RF Shorts for Dec. 6, 2013

Audiovox Mobile DTV Receiver Reviewed
Edward Baig has a nice review of mobile DTV in his USA Today article Audiovox turns smartphone or tablet into a TV (opens in new tab). He writes, “Dyle's mobile TV signal is not high-definition, but not bad for the smaller screen. Except for the odd momentary hiccup, I managed to hold onto a signal during a 40-minute bus ride from northern New Jersey toward Manhattan, at least until I got into the Lincoln Tunnel. Audiovox promises about four hours of battery life before you have to charge it via USB.”

His main criticisms were the lack of stations and the blackout of NFL games. He says, “There are way too few station options. Too bad because the Dyle/Audiovox pitch would otherwise appeal to the person who can't get enough TV: Once you've paid for the gizmo--which can be found for as little as $100--you won't be subjected to ongoing subscription fees. That's different from rival mobile TV service Aereo, which charges $8 a month under its basic plan. Moreover, because you don't rely on cellular using the Audiovox, there's no data plan to put at risk.”

I've been traveling around the country with my Audiovox Mobile DTV hot spot. I've found very few areas where the device doesn't work. However, I have to agree with Baig that the limited number of stations available limits its usefulness. Most of my TV viewing is on PBS and so far Atlanta is the only market I've visited recently where the main PBS schedule is available on mobile DTV.

How to Hijack a Drone
You've probably seen stories in the popular press about a hack that allows someone to hijack and control drones. Many of these articles provide little detail on how it works and the hack's limitations. For more technical details, I recommend visiting http://samy.pl/skyjack/ to read Samy Kamkar's description of how his hack works and what's involved in implementing it.

Kamkar says, “Using a Parrot AR.Drone 2, a Raspberry Pi, a USB battery, an Alfa AWUS036H wireless transmitter, aircrack-ng, node-ar-drone, node.js, and my SkyJack software, I developed a drone that flies around, seeks the wireless signal of any other drone in the area, forcefully disconnects the wireless connection of the true owner of the target drone, then authenticates with the target drone pretending to be its owner, then feeds commands to it and all other possessed zombie drones at my will.”

Note that this hack will not work with large drones like those used by the military or police. I would expect them to use something more robust than Wi-Fi to control their drones. Also, as you will read, this only works with the popular Parrot drones, which are usually sold to hobbyists.

These limitations aside, Kamkar's hack could certainly be useful if your neighbor starts buzzing your house with his or her new Parrot AR Drone!

700 MHz LTE Phones Interfere With Cable Channels
Cable TV spectrum ranges from lower than 50 MHz (for data) to higher that 700 MHz. It isn't surprising, therefore, that LTE cell phones operating in the band that used to be occupied by TV Channels 52-69 are causing some problems for cable TV boxes that aren't adequately shielded. ArsTechnica.com writer Jon Brodkin describes some of the problems seen in Raleigh, N.C. by WRAL-TV engineer Sam Matheny. In his article Time Warner Cable TV goes blurry in presence of Verizon LTE phones – Cable using same spectrum as Verizon, unable to block out interference, Brodkin writes, “Those channels are transmitting on the same 700 MHz spectrum also used by Verizon, and the cable system is seemingly unable to block out the signals. The WRAL-TV story points the finger at cable boxes being incapable of dealing with interference, although it's also possible that some bad coax could be causing the problem. Cable systems are allowed to use the same spectrum as wireless carriers, as long as they keep the transmissions on the wire and don't interfere with cellular service.”

For details, see the WRAL.com article Spectrum battle puts 4G, cable in conflict. It offers some solutions to the problem: “People also can put their phones on airplane mode. That solves the interference with TV, but they won't be able to use their phones until switching back. Another solution involves turning off the 4G service and using Wi-Fi to access the Internet.” Time Warner suggested taking the phone to another room.

Comments and RF related news items are welcome. Email me at dlung@transmitter.com.

Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.