cable news: cable radiation
from：guichao author：admin click： 311 addtime：2017-04-19 18:15:22
it can be said that wire and cable since the invention of the existence of radiation problems.
this is the physical property of the wire, which can be avoided but not eliminated.
people use many ways to avoid it, such as the installation of shielding.
and away from equipment. but the effect is not ideal,
how common mode currents are generated is often a problem for many people.
to understand this problem, first of all, it is clear that the common mode voltage is the root cause of the common mode current,
common mode voltage is the voltage between the cable and the earth (or any other large nearby conductor).
starting from the common mode voltage, it is easy to find the common mode current,
once the cause of a problem is clear, it is not difficult to solve the problem.
there are several reasons for the common mode current on the cable:
common mode current caused by differential mode current leakage,
nor can the signal current 100% return to the source from the return line,
especially in the case of high frequency, the space of various stray parameters for signal current provides third,
even more return paths. this common mode current, although the proportion of small,
however, due to the large area of radiation, radiation is not to be ignored.
common mode current caused by ground noise of circuit board.
the signal ground is the return line of the signal,
there is a voltage between two points on the ground,
these are the high frequency noise voltage, which is the common mode current in the common mode voltage drive cable,
common mode radiation.
a variety of methods to reduce the ground impedance in the design of circuit board,
can be used to reduce the noise on the ground, thereby reducing the common mode voltage.
a recommended method is to set up a "clean"".
the so-called clean ground is no noise on the ground circuit,
so the local potential on the ground wire is almost equal. if the case is a metal case,
connect the piece to the metal cabinet.
common mode current induced by space induced electromagnetic wave in a case.
shielded cable is able to effectively prevent radiation,
there is a layer of shielding. so the cost increases,
moreover, the production steps are increased, the difficulty is increased, but the use is very extensive.