In order to understand what the OATS is capable of, it is best that users comprehend the principles behind the sites operation. The subject matter of OATS theory is presented and covers the types of EMI, phase centre PC variation of antenna, near and far field boundaries, antenna factors AF , ground reference planes, multipath propagation, wave reflections and statistical uncertainties. Consideration is also given to environmental sustainability and ethical responsibilities.
The practicality of the site is discussed in the context of Australian standards. The standards are looked at individually for their contribution in the overall development of the site.
The OATS is then assessed for indicative parameters such as physical site influences, equipment limitations, spectral allocation and legal responsibilities. The site validation procedure developed for this project is presented in detail. This includes the combination of several site modifications and the methodology behind each configuration. The determination of test equipment correction factors CF and the correct implementation is introduced. First we had to determine which type of facility of the two kinds available was best to perform the radiated and conducted emissions testing in our particular circumstances.
The SAC, though extremely efficient, had cost estimates for a ten-meter chamber reaching beyond several million dollars. The OATS facility, with a cost under one million dollars including instrumentation was much more financially feasible. By definition, an OATS facility is not actually a building. The ideal OATS is a flat piece of land, free of obstructions, away from any and all external signals, with a perfectly reflective surface.
But because our test site would be in an industrial complex next to a small airport, a structure would have to be placed around the reflective ground plane of the OATS, making it less open than the ideal but still approximating ideal conditions.
This abbreviation was used throughout the project to minimize confusion. It is not common to construct a building using non-metallic material. Our challenge became striking a balance between keeping the area free of reflective materials for EMC testing and making the framework structurally sound. Some of the same issues that gave us a challenge at the outside labs came into play in our design and build. Ambient signals are abundant near an airport within a city near a larger metropolitan area.
Broadcast TV, AM and FM radio, wireless towers, family radio, air traffic control, emergency dispatchers and now, broadband high definition TV HDTV , are consuming larger portions of the RF spectrum and can readily be detected by antenna at our location.
Due to these ambient emissions, a careful site survey was conducted prior to site selection, wherein we measured the direction and amplitude of the ambient signal spectrum. After reviewing the data, we positioned the building such that, during testing, the receive antenna would be facing away from the highest ambient source s , attenuating those signals as much as possible.
We also knew wires and conduits were going to be a problem in testing. As we explain below, this was easier said than done. Our customers expect conditioned, uninterrupted power with ratings up to 8 MVA for multi-module systems, and up to 1. We chose 1. The building size and specifications were based on these requirements. As we proceeded, we had to deal with a laundry list of issues and considerations, among which included:.
Best Practices Note: To make code approval a smoother process, talk to the local inspector and discuss the goals of your project.
Getting input on the front end will ensure that issues are addressed early in the design and build, and they can give you expert insight. They will also appreciate not being blindsided during inspection. Likewise, assume that the architect and turntable manufacturers will not be familiar with EMC testing, and educate them at the outset to ensure that their deliverables are in line with your needs and expectations.
Essentially, it was our task to ensure that the OATS we had spent so much time developing, from design to construction, met the standard requirements in order to actually be utilized. Using Log-Periodic and Biconical antennas, we performed a volumetric test on the ten-meter area between the turntable and the future location of the receive antenna mast. The ideal or reference site is nothing but a perfectly conducting large plane The radiated power is determined by the antenna' s current and the over level ground.
Equation I may therefore also be written as ground plane. The site is an elliptical, open, leveled area, with major and The received power of a matched 50 n lossless antenna is the minor axes of 2R and R j , respectively. The distance between product of the power density, Pd, of the incident ield and the the antenna and the equipment under test EUT is R. The standard site calibration is based on the measurement of the insertion loss between transmitting and receiving antennas on a large, lat, and unobstructed conducting ground plane.
As speciied in clause 5. One antenna is set to be at a ixed height e. The maximum response between the two antennas is recorded. The conducting ground plane is there to ensure the repeatability of the calibration measurements. This tutorial is organized as follows. The ield strength at a distance d over perfectly conducting lat ground is also given in this section.
The deinition of the normalized site attenuation is presented in Section 3. The theoretical normalized-site-attenuation calculations mentioned in the standards are included in Section 4, Figure l. Section 6 table. The basic circuit representation of a transmitting antenna consists of a complex impedance, ZA , connected across a voltage source with an intenal impedance Zs. The input impedance, ZA , of the antenna consists Figure 2. Here, waves. The normalized site attenuation is deined as the ratio of the power input of a matched, balanced, lossless, tuned dipole radiator to that at the output of a similarly matched, balanced, lossless, tuned dipole receiving antenna, for speciied polarization, separation, and heights above a lat electromagnetically relecting surface [I].
It is a measure of the transmission path loss between Figure 3. Figure 4. Re Finally, the nonalized site attenuation is calculated rom In these charts, hmx is the maximum receiving antenna height where E Dmx is recorded. Nonalized site 00 40 attenuation values as a unction of requency for both vertical and Fqueny [Mz] horizontal polarizations above perfectly conducting and lossy ground are shown. Figure 6 shows the ront panel of the standalone Figure 5.
For a free-space environment and ininitely small lossy ground, the dashed line is for PEe ground. I --o Table I lists free-space normalized site attenuation values at some requencies computed rom Equations 18 , 19 , and 20 in free space. I y- As observed, using Equation 20 instead of Equation 19 introduces -. This error is less than 0. Therefore, the free-space Figure 6. The front panel of the normalized site attenuation calculator. NSA Measurements Table 1. To be sure, normalized site 40 9.
These require a maximum of 20 separate measurements 80 3. The irst Vr reading belongs to the case where the two antennas are removed, and coaxial cables are directly connected to each other antennas and 20 system , normalized site attenuation can be via an adapter.
For both of these measurements, the height of the signal source is kept constant. Note that VDirect includes cable [ Mz ]. Also, the transmitting and receiving antennas should 3. Record the maximum signal level. This value is VSite in be aligned with the antennas' elements parallel to each other and Equation Furthermore, the lower tip of the antenna should be at a distance greater than 25 cm rom the 4.
Disconnect the transmitting and receiving cables rom loor, which may require the center of the antenna to be slightly their antennas. Directly connect these cables with a higher than I m for the lowest height measurement.
0コメント