Neural Network Learns SDR Ham Radio

Identifying ham radio signals used to be easy. Beeps were Morse code, voice was AM unless it sounded like Donald Duck in which case it was sideband. But there are dozens of modes in common use now including TV, digital data, digital voice, FM, and more coming on line every day. [Randaller] used CUDA to build a neural network that could interface with an RTL-SDR dongle and can classify the signals it hears. Since it is a neural network, it isn’t so much programmed to do it as it is trained. The proof of concept has training to distinguish FM, SECAM, and tetra. However, you can train it to recognize other modulation schemes if you want to invest the time into it.

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Radio Amateuring Like It’s 1975

It was a tweet from an online friend in the world of amateur radio, featuring a transmitter design published in Sprat, the journal of the G-QRP club for British enthusiasts of low-power radio. The transmitter was very simple, but seriously flawed: keying the power supply line would cause it to exhibit key clicks and frequency instability. It would probably have been far better leaving the oscillator connected full-time and keying the supply to the amplifier, with of course a suitable key click filter.

[M0CVO]'s Tweet that started it all
[M0CVO]’s Tweet that started it all
We’ve all probably made projects that get the job done at the expense of a bit of performance and economy, and from one angle this circuit is a fantastic example of that art. But it’s not the shortcomings of direct PSU keying a small transmitter that has brought it here, but observation instead of what it represents. Perhaps my social group of radio amateurs differs from the masses, but among them the universal lament is that there is nothing new in a simple transistor transmitter that could just as well have been published in 1977 as 2017.

To explain why this represents a problem, it’s worth giving some background. Any radio amateur will tell you that amateur radio is a wonderful and diverse pastime, in fact a multitude of pastimes rolled into one. Working DX? Got you covered. Contesting? UR 599 OM QRZ? Digital modes pushing the envelope of atmospheric propagation? Satellites? SDRs? GHz radio engineering? All these and many more can be yours for a modest fee and an examination pass. There was a time when radio was electronics, to all intents and purposes, and radio amateurs were at the vanguard of technology. And though electronics has moved on from those days of purely analogue communications and now stretches far beyond anything you’d need a licence and a callsign to investigate for yourself, there are still plenty of places in which an amateur can place themselves at the cutting edge. Software defined radio, for instance, or digital data transmission modes. With an inexpensive single board computer and a few components it is now possible to create a software-defined digital radio station with an extremely low power output, that can be copied on the other side of the world. That’s progress, it’s not so long ago that you would have required a lot of dollars and a lot of watts to do that. Continue reading “Radio Amateuring Like It’s 1975”

Slinky Walks Down Stairs and Picks up 80m Band

Originally intended as a way to stabilize sensitive instruments on ships during World War II, the Slinky is quite simply a helical spring with an unusually good sales pitch. But as millions of children have found out since the 1940’s, once you roll your Slinky down the stairs a few times, you’ve basically hit the wall in terms of entertainment value. So what if we told you there was yet another use for this classic toy that was also fun for a girl and a boy?

As it turns out, a cheap expandable metal coil just so happens to make for a pretty good antenna if you hook it up right. [Blake Hughes] recently took on this project and provided some detailed pictures and information for anyone else looking to hook a couple of Slinkies to their radio. [Blake] reports excellent results when paired to his RTL-SDR setup, but of course this will work with whatever kind of gear you might be using at these frequencies.

Before anyone gets out the pitchforks, admittedly this isn’t exactly a new idea. There are a few other write-ups online about people using a Slinky as a cheap antenna, such as this detailed analysis from a few years ago by [Frank Dörenberg]. There’s even rumors that soldiers used a Slinky from back home as a makeshift antenna during the Vietnam War. So this is something of an old school ham trick revived for the new generation of SDR enthusiasts.

Anyway, the setup is pretty simple. You simply solder the RF jack of your choice to two stretched out Slinkies: one to the center of the jack and one to outside. Then run a rope through them and stretch them out in opposite directions. The rope is required because the Slinky isn’t going to be strong enough when expanded to keep from laying on the ground.

One thing to keep in mind with a Slinky antenna is that these things are not exactly rated for outside use. Without some kind of treatment (like a spray on acrylic lacquer) , they’ll quickly corrode and fail. Though a better idea might simply to be to think of this as a temporary antenna that you put away when you’re done with. Thanks to the fact that the Slinky doesn’t get deformed even when stretching it out to maximum length, that’s relatively easy to accomplish.

If you’re looking for a good RTL-SDR to go along with your new Slinky antenna, check out this roundup of some of the options that are on the market as of 2017. You’ll probably need an upconverter to get down to the 80m band, so you might as well build that while you’re at it.

