Doug Lung /
RF Shorts for Dec. 2, 2013
A review of RF-related news during the past week
Pole-Climbing Robot Could Aid Post-Disaster Communications Restoration
Glenn Bischoff has an article on Urgentcom.com describing a robot that can climb most types of light poles carrying an antenna. It is small enough to fit in any emergency vehicle and was constructed for about $300 using off-the-shelf parts. A windshield wiper motor drives the worm gear and wheels that propel it up the pole. A clamping mechanism prevents it from sliding back down once power to the motor is removed.
This device didn't come from a university laboratory or a high-tech manufacturing company; it was developed by high school students Devlin Murray and Chris Blackwood. Their invention attracted a lot of attention and they were awarded the Radio Club of America's 2013 Young Achiever Award.
John Powell, chairman of the National Public Safety Communications Council's (NPTSTC) technology committee said: “I’m going to try to get them to write something up that we can post on the NPSTC website. What emergency-response agency doesn’t have light poles in their jurisdiction? And, around an incident, that elevation is all you need--you don’t need to get 100 feet into the air. If you’re talking about covering a couple of blocks around an emergency incident, 30 feet is probably all you need.”
For more on the invention and the inventors, read Pole-climbing robot has potential for disaster-response communications
by Glenn Bischoff in the Urgentcom.com “Urgent Matters” column.
Interest Resurfaces in Tropo Communications
Caleb Henry's article Comtech Systems Receives $2.4 M Contract for New Troposcatter Communications System
covering Comtech Systems' contract to install a digital over-the-horizon microwave communication system for a deep-water tension-leg oil platform for a major international oil company prompted me to take a closer look at the state of troposcatter communications and Comtech Systems.
I found a Comtech whitepaper The Resurgence of Troposcatter Communications in the Military
that offers an excellent description of how troposcatter systems work. The whitepaper says, “Troposcatter radio systems, also known as beyond line of sight microwave, or simply tropo, provide communications over the horizon by using a diffraction or scattering radio path through the troposphere.” It continues, “Using scattering to achieve beyond line of sight communications means that the path loss is higher than normal line of sight microwave transmission. This in turn requires high gain antennas, high power amplifiers and modem designs to account for the additional energy loss in both fast and slow fading conditions.”
The whitepaper describes current military troposcatter systems and notes that data rates up to 40 Mbps have been achieved by combining the output of two modems. Systems typically use C-band (4.4 to 5.0 GHz) but systems could be deployed using S-band (2.0 to 4.0 GHz). While X-band and even Ku-band have received some attention, the whitepaper notes spectrum availability, higher cost and reduced performance have led most military planners to the conclusion that C-band is most effective for troposcatter communications.
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