XTS DVR72XX-V User Manual page 134

network, analog communication, digital communication, cable TV and satellite antenna. For all
the input port, especially those from the outdoor, you need to install the signal lightning arrester.
Antenna feed cable lightning arrester: It is suitable for antenna system of the transmitter or the
device system to receive the wireless signal. It uses the serial connection too.
Please note, when you select the lighting arrester, please pay attention to the port type and the
earthing reliability. In some important environment, you need to use special shielded cable. Do not
parallel connect the thunder proof ground cable with the ground cable of the lightning rod. Please
make sure they are far enough and grounded respectively.
2. The earthing modes
We all know the earthing is the most complicated technology in the electromagnetism compatibility
design since there is no systematic theory or module. The earthing has many modes, but the
selection depends on the system structure and performance. The following are some successfully
experience from our past work.
One-point ground: In the following figure you can see there is a one-point ground. This connection
provides common port to allow signal to be transmitted in many circuits. If there is no common port,
the error signal transmission occurred. In the one-point ground mode, each circuit is just grounded
only and they are connected at the same port. Since there is only one common port, there is no
circuit and so, there is no interference.
Multiple-point ground: In the following figure, you can see the internal circuit uses the chassis as
the common point. While at the same time, all devices chassis use the earthing as the common port.
In this connection, the ground structure can provide the lower ground resistance because when there
are multiple-point grounds; each ground cable is as short as possible. And the parallel cable
connection can reduce the total conductance of the ground conductor. In the high-frequency circuit,
you need to use the multiple-point ground mode and each cable needs to connect to the ground. The
length shall be less than the 1/20 of the signal wavelength.
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