Wireless Systems Design

60 kHz Wireless

Yes, that is not a mistake. It is 60 kiloHertz, not 60 MHz or 60 GHz. There actually is wireless activity at that frequency—at least in the U.S. Specifically, the time standard station WWVB, located near Fort Collins, Colorado, broadcasts on that frequency. The National Institute of Standards and Technology (NIST) operates three radio stations that continuously broadcast accurate time and frequency information. It transmits time info at a rate of 1 bit per second using pulse width modulation. The BCD time code contains year, day of the year, hour, minute, second, and time flags for daylight savings time, leap years, etc.

With a wavelength of 5000 meters, you can only imagine the antenna size problems. They have four 122-foot towers arranged in a diamond shape. They use a wire capacitive loading "hat" and use the down leads as part of the radiators. An automatic variable inductor or variometer is used to tune the antenna to varying conditions—especially ice, snow, and wind. The transmitter cranks out 38 kW with an effective radiated power (ERP) of 50 kW. It easily blankets most of the U.S.

NIST also operates the more familiar shortwave time signal broadcasts on 5, 10, and 15 MHz with 10 kW each and at 2.5 and 20 MHz with 2.5 kW. Station WWVH in Kauai, Hawaii operates on the same frequencies with lower power. For details go to the website at http://tf.nist.gov/stations/wwvb.htm.

But that is not what I wanted to tell you. The new watch I got for my birthday from my charming wife has a built-in WWVB receiver. It automatically syncs the digital watch to the time signal. So the time is, as Academy Award winner Marisa Tomei says in the 1991 movie My Cousin Vinnie, "dead on balls accurate,” I like that. The watch is made by La Crosse Technologies. I don't know where my wife got this one, but I have seen it promoted in more than a few mail order catalogs. Total price: $29.95 plus shipping and handling. Isn't wireless great? And I suppose you think I am still the radio geek I was as a teen.

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