EMC FLEX BLOG A site dedicated to Automotive EMC Testing for Electronic Modules

Battery Voltage Dropout

In EMC "dropout" means Battery drops to 0V. FMC1278R3 (CI 260) is an example of various combinations

In EMC "dropout" means Battery drops to 0V. FMC1278R3 (CI 260) is an example of various combinations of such battery voltage dropouts. The problem is that no automotive battery can really drop its output to 0V for say 5 seconds as well as for 50 ms without to blowout a fuse.

 Therefore the only way to simulate correctly a “battery drop to 0V” is to disconnect DUT's B+ line from battery. The test equipment offers such capability to momentarily disconnect the battery during “voltage dropout” simulating a “0V” like condition, practically no current through supply lines to DUT.

This involves the use of PFM200N + VDS200Q + AutoWave to generate the CI 260 type of pulses. PFM200N acts like a very fast switcher disconnecting its output from DUT. So far only FCA (CS.00054) figure it out to ask “open condition” during “0V” battery voltage dropouts. 

In EMC we use the wording “voltage dip” to describe a momentary battery voltage drop (e.g. 4.5V) below minimum supply voltage (e.g. 9V). Obviously in this scenario the Battery B+ line is not disconnected from DUT during the “voltage dip to 4.5V” of 100ms.

 

Christian Rosu Feb 17, 2021

Antenna Factor

19. December 2020 06:25 by Christian in Troubleshooting, Test Equipment, Calibrations
Antenna factor when properly applied  to a field strength meter reading yields the electric fie

Antenna factor when properly applied to a field strength meter reading yields:

  • electric field intensity (V/m)
  • magnetic field intensity (A/m).

The field intensity in the far-field radiation pattern of an antenna:

  • Is proportional to the square root of the effective radiated power. Increasing the effective radiated power four times , the field intensity will be doubled.
  • Is direct proportional to antenna current. If the far-field intensity in the far-field antenna pattern is doubled the antenna current will increase 2 times. 

VSWR (Voltage Standing Wave Ratio)

16. December 2020 09:06 by Christian in EMC/EMI, Test Equipment, Calibrations
For a radio (transmitter or receiver) to deliver power to an antenna, the impedance of the radi

For a radio (transmitter or receiver) to deliver power to an antenna, the impedance of the radio and transmission line must be well matched to the antenna's impedance.

The parameter VSWR is a measure that numerically describes how well the antenna impedance is matched to the radio or transmission line it is connected to.

The voltage component of a standing wave in a uniform transmission line consists of the

  • forward wave (with complex amplitude V_{f}) superimposed on the
  • reflected wave (with complex amplitude V_{r}).

A wave is partly reflected when a transmission line is terminated with other than an impedance equal to its characteristic impedance.

The reflection coefficient \Gamma  can be defined as:

\Gamma  = Vr / Vf

\Gamma  is a complex number that describes both the magnitude and the phase shift of the reflection. The simplest cases with \Gamma  measured at the load are:

  •    {\displaystyle \Gamma =-1}   complete negative reflection, when the line is short-circuited,
  •    \Gamma =0       no reflection,                              when the line is perfectly matched,
  •    {\displaystyle \Gamma =+1}   complete positive reflection,  when the line is open-circuited.

The voltage standing wave ratio is then:

See Tutorials

ANTENNA TYPE

16. December 2020 06:35 by Christian in EMC/EMI, Troubleshooting, Test Equipment
ANTENNA TYPE FREQUENCY RANGE USAGE NOTES LOOP 1 KHz TO 30 MHz Magnetic Field 20 dB dynamic range f
ANTENNAFREQ. RANGEUSAGENOTES
LOOP1 KHz TO 30 MHzMagnetic Field20 dB dynamic range for 1 KHz
ROD1 KHz TO 30 MHzRadiated Emissions41 inches long, uses ground plane and active amplifier
BICONICAL20 MHz to 200 MHzRadiated EmissionsRequired by automotive standards
DIPOLE100 MHz to 1 GHzShielding Effectivenessmore efficient above 400 MHz 
LOG PERIODIC200 MHz to 1 GHzRadiated EmissionsCISPR 25
BICONLOG20 MHz to 1 GHzRadiated EmissionsEuropeean requirements
LOG SPIRAL200 MHz to 10 GHz Shielding EffectivenessCone-shaped. Can't distiguish between horizontal and vertical polarization
HORNabove 1 GHzRE, RI ALSEHighly efficient, directional, can be harmful causing blindness, glaucoma
RIDGED HORN1 GHz to 10 GHzRI ALSEBroadband
HOOD RI ALSEHorn antenna with a metallic hood around it for safety.
HAND-HELD Shielding Effectiveness 
DISCONE  Shielding Effectivenessnot directional
YAGIbelow 100 MHz Shielding Effectiveness 

One-Meter Horizontal Distance Antenna to DUT Radiated Emissions Measurements

The horizontal distance between DUT and Antenna for automotive EMC compliance is 1 meter. For other

The horizontal distance between DUT and Antenna for automotive EMC compliance is 1 meter. For other non-automotive regulatory and standard-based measurements these distances are 3m, 10m, or 30m.

One-meter DUT-to-antenna distance measurements are carried out based on MIL-STD 461 (military), RTCA DO-160 & EUROCAE ED-14 (commercial aircraft), and CISPR 25 (automotive).

CISPR 25 specifies a one-meter antenna distance to be used for radiated emissions from Components/Modules in an Absorber Lined Shielded Enclosure (ALSE).

 

The near field and far field are regions of the electromagnetic field (EM) around an object.
Far-field E (electric) and B (magnetic) field strength decreases as the distance from the source increases, resulting in an inverse-square law for the radiated power intensity of electromagnetic radiation.

Near-field E (electric) and B (magnetic) field strength decrease more rapidly with distance:

  • the radiative field decreases by the inverse-distance squared, resulting in a diminished power in the parts of the electric field by an inverse fourth-power
  • the reactive field by an inverse cubed law, resulting in a diminished power in the parts of the electric field by an inverse sixth-power

The rapid drop in power contained in the near-field ensures that effects due to the near-field essentially vanish a few wavelengths away from the radiating part of the antenna.

dF = (2* D^2)/λ
D= largest dimension of the radiator or diameter of antenna
λ = wavelength of the radio wave
dF = 2*(D/λ)^2
λ = 2* (D/λ)*D
dF >> D
dF >> λ

Near-field and far-field regions for an antenna (diameter or length D) larger than  the wavelength of the radiation it emits, so that ​D⁄λ ≫ 1:

  • Near Field
    R = near field antenna to radiating filed distance
    R = 0.62 * (D^3/λ)^1/2
  • Far Field
    Ro = far field antenna to radiating filed distance
    Ro = 2*(D^2/ λ)