High frequency interference signal of blister equipment

If the interference signal of the high-frequency machine is first received by the dry (main) cable and serialized into it, and then (amplified by the amplifier) ​​and then distributed into the user's TV through the cable, then all the TVs below it will be affected by the high-frequency machine interference. But the actual situation is not the case. Usually, it is only sporadic and "wandering" interference. The proportion of users who are closer to the high-frequency machine is larger, the proportion of users who are slightly farther is smaller, and the users who are 500m away from the high-frequency machine have no complaints. Pass. This proves that the interference signal of the high-frequency machine does not invade the dry (main) line cable first, and then (amplified by the amplifier) ​​propagates to each TV through the cable. Although the intensity of the interference signal radiated by the high-frequency machine is very large, the shielding loss of the dry (main) cable (-12 or -9 physical foam cable) can reach about 80dB, and the interference level intruding into the cable will not be Very high, far less than the TV signal level. The author used the method of spectrum analysis to measure the interference level of the high frequency machine at the end of an 80m long -9 physical bubble cable with copper braided outer conductor. This is a user distribution main line. The high frequency machine is 18m away from the user amplifier and 3m away from the cable. (A wall is separated in the middle), the amplifier is powered off and the household cable is removed (replaced with a 75Ω load resistance) during the measurement. The measured interference level of the intruded high-frequency machine is: the second harmonic < 20dB, and the TV signal level should be It is more than 42~60dB higher than it.