AMSAT MPPT Goes to Infinity and Beyond

AMSAT, the Radio Amateur Satellite Corporation, joined forces with students from Rochester Institute of Technology to create a MPPT attached to a Fox-1B CubeSat. It successfully launched into orbit on November 18th strapped to the back of a Delta II rocket. This analog MPPT, or Maximum Power Point Tracker, is used for optimizing the draw of a power cell in correspondence to the output of solar panels on the 10cm x 10cm satellite. In a nutshell, this works by matching the voltage of the two together. If you haven’t gotten a chance to play around with one of these first hand, Hackaday’s own [Elliot Williams] wrote up a thorough explanation of the glorious MPPT’s efficiency.

This little guy is currently hurtling along in an orbit every 90 minutes. During each of these elliptical trajectories, the satellite undergoes brutal heating and cooling cycles. The team calculated that this package will undergo a total of 29,200 orbits around Earth during its 5 year mission. This means that there are 29,200 tests for it to crack — quite literally — under pressure. To add another level of difficulty, the undergrad team didn’t have funding for automated board assembly. This meant that they had to hand solder over 400 micro components onto this board, adding additional human error to be accounted for in the likelihood of a failure. But so far, this puppy is going strong. This truly shows the struggles that can be overcome with a little elbow grease, hard work, and plain ‘ole good engineering.

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Raspberry Pi Learns Slow Morse Code

It wasn’t long ago that you needed to know Morse code to be a ham radio operator. That requirement has gone in most places, but code is still useful and many hams use it, especially hams that like to hack. Now, hams are using the Raspberry Pi to receive highly readable Morse code using very low power. The software is QrssPiG and it can process audio or use a cheap SDR dongle.

There are a few reasons code performs better than voice and many other modes. First, building transmitters for Morse is very simple. In addition, Morse code is highly readable, even under poor conditions. This is partly because it is extremely narrow bandwidth and partly because your brain is an amazing signal processor.

Like most communication methods, the slower you go the easier it is to get a signal through. In ham radio parlance, QRS means “send slower”, so QRSS has come to mean mean “send very slowly”. So hams are using very slow code, and listening for it using computerized methods. Because the data rate is so slow, the computer has time to do extreme methods to recover the signal — essentially, it can employ an extremely narrow filter. Having a QRSS signal detected around the world from a transmitter running much less than a watt is quite common. You can see a video introduction to the mode from [K6BFA] and [KI4WKZ], below.

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Satellite Tracking With Friends

If you’re in the mood to track satellites, it’s a relatively simple task to look up one of a multitude of websites that can give you a list of satellites visible from your location. However, if you’re interested in using satellites to communicate with far-flung friends, you might be interested in this multi-point satellite tracker.

[Stephen Downward VA1QLE] developed the tracker to make it easier to figure out which satellites would be simultaneously visible to people at different locations on the Earth’s surface. This is useful for amateur radio, as signals can be passed through satellites with ham gear onboard (such as NO-44), or users can even chat over defunct military satellites.

[Stephen] claims the algorithm is inefficient, but calculations are made in a matter of a few seconds, so we’re not complaining. While it was originally designed for just two stations, it works with a near-infinite number of points. [Stephen] recommends verifying the tracks with another tool once calculated to ensure accuracy. The tool is accessible here, and the code is up on GitHub for your perusal.

Perhaps now you need a cost-effective satellite-tracking antenna? [Paul] has you covered.

A Ham Radio Go-Box Packed with Functionality

“When all else fails, there’s ham radio.” With Hurricane Harvey just wrapping up, and Irma queued up to clobber Florida this weekend, hams are gearing up to pitch in with disaster communications for areas that won’t have any communications infrastructure left. And the perfect thing for the ham on the go is this ham shack in a box.

Go-boxes, as they are known, have been a staple of amateur radio field operations for as long as there have been hams. The go-box that [Fuzz (KC3JGB)] came up with is absolutely packed with goodies that would make it a perfect EmComm platform. The video tour below is all we have to go on, but we can see a tri-band transceiver, an RTL-SDR dongle and a Raspberry Pi with a TFT screen for tracking satellites. The Pi and SDR might also be part of a NOAA satellite receiver like the one [Fuzz] describes in a separate video; such a setup would be very valuable in natural disaster responses. Everything is powered by a 12-volt battery which can be charged from a small solar panel.

[Fuzz] is ready for action, and while we genuinely hope he and other hams won’t be needed in Florida, it doesn’t seem likely at this point. You can read more about the public service face of ham radio, or about an even more capable go-box.

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