This clause describes calibration of dipoles over a range of frequencies, 698800 MHz to 950 MHz and
1.6 GHz to 32.5 GHz such that the H-field at 10 mm distance from the center of the dipole and the E-field 10 mm out from the end of the dipole is kept constant.
The intent of this procedure is to assure the consistency of the H-and E-field levels a hearing aid is exposed to, during immunity testing, over the specified range of test frequencies.
C.4.1Equipment
Broadband dipoles 698800 MHz to 950 MHz or 1.6 GHz to 32.5 GHz, 3 to 4.5 GHz, and 4.5 to 6GHz
Appropriate test location, i.e., anechoic room or at least a test area large enough so that reflections off of nearby objects do not disturb the test results
Position the H-field probe at 10 mm distance from the top surface of the dipole, which is also fixed in an appropriate fixture (Figure C.1). A gauge block, like that shown in Figure A.4, may be used to accurately set the 10 mm distance.
Make sure that the desired measuring channel of the probe is aligned for maximum reception of the H-field generated by the dipole. This may be accomplished by rotating the probe until the maximum value is located. The H-field probe shall have been calibrated over the frequency range of 800 MHz to 950 MHz or 1.6 GHz to 2.5 GHz using standard calibration techniques.
Adjust the power level of the signal generator at the initial starting frequency such that the desired H-field strength at the 10 mm distance from the center of the dipole is achieved. Setting the field strength to be in the range of category M2 is advised, see Table 4.1 for representative values.
Step the frequency in step increments of ≤ 1%, adjusting the power fed into the dipole such that the desired H-field strength is maintained.
Record the frequency and signal generator setting at each frequency for use during the actual immunity test. A sample calibration chart in is provided in Table C.1, as an example.
Repeat steps using an E-field probe located off the end of the dipole.
If the dipole has a broadband matching section, check that the VSWR is within the specified VSWR over the test band. Tune the dipole or adjust the matching section, if necessary, to achieve better matching.
C.4.3Dipole calibration procedure for wireless devices
Figure C.7—WD dipole calibration procedure
Connect equipment as shown in Figure C.1.
Position the H-field probe at 10 mm distance from the nearest point on the probe element to the top surface (edge) of the dipole as shown in Figure C.3. The desired measuring channel of the probe shall be aligned for maximum reception of the field generated by the dipole. This may be accomplished by rotating the probe until the maximum value is located. The field probe shall have been calibrated at all frequencies in B.2.
Set the power level of the signal generator to a known power, adjusting for return loss input to the dipole at the initial starting frequency, and record the reading from the field probe.
Set the signal generator frequency to all other frequencies given in Table B.1 that meet the insertion loss, VSWR, balance, and gain specifications given in D.5.
Record the frequency and signal generator setting at each frequency for use during the actual immunity test.
Repeat steps using an E-field probe located off the end of the dipole.
If the dipole has a broadband matching section, check that the VSWR is within the specified VSWR over the test band. Tune the dipole or adjust the matching section, if necessary, to achieve better matching.
