radio

564 Articles

Hackaday Prize Entry: Ground Penetrating Radar

April 29, 2015 by 33 Comments

This year’s Hackaday Prize is heating up, and right now there are quite a few projects in the works covering domains that are rarely, if ever, seen coming out of a garage or a workshop. One of the most interesting is [Glenn Powers]’ Open Ground Penetrating Radar. It’s exactly what the title says: an open-source radar system that can see into the Earth for less than $500.

While ground penetrating radar is great for archaeology and people searching for hoards buried in the middle of farmland, the biggest application is safety. You need only to Google “Florida sinkhole” to see the value of peering into the Earth.

[Glenn] is building his ground penetrating radar with a bare minimum of parts. A Baofeng VHF/UHF My First Radio™ serves as the signal generator, the controller is just an optoisolator, and the switch controller is a 7404 hex inverter. It literally can’t get simpler than that.

Of course these components can only be assembled into a simple radar, and the real value of a ground penetrating radar is the ability to map an area. For that, [Glenn] is bringing out a Pi and a GPS dongle to control the whole thing. Visualization is provided by none other than the US Navy. If it works for submarines, it should work for a metal cart, right?

It’s a great project, not only in the fact that it could help a whole bunch of people, but as a prime example of doing so much without tens of thousands of dollars in test equipment.

The 2015 Hackaday Prize is sponsored by:

Cyclist Pulled Over For Headphones Builds Neighborhood Shaking Bicycle Boombox

April 13, 2015 by 86 Comments

Riding around with headphones on is not the safest of things; those people are trying to could hit you! [Victor Frost] was actually pulled over for doing it. Although the bicycle police didn’t ticket him, they did push him over the edge to pursuing a compromise that lets him listen to tunes and perhaps still hear the traffic around him.

The build puts 200 Watts of audio on his rear luggage rack. He used a couple of file totes as enclosures, bolting them in place and cutting one hole in each to receive the pair of speakers. The system is powered by two 6V sealed lead-acid batteries which are topped off by a trickle-charger when the bike is parked.

Looking through this log we almost clicked right past this one. It wasn’t immediately apparent that this is actually version four of the build, and these are completely different spins each time. The top-down view of plastic-tacklebox-wrapped-v3 is sure to make you grin. Video overviews of the first two versions are linked in [Victor’s] details section of the project page linked at the top of this post. The progress is admirable and fun time digging through. They’re all quite a bit different but bigger, better, and more self-contained with each iteration.

Okay, okay, maybe this isn’t going to shake the neighborhood… until he adds a Bass Cannon to it.

Transmitting HD Video From A Raspberry Pi

March 28, 2015 by 30 Comments

It’s been a few years since the RTL-SDR TV Tuner dongle blew up the world of amateur radio; it’s a simple device that listens in on digital television frequencies, but it’s one of those tools that’s just capable enough to have a lot of fun. Now, we have a transmitting dongle. It’s only being used to transmit live HDTV from a Pi, but that in itself is very interesting and opens up a lot of possible builds.

The key piece of hardware for this build is a UT-100C DVB-T modulator. It’s a $169 USB dongle capable of transmitting between 1200-1350 MHz, and with a special edition of OpenCaster it’s possible to transmit over-the-air TV. There’s no amplifier, so you won’t be sending TV very far, but it does work.

On the Raspberry Pi side of the build, the standard camera captures H.264 video with raspivid, which is converted to a DVB compliant stream using ffmpeg. These are well-worn bits of software in the Raspberry Pi world, and OpenCaster takes care of the rest.

While this seems like the perfect solution to completely overbuilt quadcopters, keep in mind transmitting on the 23cm band does require a license. Transmitting in the UHF TV bands is a bad idea.

Horn Antenna

Building A Horn Antenna For Radar

March 22, 2015 by 15 Comments

So you’ve built yourself an awesome radar system but it’s not performing as well as you had hoped. You assume this may have something to do with the tin cans you are using for antennas. The obvious next step is to design and build a horn antenna spec’d to work for your radar system. [Henrik] did exactly this as a way to improve upon his frequency modulated continuous wave radar system.

To start out, [Henrik] designed the antenna using CST software, an electromagnetic simulation program intended for this type of work. His final design consists of a horn shape with a 100mm x 85mm aperture and a length of 90mm. The software simulation showed an expected gain of 14.4dB and a beam width of 35 degrees. His old cantennas only had about 6dB with a width of around 100 degrees.

