Specifications

EMC-CS-2009.1
© Copyright Ford Motor Company – All Rights Reserved Page 93 of 121
February 11, 2010
Annex C (Normative): Mode Tuning Chamber Calibration
C1 Mode Tuning Chamber Calibration (Based on IEC 61000-4-21)
C1.1 Chamber Calibration and Loading Validation
The empty chamber calibration shall be performed prior to the use of the chamber for testing using the procedures of this
Appendix. Prior to each DUT test, a loading validation shall be performed according to the procedures of C2.
All calibrations are antenna specific. Changing antennas prior to a test shall require a new calibration. One loading validation
(outlined in C2) is sufficient at the start of a test with multiple samples. Multiple loading validations are not required in
between tests if the DUT being tested has not been significantly modified to affect its size and shape (i.e. circuit board
alterations).
C1.1.1 Field Uniformity Validation
a) Remove all non-essential equipment from the test chamber including DUTs, simulators, cameras, etc.
b)
Place the transmitting antenna as indicated in the notes of Figure C1 directing it into a corner. The transmitting
antenna shall not be moved during the field uniformity validation. The transmit antenna shall be linearly polarized and
rated for the frequencies being tested. The transmit antenna shall remain in a fixed location for all calibrations and
testing.
c)
Place the receive antenna within the working volume of the chamber defined in the notes of Figure C1. The receive
antenna, probe, or chamber working volume shall not be in the direct path of the transmit antenna. The receive antenna
shall be linearly polarized and rated for the frequencies being tested. The receive antenna shall also be cross polarized
with respect to the transmit antenna.
d)
Place an electric field probe (capable of reading three orthogonal axes) on the perimeter of the chamber working
volume as shown in Figure C1.
e)
At the lowest test frequency (fs = 400 MHz), inject an appropriate amount of RF power, into the transmit antenna. RF
power shall be applied for an adequate dwell time to ensure that the amplitude measuring device and the electric field
probes have time to respond properly. Harmonics of the RF input to the chamber must be at least 15 dB below the
carrier frequency.
f)
Step the tuner through 360° in discrete steps (mode-tuning) so that the amplitude measuring device connected to the
receive antenna (e.g., spectrum analyzer, power meter, etc.) and electric field probes captures the minimum number of
samples required as indicated in Table C1.
An appropriate amount of input power is dependent on the size and material of the test chamber as well as the noise
floor of the electric field probe and amplitude measuring equipment.
g) Record the received power, the field strength for each axis of the electric field probe, and the input power for each step
of the mode tuner. From these values compute the maximum received power, average received power (P
MaxRec
,
P
AveRec
), the maximum field strength for each axis of the electric field probe (EMax x, EMax y, EMax z), and the
average input power (P
Input
) over one tuner rotation. All calculated values shall be in linear units (i.e. Watt, not dBm
and V/m, not dBV/m). Ensure that the power measurement instruments have an equipment noise floor at least 20 dB
below the maximum received power (P
MaxRec
) for proper average data collection.
P
Input
is the forward power averaged over one tuner rotation. The number of samples used to determine P
Input
should be
at least the same number of samples used for chamber calibration. All power measurements are relative to the antenna
terminals (both forward and receive).
h) Repeat steps e) through g) in log spaced frequency steps as indicated in Table C1 until the frequency is at least
4000 MHz (10 fs).
i)
Repeat steps e) through g) for each of the eight probe locations shown in Figure C1 and for eight antenna locations
until 4000 MHz (10 fs). If the receive antenna will be in a specific position during routine testing, the antenna shall be
in one of these positions during the eight runs.
The order of steps f) and h) may be interchanged, i.e., step through all the frequencies at each step of the tuner.