| Copyright (c) 2007 Galleon Systems | | | | building with a 180-degree view of the sky if |
| | | | the horizon is not too obscured. |
| This article explains how GPS Time server | | | | |
| Systems achieves exact timing information to | | | | GPS Antenna Types: The GPS antenna is |
| give a highly accurate timing reference for | | | | essentially a signal amplifier. The antenna |
| Network Computer time. | | | | improves the received GPS signals for |
| | | | transmission along a cable to a receiver for |
| GPS System is a navigation system operated by | | | | decoding. A Coax Cable is normally used to |
| the Military but also can be used by the | | | | transfer signal information between the GPS |
| civilian and does not need any subscription. | | | | antenna and receiver. These antennas can be |
| The GPS System is known as an extremely | | | | provided in different shapes and sizes. The |
| accurate global positioning system. Each GPS | | | | general antennas being pole-mounted are dome |
| satellite has an onboard a highly accurate | | | | shaped antennas and small patch type |
| atomic clock, ideal for supplying the correct | | | | antennas. The pole-mounting antenna screws |
| time for computer network time | | | | onto the threaded pole for mounting. Whereas |
| synchronization. | | | | the patch type antenna is a small flat |
| | | | bottomed device ideal for mounting on a |
| GPS Time Servers: The GPS System exist of a | | | | windowsill. |
| constellation of 24 orbiting satellites, each | | | | |
| has a precise atomic clock timing reference | | | | GPS Receivers: GPS Receivers decipher the GPS |
| and covers the entire globe. The exact time | | | | transmission received from the antenna into a |
| information can be continuously broadcast | | | | useable format. NMEA is the most common |
| from each of the satellites. You can receive | | | | protocol used by the GPS receiver. This |
| the broadcast timing information with a | | | | protocol insists a number of sentences which |
| relatively low cost GPS antenna and receiver. | | | | provide a packet on information confirm of |
| | | | time, date and positioning information. The |
| GPS time is transmitted as Universal | | | | NMEA protocol quotes information indicating |
| Coordinated Time (UTC), which is similar to | | | | visible satellites and satellite location. |
| Greenwich Mean Time (GMT). The UTC time is | | | | |
| the same worldwide and does not vary | | | | GPS time servers can use a specific GPS |
| regarding the time zone or daylight saving | | | | timing receiver. These timing receivers have |
| time. UTC is a very accurate atomic time | | | | additional functions to provide a highly |
| standard sustained by atomic clocks located | | | | accurate reference time. The timing receiver |
| in national standards laboratories. UTC has | | | | can also perform an automated survey and |
| consistent seconds distinct by the | | | | compare satellite atomic clocks to check for |
| International Atomic Time (TAI) Institute. | | | | synchronicity. GPS time servers may also use |
| | | | an accurate pulse per second (PPS) output, |
| GPS Radio Transmission: The GPS satellites | | | | which provides a highly accurate reference |
| broadcast information as very low-power radio | | | | trigger for GPS timing, generated by the |
| frequency transmission. There are two | | | | receiver. |
| designated frequency that are used, one for | | | | |
| civilian use coded L1 and the Military use | | | | GPS Antenna Installation: The gain of the |
| coded L2.The civilian L1 frequency is | | | | antenna and the coax is important for the |
| transmitted at 1575MHz. It can easiliy pass | | | | maximum cable distance that can be used by a |
| through plastic and glass but is blocked by | | | | GPS antenna and receiver. An antenna used |
| metal and brick. | | | | with a GPS time server may have 35dB gain. |
| | | | RG58 coax has an attenuation of 0.64dB/m at |
| GPS Antenna Location: The precondition to | | | | 1575MHz. Therefore a cable length of 35 |
| receive transmission from as many satellites | | | | 0.64=55m could be used. Higher quality coax |
| as possible is a good clear view to the sky. | | | | has a much lower attentuation value allowing |
| Ideally a roof mounted antenna is best with a | | | | longer cable runs. Also GPS amplifiers and |
| full 360-degree view of the sky. Conversely, | | | | updown converters can be utilized to increase |
| an antenna can be located on the side of the | | | | the cable length. |