The two-dimensional components of the antenna were all cut from sheet metal. These pieces were then welded together. [Henrik] admits that his precision may be off by as much as 2mm in some cases, which will affect the performance of the antenna. A sheet of metal was also placed between the two horns in order to reduce coupling between the antennas.

[Henrik] tested his new antenna in a local football field. He found that his real life antenna did not perform quite as well as the simulation. He was able to achieve about 10dB gain with a field width of 44 degrees. It’s still a vast improvement over the cantenna design.

If you haven’t given Radar a whirl yet, check out [Greg Charvat’s] words of encouragement and then dive right in!

How Cheap Is Cheap?

March 14, 2015 by 21 Comments

The Nordic Semiconductor nRF24L01 is the older sibling of the nRF24L01+ and is not recommended for new designs anymore. Sometimes, if you’re looking for a cheaper bargain, the older chip may the way to go. [necromant] recently got hold of a bunch of cheap nrf24l01 modules. How cheap ? Does $0.55 sound cheap enough?

Someone back east worked out how to cost-optimize cheap modules and make them even cheaper. At that price, the modules would have severe performance limitations, if they worked at all. [necromant] decided to take a look under the hood. First off, there’s no QFN package on the modules. Instead they contain a COB (chip on board) embedded in black epoxy. [necromant] guesses it’s most likely one of those fake ASICs under the epoxy with more power consumption and less sensitivity. But there’s a step further you can go in making it cheaper. He compared the modules to the reference schematics, and found several key components missing. A critical current set resistor is missing (unless it’s hiding under the epoxy). And many of the components on the transmit side are missing – which means signal power would be nowhere near close to the original modules.

The big question is if they work or not ? In one test, the radio did not work at all. In a different setup, it worked, albeit with very low signal quality. If you are in Moscow, and have access to 2.4Ghz RF analysis tools, [necromant] would like to hear from you, so he can look at the guts of these modules.

Thanks to [Andrew] for sending in this tip.

Measuring Filters And VSWR With RTL-SDR

March 14, 2015 by 5 Comments

Once again the ubiquitous USB TV tuner dongle has proved itself more than capable of doing far more than just receiving broadcast TV. Over on the RTL-SDR blog, there’s a tutorial covering the measurement of filter characteristics using a cheap eBay noise source and an RTL-SDR dongle.

For this tutorial, the key piece of equipment is a BG7TBL noise source, acquired from the usual online retailers. With a few connectors, a filter can be plugged in between this noise source and the RTL-SDR dongle. With the hardware out of the way, the only thing remaining is the software. That’s just rtl_power and this wonderful GUI. The tutorial is using a cheap FM filter, and the resulting plot shows a clear dip between 50 and 150 MHz. Of course this isn’t very accurate; there’s no comparison to the noise source and dongle without any attenuation. That’s just a simple matter of saving some scans as .csv files and plugging some numbers in Excel.

The same hardware can be used to determine the VSWR of an antenna, replacing the filter with a directional coupler; just put the coupler between the noise source and the dongle measure the attenuation through the range of the dongle. Repeat with the antenna connected, and jump back into Excel.

Simple Superheterodyne SW Receiver Harks Back Almost 100 Years

March 8, 2015 by 13 Comments

Early radio receivers worked on a principle called Tuned Radio frequency (TRF), patented in 1916. They weren’t very easy to use, requiring each stage to be tuned to the same frequency (until ganged capacitors made that a bit easy). The Superheterodyne design, devised in 1918, was superior, but more expensive at that time. Cost considerations led adoption of the Superhet design to lag behind TRF until almost 1930. Since then, until quite recently, the Superhet design has been at the heart of a majority of commercial radio receivers. Direct Conversion Receivers were devised around 1930, but required elaborate phase locked loops which restricted their use in commercial receivers. The point of all this background is that the Superhet design has served very well for more than 90 years, but will soon be rendered redundant once Software defined Radio (SDR) becomes ubiquitous. Which is why this study of the simple Superheterodyne shortwave receiver deserves closer study.

[Dilshan] built this two transistor and two IF transformer based superheterodyne radio designed to receive 13m to 41m bands. The whole build is assembled on a breadboard, making it easy to teach others to experiment. [Dilshan] offers very useful insights into antenna, rod coil and IF transformer parameters. To dive in to Radio architecture, check this post on Amateur Radio. And if you would like to get a closer look at Antique Radios, check this post on Restoring Antique Radios.