DVR systems DVRxx04HF-A Series - Manual (Page 177)

177
work. The signal lightning arrester has many specifications, and widely used in many
devices such as telephone, 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.
z 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.