Hackaday Prize Finalist: A Network of Satellite Ground Stations

There are astonishing things you can do with a network of sensors spread across the globe, all connected to the Internet. Thousands of people have already installed hardware to detect lightning and flightaware gives out subscriptions to their premium service to anyone who will listen in to airplane transponders and send data back to their servers. The folks behind SatNOGS, one of the five finalists for The Hackaday Prize are using this same crowdsourced data collection for something that is literally out of this world: listening to the ever-increasing number of amateur satellites orbiting the planet.

There are dozens of cubesats and other amateur satellites flying every year, and they have become an extremely popular way of experimenting in a space environment, giving some budding engineers an awesome project in school, and testing out some technologies that are just too weird for national space agencies. The problem with sending one of these birds up is getting the data back down; a satellite will pass above the horizon of a single location only a few times a day, and even then for only minutes at a time. The SatNOGS team hopes to change that by planting receivers all around the globe, connecting them to the Internet, and hopefully providing real-time telemetry from dozens of orbiting satellites.

[Pierros] from the SatNOGS team was kind enough to sit down and answer a few questions for us about his entry to The Hackaday Prize. That’s below, right after their finalist video. Some of the SatNOGS team will also be at our Munich event where we announce the winner of the Prize.

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Fox Hunting with a Raspberry Pi

No, not a real fox! [KM4EFP] is a ham radio operator with a passion for fox hunting, which is an event where several radio operators attempt to find a broadcasting beacon (a “fox”) using radio direction finding techniques. [KM4EFP] has just built his own portable fox using a Raspberry Pi in a very well-built enclosure.

Since the fox could be outside for a while, the project was housed in a reasonably weatherproof ammunition case. A mount for an antenna was attached to the side, and it is hooked up to a GPIO pin on the Raspberry Pi. The entire device is powered by a 6000 mAh battery pack which allows the fox to broadcast long enough to be found.

The software running on the Raspberry Pi is very similar to the Pi FM transmitter program but it is specially made for ham radio broadcasting instead. Almost no extra hardware is needed to get the Pi broadcasting radio, as these software packages can drive the antenna directly from the GPIO pin. This is a great twist on the standard FM transmitter that ham radio enthusiasts everywhere can use to start finding those wily foxes!

Hacklet 19 – Ham Radio

19

Amateur, or ham radio operators have always been hackers. For much of the early 1900’s, buying a radio was expensive or impossible. Hams would build their own rigs, learning electronics and radio theory along the way. Time moves on, but hams keep hacking. Today we’re highlighting some of the best ham radio projects on Hackaday.io!

rtl

We start with [DainBramage1991] and his very practical RTL-SDR With Upconverter and Case. [DainBramage1991] fell in love with his low-cost RTL software defined radio dongle. He even added a Ham-It-Up upconverter to cover HF bands. The only problem was RF noise. the Realtek USB sticks tend to have little or no filtering, which means they are very susceptible to noise. [DainBramage1991] used the time-honored technique of insulating with copper clad board. Bits of PCB hold the RTL-SDR and upconverter in place. More PCB separates the two boards. Everything goes into a steel enclosure which keeps that unwanted RF at bay.

foxhunt-attenNext up is [Ryan Miller’s aka KG7HZQ]’s  ham radio fox hunt attenuator. Ham radio fox hunt’s don’t involve baying dogs or horses. In this case a fox hunt is a contest to find hidden low power transmitters. If you’ve never tried one, it’s a heck of a lot of fun. One of the challenges with a fox hunt is to find the direction to the transmitter when you’re very close. Even with directional antennas, reflections and swamped receivers make it hard to figure out just where the transmitter is. The solution is an attenuator, which simply reduces the signal to a more reasonable value. [Ryan] also used copper clad PCB for his circuit. Since the attenuator parts are soldered directly to the PCB, this is more of a Manhattan style design. Two ceramic 1k pots help him achieve his goal of near perfect linear attenuation. We’re betting this attenuator will help [Ryan] win some contests!

psdrWho says amateur radio won’t take you places? It may well be taking [Michael R Colton] to space! [Michael’s] project PortableSDR is one of the five finalists in The Hackaday Prize. We covered Michael earlier in the contest. PortableSDR started as a ham radio project: a radio system which would be easy for hams to take with them on backpacking trips. It’s grown into so much more now, with software defined radio reception and transmission, vector network analysis, antenna analysis, GPS, and a host of other features. We seriously love how [Michael] optimized a small LCD for waterfall display, tuning, and bandpass filter adjustment.

e2ra[W5VO] is working on an Ethernet to Radio Adapter. Every foot of coax in a radio system loses signal. Connections are even worse. It can all add up to several dB loss. [W5VO] wants to put an SDR at the antenna feed-point. With the signal path minimized, more watts make it out when transmitting, and more signal gets back to the receiver when listening. The interface between the SDR and host computer will be all digital; Ethernet to be precise. [W5VO] isn’t the first person to do something like this, microwave systems have had the transmitter and LNB at the antenna for years. That doesn’t take away from [W5VO’s] design at all  He’s been quiet for a while, but we’re hoping he continues on his design!

Where is everyone else? We’re a bit light on projects this week, but we have a good reason. There just aren’t enough ham radio projects on Hackaday.io! We’re hoping to change that though. Are you an amateur radio enthusiast? Document your project on the site. Get input from other hams and push the envelope! You might even find yourself on the Ham Radio List!

