Setting The Cable Length For The Gps System; Connecting Your Gigastor To A Gps System - Network Instruments GigaStor User Manual

Setting the cable length for the GPS System

For GigaStor probes with the Gen2 card, you must define the length of cable between the GPS System and the
GigaStor probe. Adjustments are made to the timings based on cable length.
1. On the GigaStor probe, choose Start > Control Panel > Device Manager > Network Instruments Capture
Adapters > Network Instruments Capture Adapter. Right-click and choose Properties.
2. Click the Advanced Settings tab. Select your GPS Cable Length. This is the cable length from the GPS
Synchronization System to your GigaStor probe. It is not the cable length for the GPS antenna. Click OK.
Your GigaStor probe will now use GPS accurate timing for its captures.

Connecting your GigaStor to a GPS System

GPS is typically thought of as identifying location, but it also uses 24 satellites with four atomic clocks to
accurately identify time, timing, and time differentials.
If you require extreme timing granularity and accuracy, then using the GPS Synchronization System provides
accurate timestamps for up to 15 GigaStor probes.
Most network teams rely on Network Time Protocol (NTP) to synchronize the clocks on all the devices connected
to their network to International Atomic Time. Because of network latency and hardware issues, NTP is typically
accurate to only within 30 milliseconds. Even in the best cases, NTP accuracy is only within 10 milliseconds.
Using the GPS Synchronization System once a second the device calibrates the oscillating crystals on the 10
Gigabit Gen2 capture card to ensure timing accuracy within 150 nanoseconds.
There is no calibration or manual synchronizing that you need to do. Calibration occurs at the factory, and if the
antenna can receive GPS signals, there is no synchronizing that needs to occur, as it happens automatically.
Figure 21: GPS Synchronization System
To install the GPS Synchronization System two things must be done. First, the hardware and antenna must be
installed. Second, the Gen2 capture card in the GigaStor must be configured.
1. Install the antenna on a 1² OD marine pipe or 3/4² ID pipe, with 14 threads per inch. The antenna should be
on your building's roof with a clear view of the sky in all directions. This ensures the antenna can see the
maximum number of satellites available. Although an antenna mounted on a window ledge may receive
a signal, it cannot guarantee good signal reception. See the documentation included with the antenna for
specifics.
Allow for the cable to maintain a "drip-loop" to prevent water intrusion and to allow for flex on the antenna
to cable connector. Be careful not to damage the cable. Take care to avoid sharp bends or kinks in the
cable, hot surfaces (for example, exhaust manifolds or stacks), rotating or reciprocating equipment, sharp or
80 | GigaStor™ (pub. 25.Apr.2014)