Baluns - Cisco 4116 - EtherFast Switch Design Manual

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Baluns

Most existing analog camera deployments have been installed with coaxial cable, but newer
installations are introducing twisted pair and fiber optic cables. Because twisted pair is easier to
install, a simple solution for new cable deployments is the use of baluns to allow twisted pair cables
to transmit video signals, power, and Pan, Tilt, and Zoom (PTZ) data to analog cameras with
coaxial connectors.
Baluns interconnect different cables that are not compatible, such as coaxial and twisted pair.
Figure 2 shows how a balun can transmit power, video and PTZ data to a camera by using a single
twisted pair cable. When using twisted pair cabling, a balun is required at each end of the cable.
By deploying Cat5 or later twisted pair cable, the same cable infrastructure can support future
deployment of network devices such as wireless access points and IP cameras.
Figure 2. Baluns
A wide variety of baluns are available from third-party manufacturers to support a range of
applications. The example in Figure 2 shows a Cat5 cable, but other baluns can be used to convert
from Cat5 to coaxial. Be aware that baluns are unmanaged devices that introduce another point of
failure and can be difficult to troubleshoot.
Serial Connectivity
In a CCTV environment, PTZ data is transmitted using serial communications. Table 4 shows the
most common serial protocols and some of the relevant characteristics of each:
Table 4. Serial Cables
Specification
Maximum Cable Length
Maximum Data Rate for RS232
Maximum Data Rate for RS422/RS485
(50 m–1,200 m)
Receiver Input Voltage Range
Mode of Operation
RS-232C is a serial communications standard that is used to interface serial devices over cable
lengths of up to 20 meters. RS-232C was originally intended to support modem and printer
applications, but it has been expanded to support other applications. RS-422 communications can
carry data over longer distances and at higher rates and resist noise interference better than RS-
232C.
RS232 RS422
20 m 500 m
20 kb/s
10 Mb/s–200 kbps
+/– 15V –10V to +10V
Single-ended Differential
Design Guide
RS485
1,200 m
10 Mb/s–20 0kbps
–7V to +12V
Differential
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