Edwin L. Bronaugh

Helmholtz coils for calibration of probes and sensors: limits of magnetic field accuracy and uniformity

Helmholtz coils have been around us for years, but few people now seem to understand their capabilities. The paper explains the accuracy and field uniformity limits of helmholtz coils for use as a calibration standard for magnetic field probes and sensors. The magnetic field generation accuracy depends on the accuracy with which helmholtz coils are constructed and the accuracy with which the current through them is maintained. The user is shown how to determine the accuracy of the generated magnetic field based on physical measurements of distance or spacing between the coils, their radii, the thicknesses of the windings on each coil and number of turns. Ways to estimate the maximum usable frequency and minimum space needed around them are given. Procedures are given so that the user may determine the field uniformity versus volume around the center point of the set of coils, and thus determine the coil characteristics needed to calibrate a particular probe or sensor.

EUT directivity and other uncertainty considerations for GHz-range use of TEM waveguides

Over the past several years, there has been an increasing trend to identify and minimize measurement uncertainties in most types of EMC testing. This paper describes various uncertainty influence quantities that may affect direct voltage-based or correlated E-field radiated emissions tests in most TEM waveguides, and specifically in the GTEM cell. Most TEM-waveguide emissions testing is based on the measurement of EUT total radiated power. To clarify directivity and EUT loading influences, total radiated power and field strengths measured from canonical loop antenna and slotted and raised-lid box EUTs in GTEM cells in the 30-2000 MHz frequency range is presented. Measured results from various GTEM multi-position conversion-to-free-space or -OATS schemes are compared. The intent is to describe an analysis framework and raise awareness so that operators can begin to recognize and minimize uncertainty sources, and to contribute to better understanding of correlation effects in GTEM.

Simplifying EMI immunity (susceptibility) tests in TEM cells

The author addresses two problems encountered in EMI (electromagnetic interference) immunity tests of printed circuit boards and other small electronic assemblies in TEM (transverse electromagnetic) cells. One time-consuming activity in these tests is the repetitive repositioning and testing of the device under test (DUT) to assure that all likely EMI coupling orientations have been tried. The other problem is spurious results arising from undesired induction of the test signal on the wires which service the DUT. It is shown that the time required to repeatedly test the DUT in different orientations may be reduced by mounting it on a dielectric rotary shaft on its ortho-axis. The ortho-axis makes an angle of 54.7 degrees to the edges and centerlines of each face of the DUT; this angle is the ortho-angle. A single 360 degrees rotation of the DUT around the ortho-axis exposes all its orientations to the TEM-cell fields. The DUT service wires may be brought out of the TEM cell along the ortho-axis and shielded by a metal tube around the axis. Care must be taken in the design of the DUT service wiring to avoid coupling to the H-field. In particular, current loops in the wiring must be avoided or made as small as possible.<<ETX>>

Estimating EMC measurement uncertainty using logarithmic terms (dB)

This paper gives background for understanding the use of logarithmic data for making statistical calculations to estimate measurement uncertainties in EMC measurements. When multiplicative data are used, the lognormal distribution is the correct distribution to apply. The distribution is transformed by Y=LnX, creating a normal distribution for logarithmic data and the work is done in logarithmic terms, i.e., dB. Only when additive data are used, should the normal (sometimes called Gaussian) distribution be applied. A correct method using logarithmic (multiplicative) data is shown, and some common errors in using linear (additive) data are mentioned.

Intentional emitters above 2400 MHz: how best to measure the transmitted signal level for FCC Part 15 compliance

This paper investigates the commonly used methods for measurement of the intentional signal levels emitted by Part 15 radio frequency (RF) devices operating above 2400 MHz, and that have built-in antennas that are soldered directly to a printed circuit (PC) board and are not normally removable. In this paper, we look at what the Federal Communication Commission (FCC) rules really require, and the extent of the possible errors involved in the different ways of measuring the intentional signal fundamental and harmonics. The reliability of the measurements for preventing interference to licensed radio services maybe improved by making radiated emission measurements whenever possible to compare the maximum field strengths to the FCC field-strength limits; determine the transmitter output from the EIRP at the higher frequencies; and, apply the FCC guidance on measurements for direct sequence spread spectrum systems only to direct sequence spread spectrum transmitters.

Rod Antennas for High-Strength Radiated Susceptibility Tests from VLF to HF

The Low Frequency RS03 Rod Antenna, used in conjunction with a suitable signal source, will produce electric fields greater than 50 volts per metre at a distance of one metre from the radiating element over the frequency range 10 kHz to 2 MHz. Less than 100 watts is required to produce the 50 V/m E-Fields. Later developments covering the range of frequencies from 2 MHz to 30 MHz are also reported. The antennas consist of four components-the base, counterpoise, radiating element, and top hat.

ELF E-Field Meter for In-Vitro Field Strength Measurements for Bio-Effects Research

A field strength meter which may be used to measure the levels of high-strength electric fields invitro in cell cultures is described. The meter measures field strengths from 1 kV/m to 100 kV/m in the 30 Hz to 300 Hz frequency range. The natural extension of the measurement frequency range into the UHF region is discussed. Applications and needed future experimental work are discussed.