Improving a software defined radio with a few bits of wire

Impressed by the recent advances in the software defined radio scene, [Jason] picked up a $20 USB TV tuner dongle to check out his local airwaves. Unfortunately, the antenna included with the little USB dongle is terrible at receiving any signal other than broadcast TV. [Jason] wanted to improve his reception, so he got some wire and made his own discone antenna.

The discone antenna is ideally suited for [Jason]‘s setup – properly constructed, it’s able to receive over the entire 64 to 1700 MHz band the RTL-SDR dongle is able to read. To construct his antenna, [Jason] checked out [VE3SQB]‘s list of antenna design programs, got the dimensions of his antenna, and set to work attaching wire to PVC pipe.

The antenna is a massive improvement over the stock antenna included with the TV tuner dongle. After mounting his discone at the far end of his back yard, [Jason] started picking up a few blips from the transponders of passing aircraft.

Using mains wiring as an antenna

Make sure to brush up on your safety protocol if you undertake this project. The penalty for messing up when using live wiring as a radio receiver antenna is rather severe. But after reading about it in some old books [Miroslav] decided to give this technique a try.

We love the old-school chalk board he used to map out his test circuit. With safety in mind, he uses two high voltage capacitors in series. If these should somehow fail, there is also a fuse which would blow, disconnecting the apparatus from mains. But just to be sure, he isolated the circuit using a two coils. These step down the voltage, but would also burn out if hit with a voltage spike.

You can see the results he gets using the setup as an AM radio receiver in the video after the break. He tested against a meter long antenna and found that his setup far outperforms it. Actually, he found that a six foot extension cord which is not plugged into the wall will also outperform the 1m antenna. Something to keep in mind the next time the ball game isn’t coming in as clear as you would like.

[Read more...]

3G connected hotspot hangs out at your house

[Drug123] made the most out of this inconspicuous gray box on the gable end of his father’s home. It serves up a 3G Internet connection that was otherwise unavailable..

The project idea was sparked by the absence of wired or fiber optic broadband in the community where his dad lives. He knew some neighbors were using 3G connections, but he couldn’t get it to work inside the house. So he set about developing an external installation that would both communicate with the cellular network, and provide a WiFi connect to it. Hardware for that is relatively expensive; a USB 3G modem and a WiFi router with a USB port.

The box itself is made of plastic, but even without the Faraday cage effect that would have been formed by using a metal housing, the 3G modem’s internal antenna just doesn’t do the job. You can see that [Drug123's] solution was an external antenna which is mounted at the peak of the roofline. Inside the box there’s an exhaust fan to cool things off when they get too hot, as well as some power resistors which provide a heat source on the coldest nights. The low-cost build certainly fits the bill, and it’s not too hard on the eyes either.

FabLab helps the developing world set up long-distance wireless Ethernet

The wooden frame seen above hosts a parabolic reflector making up one side of a wireless network link. This is a Fab Lab project called FabFi which uses common networking hardware to setup long-distance wireless Ethernet connections. It’s a bit hard to tell in the image above, but the reflector focuses radio waves on the antennae of a router we’re quite familiar with, the Linksys WRT54G. It’s held upside-down in an enclosure meant to protect it from the elements. The node above manages to complete a connection spanning 2.41 miles!

One of the core values of the project is to develop hardware that is easy to build with limited resources, then to make that knowledge freely available. Anyone who has the ability to download and print out the 2D design file can build a reflector for themselves. As we’ve seen in other projects, paper stencils and hand tools can handle this job with no need for a laser-cutter (which was used for the prototype). WRT54G routers are inexpensive and the project uses the open source firmware OpenWRT. They can be run from 12VDC power which means a car battery works when mains power is not an option. The system has been running in Afghanistan for two years and hardware failure is still in the low single-digits.

[Thanks das_coach]

Antenna cannon for amateur radio

As an amateur radio enthusiast, [Andrew] sometimes has to set up impromptu antennas up to 160 meters in length. The easiest way to get these antennas off the ground is to drape them over trees, a feat normally accomplished by lofting fishing line into the air with a slingshot or bow and arrow. [Andrew] thought slings were so last century, so he came up with a spud gun inspired antenna launcher.

The launcher is built out of PVC and launches a foam filled tennis ball that can reel out 150 yards of Spectra line. In a moment of brilliance, [Andrew] decided to add an augmented reality HUD. The display is actually [Andrew]‘s phone running an app called Geocam that provides him with a display of elevation and azimuth overlaid on the phone’s camera feed. The results of [Andrew]‘s build are fairly impressive. The cannon was able to lob a tennis ball over a 110 foot tree at half the pressure rating of the PVC. The grouping was pretty tight as well, more than sufficient to run a line over a tree.

[Andrew]‘s antenna cannon is an awesome piece of work and unlike most french fry cutters, it’s a useful tool. If you’re interested in seeing 160 meter antennas heaved over the tops of trees, amateur radio field day is next month week, June 25th and 26th.

Long-range Bluetooth wardriving rig

bluetooth_wardriving

[Kyle] was digging through a box of junk he had lying around when he came across an old USB Bluetooth dongle. He stopped using it ages ago because he was unsatisfied with the limited range of Bluetooth communications.

He was going to toss it back into the box when an idea struck him – he had always been a fan of WiFi wardriving, why not try doing the same thing with Bluetooth? Obviously the range issue comes into play yet again, so he started searching around for ways to boost his Bluetooth receiver’s range.

He dismantled the dongle and found that the internal antenna was a simple metal strip. He didn’t think there would be any harm in trying to extend the antenna, so he soldered an alligator clip to the wire and connected the CB antenna in his truck. His laptop sprung to life instantly, picking up his phone located about 100 feet away in his house. He took the show on the road and was able to pick up 27 different phones set in discoverable mode while sitting in the parking lot of a fast food chain.

While it does work, we’re pretty sure that the CB antenna isn’t the most ideal extension of the Bluetooth radio. We would love to see what kind of range he would get with a properly tuned antenna.

Keep reading to see a quick demonstration of his improvised long-range Bluetooth antenna.

[Read more...]

Stepper Directed HDTV Antenna

Credit: http://www.instructables.com/id/Computer-controlled-OTA-TV-antenna/

Broadcast TV has come a long way from adjusting the rabbit ears on top of the set just to get a fuzzy black and white picture. While nowadays there are often HD signals broadcast in most areas, it can often still be critical to redirect an antenna to get the best possible signal. By harvesting a stepper motor from an old 5 1/2″ floppy drive, and using a PC’s parallel port to control it, this adjustment can be handled automatically. Broadcast tower locations are easily found online, and once you have calibrated your stepper to face North, you are on your way to free HDTV reception.

What we would like to see is this antenna attached to a HTPC, and some kind of script to automatically direct the antenna for the best possible signal for the current channel. If anyone out there makes this happen, be sure to let us know.

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