That’s all for this episode of The Hacklet. As always, QRX is next week. Same hack time, same hack channel, bringing you the best of Hackaday.io! 73’s!

Extrinsic Motivation: Smart Antenna Tracker for R/C Aircraft

Long distance FPV (First Person View) flying can be a handful. Keeping a video feed alive generally requires a high gain directional antenna. Going directional creates the chore of keeping the antenna pointed at the aircraft. [Brandon’s] smart antenna tracker is designed to do all that automatically. What witchcraft is this, you ask? The answer is actually quite simple: Telemetry! Many flight control systems have an optional telemetry transmitter. [Brandon] is using the 3DRobotics APM or PixHawk systems, which use 3DR’s 915 MHz radios.

The airborne radio sends telemetry data, including aircraft latitude and longitude down to a ground station. Equipped with a receiver for this data and a GPS of its own, the smart antenna tracker knows the exact position, heading and velocity of the aircraft. Using a pan and tilt mount, the smart antenna tracker can then point the antenna directly at the airborne system. Since the FPV antenna is co-located on the pan tilt mount, it will also point at the aircraft and maintain a good video link.

One of the gotchas with a system like this is dealing with an aircraft that is flying directly overhead. The plane or rotorcraft can fly by faster than the antenna system can move. There are a few commercial systems out there that handle this by switching to a lower gain omnidirectional whip antenna when the aircraft is close in. This would be a great addition to [Brandon’s] design.

TDOA (Time Difference of Arrival) Directional Antenna

tdoa-antenna-tutorial

We have posted articles in the past on directional antennas such as Yagi antennas used for transmitter hunting otherwise known as fox hunting. Those types of antennas and reception suffer from one major drawback, which is as you get close to the transmitter the S meter will go full scale. At which time the transmitted signal appears to be coming from all directions. To correct for this problem you need to use clever signal attenuators or change to a poor receiving antenna as well as tuning off frequency effectively making your receiver hard of hearing so that only the direct path to the transmitter is loudest.

There is another popular type of antenna that you can build yourself called a TDOA which stands for Time Difference of Arrival. [Byon Garrabrant N6BG]  shared a short video tutorial on the functionality of his home built TDOA antenna. Effectively this is an active antenna that uses a 555 chip or, in [Byon’s] case, a PIC chip to quickly shift between two receiving dipole antennas at either end of a shortened yardstick. In his explanation you learn that as the antenna ends move closer or farther from the source a 640 Hz generated audio tone will go from loud to very soft as the antennas become equal distance from the source. This type of directional reception is not affected by signal strength. This means you can be very close to a powerful transmitter and it will still function as a good directional antenna.

The current circuit diagram, BOM and source code are all available on [Byon’s] TDOA page.

The reason [Byon] used a programmable PIC instead of the 555 for his design is because he wants to add a few more modifications such as feeding back the audio output to the PIC in order to programmatically turn on a left or right LED indicating the direction of the transmitter. Furthermore, he plans on adding a third antenna in a triangular configuration to programmatically control a circle of 6 LEDs indicating the exact direction of the signal. When he finishes the final modifications he can drive around with the antenna array on his vehicle and the circle of LEDs inside indicating the exact direction to navigate.

We look forward to seeing the rest of the development which might even become a kit someday. You can watch [Byon’s] TDOA video after the break.

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PCB Antenna Reference Designs

Have you ever built a wireless project and weren’t sure how to make one of those awesome (and cheap!) PCB antennas? “What low-cost solutions does our Antenna Board #referencedesign contain?” said Texas Instruments (TI) recently via Twitter.  This older reference design contains some comprehensive designs for sub-1 GHz and 2.4 GHz antennas.

While TI’s documentation can be difficult to navigate, there are many hidden gems, and this is one of them. While TI created these designs for use with their wireless products, they will work on any device which utilizes the same wireless base frequency. For example, you could use any of the 2.4 GHz antennas with any Bluetooth, WiFi (2.4 GHz), or Bluetooth Low Energy chips. Simply open up their Antenna Selection Quick Guide document and navigate to the specific design for whichever antenna you would like to build.

For a more detailed overview of what goes into designing and testing a PCB antenna, check out this hack which we featured back in 2010. With the internet of things coming into its own, wireless projects will become more and more prolific, making PCB antennas more important than ever.

Improve Your HT Ham Radio by Adding a Counterpoise Antenna Wire

counterpoise

We found an interesting tip that might just improve the performance of those small affordable handheld ham radios called a “Handy Talky” or HT for short in ham vernacular. [RadioHamGuy] posted an interesting video on adding a counterpoise antenna wire to an HT. He claims it will noticeably improve both transmit and receive by making a quarter-wave monopole into a makeshift dipole antenna system.

Per his instructions you basically add a short wire to the antenna’s outer ground connection or to an equivalent case screw that’s electrically connected to the antenna’s ground side. Apparently this can be referred to as a Tiger Tail and does make it look like your HT has a tail. You would construct a counterpoise antenna wire 11.5 inch for VHF, 6.5 for UHF and about 19.5 inches for an OK performing dual band VHF/UHF radio.

Normally with a handheld radio the counterpoise (ground) is your own body as you are holding the HT. This is because the capacitance of your body makes a good counterpoise under normal conditions. It would be interesting to hear what others find for performance when adding a counterpoise antenna wire.

You can watch [RadioHamGuy’s] full construction tutorial video for multiple radio types after the break.

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