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

STANDARDS AND GUIDELINES FOR COMMUNICATION SITES RF COMPONENTS PROTECTION
The shorted stub inductor device is frequency-sensitive, therefore it must be selected for the specific
frequency band in use. Different bands multiplexed on the same transmission line will not work with
band-limiting devices such as the shorted stub inductor. The shorted stub inductor device is
mechanically large compared to other gas protector/reactive filter lightning surge protector devices in
common use. There could quickly develop an installation space problem if a number of transmission
lines are protected by individual shorted stub inductor devices at the common facility cable entrance
port. The shorted inductor type device differs somewhat from the shorted stub inductor type device in
that the shorted inductor type device incorporates a helical wound shorted inductor. These devices
typically exhibit an open DC circuit through the device and have a much larger bandpass than a shorted
stub inductor device.
All coaxial RF surge suppression devices shall exhibit an open DC circuit through the device
(unprotected port center pin to protected port center pin), except those specifically designed to pass DC
for CCTV, tower top amplifiers and GPS installations as described in this chapter and “GPS Receiver
Protection” on page 7-44. The input and output ports shall not be directly connected and may have a
capacitive or reactive network installed within the device to permit the RF energy to pass. The
unprotected port and the protected port shall be clearly marked on the device.
Typical RF characteristics for RF SPD are voltage standing wave ratio (VSWR) of less than or equal to
1.1:1 (return loss of -26.4dB) and an insertion loss of less than or equal to 0.1 dB over the network
operating frequency range. These devices are also specified to handle surge currents from 10-20kA 8/20
µs waveform. Selection of the proper SPD for RF transmission lines depends on the specific
application.
1 2.000 V/D
-2.0000 ms 23.0000 ms 40.0000 ms
5.00 ms/DIV
REALTIME
VMAX ( 1 ) 5.62500 V VMIN ( 1 ) -1.81250 V
FIGURE 7-20 QUARTER-WAVE STUB, OSCILLOSCOPE SET AT 2V/DIV V AND 5 µS/DIV H, 8X20µS/
3KA
68P81089E50-B 9/1/05 7-39