standards and guidelines for communication sites - Radio And ...

RF COMPONENTS PROTECTION CHAPTER 7: SURGE PROTECTIVE DEVICES
CAUTION
The manufacturer must verify that the SPD is suitable for use on high bandwidth data
circuits in excess of 1.54 Mbs.
CAUTION
SPDs using SAD technology may develop an artificial diode bias when subjected to
strong RF fields that may be experienced at AM, FM or TV broadcast sites. This bias
may cause data circuit errors.
7.5.3 FIBER OPTIC CABLES
An intrinsic benefit of fiberglass (fiber optic) telephone lines is that they offer excellent isolation from
lightning induced ground potential rise, line-induced lightning strikes, RF, and electrical noise coupling.
The “fiber” telephone/data line is far from perfect as it can melt when subjected to high energy strikes or
fire. No primary SPD is required for fiber circuits entering a building, shelter or equipment area;
however, any metallic shield, jacket or drain conductor shall be bonded to the MGB. A secondary SPD
may be installed on the equipment end of copper circuit conductors originating at a fiber optic network
interface unit (NIU) in areas where the level of lightning exposure is high.
Suitable surge suppression devices offering primary and secondary protection are available from several
surge suppression device manufacturers. Devices shall be selected based on the specific application and
requirements specified above.
7.6 RF COMPONENTS PROTECTION
RF transmission lines from the antenna structure to the shelter or building shall be grounded (earthed)
as described in Chapter 4, “External Grounding (Earthing).” Upon entering the shelter or building, all
RF transmission lines (including sample port (test) and unused spares) shall route through coaxial RFtype
SPDs. The coaxial RF devices shall be bonded to the single point ground window as described in
Chapter 5, “Internal Grounding (Earthing).” The SPD shall be located within the shelter, room or
equipment area and shall be a maximum distance of 610 mm (2 ft.) from the transmission line entrance
point into the shelter, room or equipment area as shown in Figure 7-22 on page 7-42. Some RF surge
protection products can be installed at or within the entry port; this is the most desirable location to
install coaxial cable SPDs if the entry port is located in the wall of the shelter, equipment room or area.
If the equipment room or area is located within a larger building (such as a high rise structure), it is
desired that the SPDs are installed and grounded at the coaxial entry point into the structure. In this
application, the transmission lines shall also have SPD installed and shall be grounded at the point
where they enter the equipment room(s) or area(s).
NOTE: SPDs are required to be installed at the building entry point to reduce the radiated RF energy generated
by a lightning strike.
7-36 68P81089E50-B 9/1/05