Selected Daily Notes Archive (Home Page has current notes)
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January 17, 2004
More on Mars Comm
I've written below on communication between Earth and the Mars' Rover. But this wonderful graphic from the Chronicle tells the story in a more pictorial form. Click here to view. (147K). Quite nice.
January 16, 2004
Cell phones on airplanes in flight
While you can't use your cell phone in flight on commercial airliners now, that may soon change. I'm working on a preliminary page that explains this.
January 15, 2004
Too much to keep track of
Added an article by Julian Macassey, N6ARE, to the site. It's the essential article on how telephones work. It is technical but if you want to learn telephony then you need to understand this page. It was first published in Ham Radio Magazine, September 1985.
Mark van der Hoek explains antenna polarization, db's and the mysterious image below in yet another page in the cellular telephone basics series. Scroll all the way down to the bottom of the page.
January 13, 2004
Good, current writing
The lead article in the new Ericsson Review discusses mobile communications and health. Well written and researched:
http://www.ericsson.com/about/publications/review/
And Ericsson continues to publish the well done On, a chatty, colorful read that focuses on current and soon to be wireless offerings:
http://www.ericsson.com/about/publications/onmagazine/
Alcatel devotes their latest quarterly entirely to wireless:
http://www.alcatel.com/atr/
Each magazine offers free subscriptions free through the mail, a great service. I like my information electronically available, to have an online version, but I still prefer reading a regular, non .pdf magazine.
January 13, 2004
Hanjoo Kim of the IITA (Institute of Information Technology Assessment), Daejoen, South Korea, supplies this nice outline of wireless in Korea. He adds that number portability has been required for some time and that, as in America, many problems and much confusion have resulted.
Brief history of mobile communications in Korea
From mid-1960s : IMTS service for government use only. [Editor's note: Motorola sold IMTS systems throughout the world.)
March 1984 : Inauguration of KMT (Korea Mobile Telecommunications Co.,) as a subsidiary of KTA (Korea Telecommunications Authority; the government-owned communication service carrier. It is now KT (Korea Telecom), a privatized telecom company)
May 1, 1984 : KMT begins AMPs service.
June, 1994 : KMT privatizes, with SK (Sun-Kyung Group) becoming the 1st major stockholder of KMT.
January, 1996 : Shinsegi Telecom (the second cellular service carrier in Korea) begins CDMA service in the Incheon area (very near to Seoul).
April, 1996 : KMT begins CDMA service in Seoul area. (Sun-Kyung Group Telecom)
March, 1997 : KMT changes name to SK Telecom.
October, 1997 : Three PCS service carriers (KT Freetel, LG Telecom, Hansol PCS) begin CDMA service at 1.7GHz.
April, 2000 : SK Telecom acquires Shinsegi Telecom. Retires the Shinsegi Telecom name.
October, 2000 : cdma2000-1x service launches.
December, 2000 : SK Telecom and KT Freetel get IMT-2000 licenses for W-CDMA.
May, 2001 : KT Freetel acquires Hansol PCS. KT Freetel retires the Hansol name.
August, 2001 : LG Telecom gets the IMT-2000 license for cdma2000 technology.
May, 2002 : cdma2000-1x EV-DO service begins. (SK Telecom insists that this service began in January 2002. But in the official statistics, subscribers to cdma2000-1x EV-DO first appear in May, 2002.)
December 2003 : Launch of W-CDMA service for field trial.
Editor's note. Some additional, though dated material was at the external link below:
http://www.3gnewsroom.com/country/south_korea.shtml
January 8, 2004
Consumer Reports is out with their annual cell phone plan report. It's in the February issue which should be going on newstands now. I have their summary here which makes for interesting reading. No carrier comes out well in their survey, and each service plan seems deliberately confusing so that subscribers can't easily compare rates and services.
The wireless industry continues to promise more than they can deliver, and this has been happening every year since 1984. Customers want large coverage areas, few dropped calls, and good audio quality. The industry responds by providing deceitful coverage maps, routinely dropped calls, and connections filled with static, no sidetone, or voices that make us sound like Donald Duck. Yes, cellular radio technolgogy is wonderful and I am glad it is here. I just wish the wireless industry would conduct itself in a more honest way, explaining radio's limitations as well as its benefits.
January 6, 2004: 4:30 pm. update
The line art below is from a 1960's Bell System ad detailing their efforts with communication satellites. The ad shows an early computer simulation, possibly drawn on a plotter, quite a contrast from today's marvelous, animated, full color renderings. Click here to view the entire ad in much finer detail. Warning: it's quite a large file.
I've had difficulty finding out exactly how long it takes for a radio signal to go from Earth to Mars. Turns out that many answers can be correct since the distance from our planet to Mars varies so greatly. Here's the problem well explained:
Question
How long does it take for a radio signal to go from Earth to Mars?
Asked by: Richard Boulais
Answer
Radio signals are electromagnetic waves, such as light or X-ray. The speed of electromagnetic waves in vacuum, is 300000km/sec (approximately).
In order to calculate the time of travel with this speed from Earth to Mars, we need to know the distance.
When the Mars and the Earth are at the opposite sides of the Sun, the distance is the largest: approximately: 378 million km. The time needed for an electromagnetic wave to cover this distance is approximately: 21 minute.
The closest distance between Mars and Earth is 78 million km, the time in this case is: 4.3 min.
So the time of travel between Earth and Mars is between 4.3 minutes and 21 minutes, depending on the actual distance between the two planets.
Answered by: Ferenc Szekely, Ph.D., Physicist, ELTE, Budapest, Hungary
Source: http://www.physlink.com/Education/AskExperts/ae381.cfm
January 4, 2004
You might as well be on Mars
The United States has again returned to the Red Planet. The Rover's radio gear communicates directly with earth or to orbiting satellites above Mars. At a data rate equal to most terrestrial cellular networks!
Sending data over cellular networks has always been slow. Cellular radio was built on low bandwidth rates to conserve spectrum and because voice was the first priority. Only now are technologies like EDGE and GPRS slowly improving data transfer speeds.
But a typical file transfer on a present cellular radio system, today, while driving about in a car or truck, gets no better results than NASA does from Rover, millions of miles in space: from 3,500 bits per second to 12,000 bits per second. Remember that old 14.4 modem you used to have? NASA would love that top speed and you might too, getting that new picture phone of yours to work.
At the bottom of this page I write about how telephony is no longer possible when distances stretch far into space:
http://www.privateline.com/TelephoneHistory/soundwaves.html
And there's a mention of Britney Spears so you really should check it out. :-)
January 23, 2004
Ranch work today instead of web work. We're getting the property and equipment ready for spring.
It's too bad about the Martian Rover. It's having problems and NASA/JPL aren't sure what's wrong. See their press release below. Today it did communicate with Earth using a satellite orbiting Mars. Story from JPL below. This nice graphic from the San Francisco Chronicle shows how that communication link works. Click here to view. (147K).
"NASA's Spirit rover did not go to sleep today even after ground controllers sent commands twice for it to do so.:
"Shortly before noon, controllers were surprised to receive a relay of data from Spirit via the Mars Odyssey orbiter. Spirit sent 73 megabits at a rate of 128 kilobits per second. The transmission included power subsystem engineering data, no science data, and several frames of 'fill data.' Fill data are sets of intentionally random numbers that do not provide information."
"Spirit had not communicated successfully through Odyssey since the rover's communications difficulties began on Wednesday."
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