GPS signals are weak and often impractical in urban environments due to limited visibility of the sky, and constraints of roof-top access and long GPS antenna cable runs. Skylight is a result of Spectracom’s expertise in GPS reception and applications for precision timing. Proprietary alogorithms use a combination of high sensitivity receivers, accurate internal oscillators and other techniques to extract the GPS on-time point to sub-microsecond accuracy even in areas with somewhat limited GPS reception.
Skylight does not work everywhere. A GPS signal above about 30 dBc/N0 at the antenna panel is required. Subterranean and other radio-isolated locations will still need to be synchronized using other techniques (such as over a network via a PTP master-slave combination) versus by GPS directly. However, exterior walls or walls across from a window in above ground floors of a building are likely candidates for Skylight. Even urban canyon situations can be considered as neighboring buildings can often redirect signals to the antenna panel that contain useful timing information for the Skylight system. And the signal does not have to be available 24/7. By using a precise stable oscillator and our proprietary disciplining algorithms, Skylight needs the GPS signal for only a few hours a day. Often the RF noise is reduced at night which can allow Skylight to maintain legally traceable time even if signal acquisition is subpar during the day.
Simple Set-up
The indoor antenna panel can be mounted facing towards or away from the wall it is mounted on, or the decorative cover can be removed and it can be placed on top of a server rack, or even above ceiling tiles. It then gets connected via a RG-58 coaxial cable to a Spectracom SecureSync® modular time and frequency reference system up to 200 feet (60 meters) away. The cable length can be extending using an in-line amplifier to 600 feet (185 meters). The SecureSync is a 1RU NTP time server, PTP grandmaster, and provider of virtually any other network or physical synchronization signal. You can configure the SecureSync at time of order to suit your application for precision timing including the quality of internal oscillator and the ability to sync to GLONASS satellites in addition to, or in lieu of GPS.
Installation Tips
Whether a particular location is suitable for indoor GPS via Skylight depends on several factors. The antenna should be located as close to an exterior wall as possible. It is not necessary for the antenna to be located at a window because in many cases walls attenuate the signal less than the coatings found on modern high efficiency windows. The presence of structures surrounding a building can also affect the availability of signals in a positive or negative way. In general, the higher in the building the antenna is located, the better. Placement near a window can be advantageous if the window is free of coatings and other window coverings or blinds that will block the signal.
