Dome Clock
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 Sunbeam Glass Dome Quartz Mantle Moon Phase Dial Clock Germany 882 1081Vintage  US $56.95
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 Disney Cinderella Anniversary Clock US $24.99
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 COUNTRY PRIMITIVE LIVE LAUGH LOVE WALL SALTBOX HOUSE WILLOW BATTERY CLOCK NEW US $20.00
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 ELGIN QUARTZ ANNIVERSARY MANTLE SHELF GLASS DOME CLOCK US $24.95
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 Assorted Glass Domes Cloche Bell Jar Doll Clock Cake Cover Display Terrariums US $63.00
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 NEW GVI Video Plus Indoor Dome Security Camera AID 5151W 680 TVL 28 105mm US $34.33
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 VINTAGE LG GLASS DOME CLOCHE FOR CLOCK TAXIDERMY COVER WITH WOODEN BASE US $49.99
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 TIMEX GLASS DOME DESK MANTEL MANTLE SHELF CLOCK BEAUTIFUL GOLD COLOR $ 9 TALL US $9.99
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 Official NFL Dallas Cowboys Swivel Office Desk Photo Clock NEW Uline US $11.95
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 Disney Eeyore Glass Dome Anniversary Clock US $14.99
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 Medium Clear Glass Dome Cloche Clock Cover w Wood and Tile Base US $9.99
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 PRECIOUS MOMENTS ANNIVERSARY CLOCK US $29.95
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 Elgin Gold American Quartz Anniversary Mantel Clock Dome with Spinning Pendulum US $49.99
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 Precious Moments Anniversary Clock The World is a Better Place with Friends NEW US $19.99
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 PERSONALISED WWF WALL CLOCK US $14.20
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 3800 ULTIMATE WOODWORKING PLANS COLLECTION on DVD US $6.95
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 MIRABILIS JALAPA BROKEN COLORS Annual SEED US $.99
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 MIRABILIS IRREDECENT PINK ANNUAL SEED US $.99
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 Dome Wooden Non Ticking Silent Time Wall Clock 300DOM US $29.71
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 Digital Color Change Star Light Projection Alarm Clock US $2.99
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 Official NFL Dallas Cowboys Swivel Office Desk Clock NEW Uline US $12.95
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 TIMEX ANNIVERSARY CLOCK WITH WESTMINSTER CHIME BRAND NEW US $17.99
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 Rare Pottery Barn Solid Wood Desktop Alarm Clock Glass Dome Round Octagon US $50.00
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 Digital Alarm Clock Backlight Color Projection Music Projector LED Starry Sky L US $6.73
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 Vintage Anniversary Centennial Elgin Quartz Dome Clock with Westminster chime US $59.95
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 Russell Hobbs 14943 16 L Cordless Dome Kettle Polished Stainless Steel Black US $47.38
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 Ceramic White Irridescent Glaze Mantle Clock Victorian Style Electric US $8.50
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 Honeywell Professional HRSD8D1000 8 Channel Security System with 6 Cams NEW US $699.95
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 RETRO COLONIAL CLOCK CO 1870 QUARTZ WALL CLOCK WORKING NEW BATTERY US $2.99
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 Color LED Starry Backlight Sky Projection Music Projector Alarm Clock Digital B US $6.97
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 Disney fairies Tinkerbell Anniversary clock US $14.99
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 Clock Glass Dome 4 x 6 Display Clock Watch Pocketwatch Doll Globe NEW US $12.49
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 Thomas Kinkade Anniversary Clock Victorian Garden NIB US $25.00
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 DecoMates Home Decor Dome Wooden Non Ticking Silent Time Wall Clock US $29.71
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 Loricron Quartz Anniversary Black Forest Clock with Roman Numerals 2795 US $221.00
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 BLOCKS FORKS 400 Day Anniversary Jahresuhr Torsion Dome Clock Clock Parts 1x US $7.99
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 Set 3 Glass Domes Bell Jar Cloche Doll Clock Display Cake Covers Terrariums US $180.00
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 The Ultimate Office and Safety and Security Kit US $511.00
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 J0 LATEST 32 CAMERA CHANNEL CCTV DVR LAN USB AUDIO VGA US $2,399.80
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 Jiffy Professional Greenhouse US $31.99
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 Jiffy Easygrow Carefree Greenhouse US $25.99
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 2 Childrens Large Numbered Quartz Dome Clocks Run on 1 AA Battery US $4.50
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 Jiffy Pellet Greenhouse US $22.99
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 Brinkmann All In One Cooker US $179.99
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 Kay Home Cast Iron Fireplace US $269.99
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 Achla Designs Bird Cage Stand US $239.99
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 New LED Digital Color Alarm Clock Starry Star Sky Projection Music Projector US $9.39
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 Achla Designs Euphony Pavilion US $1,999.99
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 Achla Designs Rhapsody Pavilion US $2,079.99
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 Acctim Falkenburg Mantel Piece Clock Will look Great On Display 2 Colours US $34.74
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 Good Directions Medium Full Moon Party US $329.99
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 Sky Projection Backlight Color LED Music Projector Digital Alarm Clock Starry W US $6.97
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 Arundale Mandarin Sky Cafi Green US $77.99
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 Trend Lab Baby Butterfly Purple Wall Clock 100222 US $20.00
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 Disney Mickey and Minnie Collectible Anniversary Clock US $102.61
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 Karlsson Wood Glass Pendulum Wall Clock HUGE 24 Dia US $225.00 |
 Ashton Sutton Francesca Wall Clock ST3322AB US $77.99
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 Bedside Alarm Clock with Night Light Digital Dome Snooze LCD Reading Travel NEW US $11.99
