

June 11, 2018 by Dan Maloney 14 Comments

For hams who build their own radios, mastering the black art of radio frequency electronics is a necessary first step to getting on the air. But if voice transmissions are a goal, some level of mastery of the audio frequency side of the equation is needed as well. If your signal is clipped and distorted, the ham on the other side will have trouble hearing you, and if your receive audio is poor, good luck digging a weak signal out of the weeds.

Hams often give short shrift to the audio in their homebrew transceivers, and [Vasily Ivanenko] wants to change that with this comprehensive guide to audio amplifiers for the ham. He knows whereof he speaks; one of his other hobbies is jazz guitar and amplifiers, and it really shows in the variety of amps he discusses and the theory behind them. He describes a number of amps that perform well and are easy to build. Most of them are based on discrete transistors — many, many transistors — but he does provide some op amp designs and even a design for the venerable LM386, which he generally decries as the easy way out unless it’s optimized. He also goes into a great deal of detail on building AF oscillators and good filters with low harmonics for testing amps. We especially like the tip about using the FFT function of an oscilloscope and a signal generator to estimate total harmonic distortion.

The whole article is really worth a read, and applying some of these tips will help everyone do a better job designing audio amps, not just the hams. And if building amps from discrete transistors has you baffled, start with the basics: [Jenny]’s excellent Biasing That Transistor series.

[via Dangerous Prototypes]

Raspberry Pi Is Up Up And Away

May 2, 2018 by Al Williams 3 Comments

BACAR — Balloon Carrying Amateur Radio — is just what it sounds like. A high-altitude balloon carries experiments and communicates via amateur radio. [ZR6AIC] decided to fly a payload in a local BACAR experiment. The module would send its GPS position via the APRS network and also send a Morse code beacon every seven minutes. It also sends other data such as temperature, and has an optional camera fitted.

The hardware used was the ubiquitous Raspberry Pi along with an associated daughterboard for transmitting on the 2 meter ham band. An RTL dongle took care of the receive portion and another dongle provided GPS. A DS18B20 temperature sensor provides the temperature data.

Continue reading “Raspberry Pi Is Up Up And Away” →

Temperature Sensor And Simple Oscillator Make A Value-Added HF Beacon

April 24, 2018 by Dan Maloney 13 Comments

Sometimes the best projects are the simple, quick hits. Easily designed, fast to build, and bonus points for working right the first time. Such projects very often lead to bigger and better things, which appears to be where this low-power temperature beacon is heading.

In the world of ham radio, beacon stations are transmitters that generally operate unattended from a known location, usually at limited power (QRP). Intended for use by other hams to determine propagation conditions, most beacons just transmit the operator’s call sign, sometimes at varying power levels. Any ham that can receive the signal will know there’s a propagation path between the beacon and the receiver, which helps in making contacts. The beacon that [Dave Richards (AA7EE)] built is not a ham beacon, at least not yet; operating at 13.56 MHz, it takes advantage of FCC Part 15 regulations regarding low-power transmissions rather than the Part 97 rules for amateur radio. The circuit is very simple — a one-transistor Colpitts oscillator with no power amplifier, and thus very limited range. But as an added twist, the oscillator is keyed by an ATtiny13 hooked to an LM335 temperature sensor, sending out the Celsius and Fahrenheit temperature in Morse every 30 seconds or so. The circuit is executed in Manhattan style, which looks great and leaves plenty of room for expansion. [Dave] mentions adding a power amp and a low-pass filter to get rid of harmonics and make it legal in the ham bands.

Beacons are just one of the ways for hams to get on the air without talking. Another fun way to analyze propagation is WSPR, which is little like an IoT beacon.

Continue reading “Temperature Sensor And Simple Oscillator Make A Value-Added HF Beacon” →

An SSB Transceiver On Only One Type Of Transistor

April 9, 2018 by Jenny List 31 Comments

There are a multiplicity of transmission modes both new and old at the disposal of a radio amateur, but the leader of the pack is still single-sideband or SSB. An SSB transmitter emits the barest minimum of RF spectrum required to reconstitute an audio signal, only half of the mixer product between the audio and the RF carrier, and with the carrier removed. This makes SSB the most efficient of the analog voice modes, but at the expense of a complex piece of circuitry to generate it by analog means. Nevertheless, radio amateurs have produced some elegant designs for SSB transmitters, and this one for the 80m band from [VK3AJG] is a rather nice example even if it isn’t up-to-the-minute. What makes it rather special is that it relies on only one type of device, every one of its transistors is a BC547.

In design terms, it follows the lead set by other simple amateur transmitters, in that it has a 6 MHz crystal filter with a mixer at either end of it that switch roles on transmit or receive. It doesn’t use the bidirectional amplifiers popularised by VU2ESE’s Bitx design, instead, it selects transmit or receive using a set of diode switches. The power amplifier stretches the single-device ethos to the limit, by having multiple BC547s in parallel to deliver about half a watt.

While this transmitter specifies BC547s, it’s fair to say that many other devices could be substituted for this rather aged one. Radio amateurs have a tendency to stick with what they know and cling to obsolete devices, but within the appropriate specs a given bipolar transistor is very similar to any other bipolar transistor. Whatever device you use though, this design is simple enough that you don’t need to be a genius to build one.

Via [G4USP]. Thanks [2ftg] for the tip.

Simple Decoder Serves As Solo Ham’s Test Buddy

March 31, 2018 by Dan Maloney 11 Comments

For a hobby that’s ostensibly all about reaching out to touch someone, ham radio can often be a lonely activity. Lots of hams build and experiment with radio gear much more than they’re actually on the air, improving their equipment iteratively. The build-test-tweak-repeat cycle can get a little tedious, though, especially when you’re trying to assess signal strength and range and can’t find anyone to give you a report.

To close the loop on field testing, [WhiskeyTangoHotel] threw together a simple ham radio field confirmation unit that’s pretty slick. It relies on the fact that almost every ham radio designed for field use incorporates a DTMF encoder in the microphone or in the transceiver itself. Hams have used Touch Tones for in-band signaling control of their repeaters for decades, and even as newer digital control methods have been introduced, good old analog DTMF hangs in there. The device consists of a DTMF decoder attached to the headphone jack of a cheap handy talkie. When a DTMF tone is received, a NodeMCU connected to the decoder calls an IFTTT job to echo the key to [WTH]’s phone as an SMS message. That makes it easy to drive around and test whether his mobile rig is getting out. And since the receiver side is so portable, there’s a lot of flexibility in how tests can be arranged.

On the fence about ham as a hobby? We don’t blame you. But fun projects like this are the perfect excuse to go get licensed and start experimenting.

Continue reading “Simple Decoder Serves As Solo Ham’s Test Buddy” →