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Radio Frequency Interference Measurement System

IP.com Disclosure Number: IPCOM000035422D
Original Publication Date: 1989-Jul-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 4 page(s) / 65K

Publishing Venue

IBM

Related People

Barfield, DJ: AUTHOR [+5]

Abstract

Radio frequency interference (RFI) is emitted by electronic computer equipment. