Radiated/Conducted Emissions for AM bands Emissions OEM Frequency Band NB/BB dBuV Voltage Current CE DCX G1 (LW AM – EU) 0.15 – 0.28 MHz 50 (PK/AV) 30 (PK/AV) 60 (PK,QP) 40 (PK,QP) G2 (MW AM) 0.53 – 1.7 MHz 34 (PK/AV) 6 (PK/AV) 50 (PK,QP) 22 (PK,QP) G3 (SW AM – EU) 5.8 – 6.3 MHz 33 (PK/AV) -1 (PK/AV) 40 (PK,QP) 6 (PK,QP) GM G1 (MW AM) 0.53 – 1.71 MHz 42 (PK) N/A 50 (QP) N/A FORD G1 (MW AM) 0.53 – 1.7 MHz 66 (QP) N/A RE DCX G2 (AM) N/A G2 (AM) N/A GM G1 (MW AM) 0.53 – 1.71 MHz 30 (PK) 24 (QP) FORD G1 (MW AM) 0.53 – 1.7 MHz N/A 30 (QP) Small changes in the configuration of conducted-emission tests can give rise to considerable variations in measurement readings, especially at higher frequencies. Errors introduced by the human factor (planing, geometrical requirements of the test setup), as well as the latitude provided by the standard, are two major causes of poor repeatability in these tests.   Vs [MHz] VBW RBW Step Size Time/Step CEI, CEV, RE ALSE Vs ≤ 2/3 RBW * fm 30 KHz  9/10 kHz  ≤ 5 kHz  > 5 ms     30 KHz 100/120 kHz ≤ 60 kHz > 5 ms  Legend: Vs [MHz] = Sweep speed, fm [Hz] = Modulation Frequency, VBW = Video Bandwidth, RBW = Radio Bandwidth Far Field Emissions 1)      Common-Mode (CM) a)      Noise level mostly unaffected if removing the load, CM currents can return via parasitic currents to their source. b)      CM emissions doubles when doubling the frequency c)       CM emissions are usually much greater than DM emissions d)      For a fixed “r” distance between lines, CM emissions can be reduced  by: i)        Decreasing the CM current level The common mode current is the undesired component of the current and is not necessary for the functional performance of the circuit. They are difficult to predict and their existence depends on the non ideal aspects of the structure such as asymmetries. Emissions from common mode currents are larger than the differential mode currents. ii)       Decreasing the frequency of the CM currents iii)     Decreasing the length of the line   2)      Differential-Mode (DM) a)      Sensitive to the rotation of the cable (harness) b)      DM emissions quadruples when quadrupling the frequency c)       DM emissions are usually much lower than CM emissions d)      DM emissions can be reduced  by: i)        Decreasing the DM current level: (1)    by reducing the peak levels of the functional signals (2)    by decreasing the pulse rate, rise time or fall time The differential mode current is equal in magnitude but opposite in direction at a cross section on the line. This is the desired current that is assumed by the designers of the product. ii)       Decreasing the frequency of the DM currents iii)     Decreasing the length of the line iv)     Decreasing the loop area: (1)    by using dedicated return signal conductor (2)    by  using a gridded ground system (3)    by using multi layer boards Keeping the signal and its return adjacent to each other reduces the loop area and hence the emissions of the differential mode current by a factor of 3 dB or 10 dB. v)      Decreasing the spacing between the conductors of the line (harness) vi)     Changing the orientation of the lines   Noise coupling method: 1.       Radiated coupling - escape completely from the source 2.       Inductive coupling - between cable and cable and it is minimized by the adequate spatial separation and by running cables at right angles to the each other or as nonparallel, as practical cables are also sources of radiation to other equipment. Internal to the equipment, inductive coupling between board’s traces is a common problem.   EMI from rectifiers   The rectifier produces a much higher emission during its switch off operation. The interference effect can be reduced: 1.       by limiting the magnitude of the surge current 2.       by decreasing the slew rate of the negative surge current   EMI from SCRs   High Frequency noise levels are much higher at switch on than at switch off.   EMI from power transistors   The switching time for power transistors is much shorter than for the SCR. The fall time of the collector current is rather short usually in the range of approximately 10 ns to 100 μs depending on the rated power of the transistor. Therefore the EMI produced by the power transistor is much wider than that produced by the SCR.   EMI from the semiconductor equipment   EMI generated by power electronic is often that of a pulse train, since rectification involves repetitive switching from conduction to cut off. The repetition rate is some multiple of the operating frequency depending on the circuit configuration.   Principle of resonance based switching   If a switch in a converter changes its status (from on to off) or vice versa when the voltage across it and/or the current through it is zero at the instant of switching it requires some sort of LC resonance and so they are classified as resonant circuits. Ideally both switch voltage and current should be zero at the instant of switching transient. PWM control can be utilized to provide zero voltage and/or zero current switching.

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