$40 Antenna Analyzer with Arduino and AD9850

If you are a hacker, you might consider ham radio operators as innovative. Most people, however, just see them as cheap. So it is no surprise that hams like [jmharvey] will build an antenna analyzer from a DDS module and an Arduino instead of dropping a few hundred dollars on a commercial unit. As he points out, you probably only need an analyzer for a day or two while you set up an antenna. Unless you are a big time antenna builder, the unit will then sit idle on the shelf (or will wind up on loan to hams even cheaper than you are).

The design is rooted in another proven design, but changed to take advantage of parts he happened to have on hand. Although the build is on a universal circuit board, [jmharvey] used Eagle to lay out the circuit as though it were a PCB. Since placement can be important with an RF circuit, this isn’t a bad idea. It’s always easier to move stuff around on the screen than on the perf board.

Since this is a no frills, unit, you are expected to grab the output from the Arduino and manually put it in a spreadsheet to plot the results. There is another version of the Arduino code that drives an OLED screen, although you still need a PC to kick the process off. One interesting feature of the Arduino code is how it deals with the nonlinear nature of the diodes used in the circuit. After plotting the values with known loads, [jmharvey] broke the diode operation into three regions and used different equations for each region. Even so, he warns that readings higher than 1:1 VSWR are only accurate to 10% or 20% – still good enough for ham shack use.

If you want an antenna analyzer for $40 (or less, if you have a good stock of parts) this looks like a worthwhile project. If, however, you want to repurpose it to Rickroll your neighbor’s AM radio, you might want to go with the commercial unit.

Click past the break to see the analyzer in action.

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How To Build A ProxyHam Despite A Cancelled DEFCON Talk

A few days ago, [Ben Caudill] of Rhino Security was scheduled to give a talk at DEFCON. His project, ProxyHam, is designed for those seeking complete anonymity online. Because IP addresses can be tied to physical locations, any online activities can be tracked by oppressive regimes and three letter government agencies. Sometimes, this means doors are breached, and “seditious” journalists and activists are taken into custody.

With the ProxyHam, the link between IP addresses and physical locations is severed. ProxyHam uses a 900MHz radio link to bridge a WiFi network over miles. By hiding a ProxyHam base station in a space with public WiFi, anyone can have complete anonymity online; if the government comes to take you down, they’ll first have to stop at the local library, Starbucks, or wherever else has free WiFi.

[Ben Caudill] will not be giving a talk at DEFCON. It wasn’t the choice of DEFCON organizers to cancel the talk, and it wasn’t his employers – [Ben] founded and is principal consultant at Rhino Security. The talk has been killed, and no one knows why. Speculation ranges from National Security Letters to government gag orders to a far more pedestrian explanations like, “it doesn’t work as well as intended.” Nevertheless, the details of why the ProxyHam talk was cancelled will never be known. That doesn’t mean this knowledge is lost – you can build a ProxyHam with equipment purchased from Amazon, Newegg, or any one of a number of online retailers.

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HamShield Puts Your Arduino On The Radio

Anybody can grab a USB TV tuner card and start monitoring the airwaves, but to get into the real meat of radio you’ll need your amateur radio license. Once you have that, the bandwidth really opens up… if you can afford the equipment. However, [spaceneedle] and friends have dramatically lowered the costs while increasing the possibilities of owning a radio by creating this ham radio shield for the Arduino.

The HamShield, is a versatile shield for any standard Arduino that allows it to function like an off-the-shelf radio would, but with a virtually unlimited number of functions. Anything that could be imagined can be programmed into the Arduino for use over the air, including voice and packet applications. The project’s sandbox already includes things like setting up mesh networks, communicating over APRS, setting up repeaters or beacons, monitoring weather stations, and a whole host of other ham radio applications.

HamShield operates on a wide range of frequencies and only uses a 250 mW amplifier. The power draw is small enough that the HamShield team operated it from a small solar panel, making it ideal for people in remote areas. The project is currently gathering funding and has surpassed their goal on Kickstarter, branding itself appropriately as the swiss army of amateur radio. The transceiver seems to be very robust, meaning that the only thing standing in the way of using this tool is simply writing the Arduino code for whatever project you want to do, whether that’s as a police scanner or even just a frequency counter. And if you want to follow along on hackaday.io, the project can be found here.

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Accessing A PBX Through Voice Channels

[Alessandro] is an unlucky VoIP PBX administrator that frequently has to deal with very, very dumb network policies. Often times, he’ll have to change something on his setup which requires him to go out to his client’s location, or ask a client to use Teamviewer so the appropriate change can be made from behind a firewall.

This isn’t the solution to the problem. It will, however, fix the problem. To get around these firewalls, [Alessandro] is using the voice channels he already has access to for changing configurations on his VoIP boxes.

The implementation of this uses the AX.25 amateur radio modules that can be found in just about every Linux distro. This, and an Alsa loopback device, allows [Alessandro] to access a terminal over a voice-only network. Is it a hackey kludge? Yep. Is it just a little bit dumb? So are the network policies that don’t allow [Alessandro] to do his job.

This build isn’t too dissimilar than a bunch of modems from the old BBS days, albeit with vastly more powerful software. [Alessandro] says you’re only going to get about 38400bps out of this setup, but it beats begging for help for remote access.

The Biggest Day At Hamvention

We capped off day-2 of the Hamvention with an unexpected rain shower, and some arcing back in the hotel room.  Historically, Saturday is the best attended day of the show.  As normally, we spent most of the day outside in the flea market.  One of our friends allowed us to use his AN/GRC-9 army surplus radio to check into one of the nets.  The radio was powered by hand-crank.  Later, we attended a forum on the construction of HF antennas for camping trips, and obtained parts for our project back in the room. More about that later?  Overall, a great day.

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Hamvention Just Getting Started

For one weekend in May, the landscape of Dayton, Ohio is dominated by ham radio operators. The Dayton Hamvention (“ham-convention”), sponsored by the Dayton Amateur Radio Association, is the preeminent gathering of hams from around the world. This is where industry rolls out new products, friends gather to catch-up, and old equipment is “re-distributed” amongst willing parties in the sprawling swap meet which subsumes the entire Hara Arena parking lot where you can find almost anything and meet some of the most interesting people.

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Hamvention 2015, Less Than One Week Away!

The largest amateur radio and electronics swap meet on the planet is less than one week away.  Will you be there?

The Dayton Hamvention has been an annual swap meet since 1952.  There were 24,873 attendees during last year’s hamvention alone, that is a huge number of radio enthusiasts in one place!

For those of you interested in using vintage and used test equipment you can find anything at Hamvention.  I built my entire laboratory form equipment purchased here.   It has often been said, ‘if you can’t find it at Hamvention you don’t need it.’

This year Scott Pastor (KC8KBK) and I will be covering Hamvention for Hackaday.  We plan to provide one update after each day of Hamvention summarizing the day’s events.  We hope to see you in Dayton next week!