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Precision GPS/GNSS based NTP Network Time Servers
GPS/GNSS Precision Frequency Standards
Networked Frequency Distribution Units with Redundancy
Quality Network Time Displays and clocks
Networked Time Code Distribution Units with Redundancy
Bus Based Plug In Timing Solutions
GPS/GNSS & LF Antenna and protection devices
The most common GPS antenna type used in precision timing applications is known as an Active Antenna. The term “Active” indicates that the antenna requires power to activate it’s internal amplifier circuitry. It is important therefore to appreciate whether the GPS equipment intended for use with the antenna is able to provide the appropriate power to drive it. Usually the DC power required to power the antenna is provided via the central conductor within the coaxial antenna cable.
A simple check with a DC voltmeter can be made at the GPS equipment end to verify that power is available for the antenna. This is typically 5V DC between the centre conductor and the shield. NOTE : Always check the antenna type against the GPS equipment capability.
As the name suggests, a passive antenna has no electrically “Active” components within it, relying purely upon passive filtering components to discern the GPS signal from the ambient. As such, no electrical energy is required to drive internal active amplifiers and the like and thus, such an antenna can be considered SAFE FOR USE in potentially hazardous environments such as Oil, Gas and some military applications.
Without active amplification, the gain of these antenna types is 0dB. This characteristic may also be advantageous where there is high signal and/or high equipment sensitivity.
In situations where the GPS receiving equipment is a long way from the antenna (typically >100m (300ft), a “Head End” or “Long Distance” antenna system can be used. Usually this is a proprietary solution in which a standard GPS antenna is locally mounted on an enclosure containing a GPS decoder (see right).
Such systems receive and separate the GPS signals locally and then re-
The GPS signal processing system, typically a GPS Master Time Clock, will contain a compatible proprietary decoding system enabling the GPS data to be re-
Lightning strikes are typically a combination of pulsed DC with an RF component around 2.2MHz. The first pulse typically averages 18kA with subsequent pulses at about 9kA with an average of three or more pulses in total
A lightning arrestor is designed to shunt the potential high voltage, high energy of a lighting strike, away from the equipment and down to an earth ground point for rapid dissipation.
Since a lighting strike electrical transient is extremely fast and at a potential voltage & energy much greater than that which a GPS receiver is designed to cope with, the effectiveness of an arrestor is broadly determined by the speed at which it can react to such a transient and the levels to which the resultant energy seen by the equipment are minimised.
Broadly speaking, an arrestor is designed to operate at a minimum voltage threshold, within a certain time and with a maximum energy dissipation rating. Both the voltage threshold and the energy dissipation capability depend very much upon a good, low impedance connection to a solid grounding earth.
We recommend a range of Hybrid Arrestors that provide excellent transient performance and service life. Gas discharge type devices are also available in support of legacy installations.
GPS In Line signal amplifiers can be useful when extending antenna cable runs in existing installations.
These units take power from the active GPS antenna line and boost the signal by around 20dB, which is often more than enough to compensate for additional cable extension lengths or where a specific cable type is stipulated.
More information concerning signal loss calculations can be found on page 6 of our installation application note : Click here for application note