TAG: letters

Letters: Galileo Sync, GLONASS Scoop, an Open Letter

June 23, 2014By

June Cover Story In the June issue’s cover story, “Interchangeability Accomplished,” is a paragraph headed, “Satellite Intersystem Biases,” which appears to assert that Galileo System Time (GST) is 3 seconds ahead of UTC. However, in the version of the Galileo Signal In Space Interface Control Document posted at: http://ec.europa.eu/enterprise/policies/satnav/galileo/files/galileo-os-sis-icd-issue1-revision1_en.pdf, paragraph 5.1.2 appears to indicate that Galileo System Time (GST) was synchronized, at... read more

Letters to the Editor: Of Services, Commercial and Non

June 1, 2014By
Veripos ground receiver station network.

In a comment posted to GPS World’s website on Tony Murfin’s recent column, “Hexagon’s Acquisition of Veripos: Why Did This Go Down?”, Craig Roberts of Australia wrote: Tony, I do take issue with the suggestion that the International GNSS Service (IGS) is somehow inferior and not reliable. I understand that Veripos is a commercial service designed for specific markets, but... read more

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Letters to the Editor

October 1, 2013By
Constellation snapshot for a specific date/time: GPS week 1749 (725) and GPS seconds 86400 = July 15, 2013, at midnight GPS Time.

Orbital Planes, Nightmares, Pioneers Good morning, Dr. Langley, I have a seven-year-old drawing of GPS satellites in their orbital planes that I found (can’t recall where) some years ago, either on a website or from a colleague who attended some GPS forum. Would you know of a site where I can find current information on GPS satellite locations, which ones... read more

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Letter to the Editor: Our First Mistake

December 1, 2012By

Our first mistake is to presume an environment of perfection and security. Nothing is foolproof and spoof-free. Every product or service is an envelope of packaging that can be opened, peeled back, reversed engineered, and replicated. I have seen “ultimate security” defeated repeatedly. GPS is no exception, of course. We put our signatures and seals on these things; enterprising competitors,... read more

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Letter to the Editor: Using One Part of GPS, Ignoring Another

October 1, 2012By

The article “Drone Hack” in the August issue of GPS World and Todd Humphreys’ testimony before a House Subcommittee overseeing the Department of Homeland Security cited results of a spoofing experiment Humphreys conducted with University of Texas colleagues, demonstrating that a drone helicopter, navigating principally on the civil GPS signal, could have its vertical channel spoofed, causing it to descend.... read more

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Letters to the Editor: Antennas and the Human Body

March 1, 2012By

We have been reading with much interest the Innovation column, “GNSS Antennas and Humans” (Innovation, February issue). As the interaction with the human body is something many companies designing GPS into their products do not consider, it is great to see this topic being given some recent attention. We do feel, however, that we should comment on some issues we see in the article, especially as one of our antennas has been used as part of the testing. read more

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Letters to the Editor: The Cost of Reliability

December 1, 2011By

Letters to the Editor: The Cost of Reliability read more

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Letters to the Editor

August 1, 2011By

August's letters to the editor. read more

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