Coaxial Surge Protection Overview
Protection For Radio Communication Equipment
Radio communication equipment deployed in fixed, nomadic or mobile applications is especially vulnerable to lightning strikes because of their application in exposed areas. The most common disruption to service continuity result from transient surges originating from direct lightning strikes to the antenna pole, surrounding ground system or induced onto connections between these two areas.
Radio equipment utilized in CDMA, GSM/UMTS, WiMAX or TETRA base stations, must consider this risk in order to insure uninterrupted service. CITEL offers three specific surge protection technologies for Radio Frequency (RF) communication lines that are individually suited for the different operational requirements of each system.
RF Surge Protection Technology
Gas Tube DC Pass Protection
Gas Discharge Tube (GDT) DC Pass Protection is the only surge protection component usable on very high frequency transmission (up to 6 GHz) due to its very low capacitance. In a GDT based coaxial surge protector, the GDT is connected in parallel between the central conductor and the external shield. The device operates when its sparkover voltage is reached, during an overvoltage condition and the line is briefly shorted (arc voltage) and diverted away from sensitive equipment. The sparkover voltage depends on the rise front of the overvoltage. The higher the dV/dt of the overvoltage, the higher the sparkover voltage of the surge protector. When the overvoltage disappears, the gas discharge tube returns to its normal passive, highly insulated state and is ready to operate again.
The GDT is held in a specially designed holder that maximizes conduction during large surge events and still very easily removed if maintenance is required due to an end of life scenario. The P8AX Series can be used on coaxial lines running DC voltages up to -/+ 48V DC.
DC Pass - CXF60 series
DC Blocked - CNP-DCB series
Hybrid DC Pass Protection is an association of filtering components and a heavy duty gas discharge tube (GDT). This design provides an excellent low residual let through voltage for low frequency disturbances due to electrical transients and still provides a high surge discharge current capability.
Quarter Wave DC Blocked Protection
Quarter Wave DC Blocked Protection is an active band pass filter. It has no active components. Rather the body and corresponding stub are tuned to one quarter of the desired wave length. This allows only a specific frequency band to pass through the unit. Since lightning operates only on a very small spectrum, from a few hundred kHz to a few MHz, it and all other frequency's are short-circuited to ground. The PRC technology can be selected for a very narrow band or wide band depending on the application. The only limitation for surge current is the associated connector type. Typically, a 7/16 Din connector can handle 100kA 8/20us while an N-type connector can handle up to 50kA 8/20us.
UL497E – Protectors for Antenna Lead-in Conductors
Parameters for Selecting a Coaxial Surge Protector
The information required to properly select a surge protector for your application is the following:
- Frequency Range
- Line Voltage
- Connector Type
- Gender Type
The proper installation of a coaxial surge protector is largely dependent on its connection to a low impedance grounding system. The following rules must be strictly observed:
- Equipotential Grounding System: All the bonding conductors of the installation must be interconnected to each other and connected back to the grounding system.
- Low Impedance Connection: The coaxial surge protector needs to have a low resistance connection to the Ground System.