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 Glass Dome Bell Jar Clock Display Cloche Garden Terrarium Cake Pastry Cover US $63.00
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 Vintage Desk Clock Ronbe 8 Day Germany FREE SHIPPING US $48.00
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 NEW 36172 WEDDING COUPLE SNOWGLOBE US $19.08
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 Tropical Beach Hut Wooden Trash Bin Wastebasket US $42.88
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 Vintage Glass Dome w Wood Base 8 x 12 tall Display Case Doll Clock Taxidermy US $47.34
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 Quartz Metal Alarm Clock New in Box US $25.00
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 Waltham Anniversary Clock Elvis Presley 2 US $25.99
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 Areaware Numbers LED Alarm Clock Black with Red Numbers OE66AC US $100.00
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 Waltham Anniversary Clock Elvis Presley 1 US $25.99
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 Waltham Anniversary Clock Elvis Presley 3 US $25.99
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 Waltham Anniversary Clock Dolphins US $25.99
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 Dome Wooden Non Ticking Silent Wall Clock Brown US $49.99
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 Elvis Presley Anniversary Clock Battery Operated NEW US $36.99
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 Karlsson Wall Clock Dome Backwards Black US $70.94
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 GE 194 NH 4w 14v T325 Wedge Base Automotive Bulb x2 US $5.35
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 Bai Design Landmark Pick Me Up Alarm Clock 569LA US $27.99
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 Waltham Angels Anniversary Collectible Dome Clock US $19.50
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 La Crosse Technologies 65905 ELC 12 Solar Analg Wall Clock US $30.23
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 Schneider 12 Traditional Cuckoo Clock 8T 90 9 US $264.60
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 1122 LOVE Convex Love Poem Clock US $49.99
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 IMPERIAL BUTTER DOME US $34.53
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How to Use the GPS Clock
The Global positioning System (GPS) is a US military system primarily intended for global navigation. The system provides highly accurate positioning information for navigation. The GPS system consists of a constellation of 24 orbiting satellites. Each satellite has an on-board atomic clock, which is ideal for providing a highly accurate timing reference.
This article discusses how the GPS clock can be used to provide an accurate timing reference for computers and computer networks. The GPS system is often used for computer timing applications, such as NTP time servers and accurate timing references.
GPS Time
GPS time is continuously broadcast by the GPS system. Time is referenced to UTC (Universal Coordinated Time), which is the same worldwide and does not vary with time zones. GPS timing information can be received with relatively low-cost equipment, such as a GPS receiver and antenna.
The GPS signal is very weak low-power radio signal. The signal has two designated frequencies, L1 and L2. Frequency, L1, is the civilian GPS frequency transmitted at 1575.42 MHz. The signal travels in a straight line and can pass through clouds, glass and plastics but is blocked by objects such as metal and brickwork. The ideal location for a GPS antenna is therefore on rooftop with a good view of the sky. Often, antenna installation on the side of a building or in a window can provide a good enough view of the sky to give adequate results.
GPS Clock
The GPS system provides a free-to-air time synchronisation service; there are no on-going set-up or subscription charges. Many computer systems utilise the GPS clock as an accurate timing reference. Highly accurate NTP server systems use the GPS clock as an external reference to synchronise Network Time Protocol servers. Typically, a GPS receiver can provide timing information to within a few nanoseconds of UTC. The accuracy achieved with a GPS receiver is generally more than required for most computer network timing applications.
GPS Receiver Output
The GPS receiver constantly outputs position and timing information. Generally, information is transmitted to and from the receiver via a RS232 serial interface. Standard GPS interface protocols exist, the most common being NMEA. The NMEA protocol consists of a number of sentences, or character strings, transmitted at 4800 bits per second. Contained within each character string is accurate time and position information. Due to the latencies involved in serial communication, the NMEA sentences are not generally accurate enough to provide a timing reference. Therefore a pulse per second (PPS) output is utilised. A PPS output is an accurate pulse output each second that is aligned to the start of each second. The PPS output can be fed into a control line on the RS232 interface to provide a hardware interrupt input for accurate timing. Often the DCD RS232 line is utilised as a PPS input from the GPS receiver. The PPS output combined with NMEA timing and positioning information provides a highly accurate timing reference for computers.
GPS Antennas
The GPS antenna is a signal amplifier that boosts the GPS signal for transmission along a cable, usually coax, to the receiver. GPS antennas used for timing purposes are generally dome-shaped pole mounting devices for permanent installation in a static location. Typically, the GPS antenna is fairly small in size, measuring less than 900 mm in diameter
GPS Cabling
The cable distance that can be utilised by a GPS antenna and receiver depends on the amplification of the GPS antenna and the quality of coax used in the installation. A typical GPS antenna may have a gain of 35 db. Low-quality coax such as RG58 has an attenuation of 0.64 db/m at 1575 MHz. Therefore, a cable run of 55m can be obtained using RG58 cable. Higher quality coax, such as LMR400, an unaided cable run of 200m can be achieved. However, very high quality coax can be expensive. A good compromise is LMR200 cable, which can be run unaided to 80m. Longer distances can be achieved with the aid of GPS amplifiers, which amplify the GPS signal still further, to increase cable distance.
About the Author
D. Evans develops GPS clock and NTP server synchronization solutions that ensure accurate time on computers and computer networks. David has been involved in the development of dedicated time servers, NTP synchronized digital wall clock systems and atomic clock synchronization products. Click here to find out more about NTP Server and GPS clock solutions.
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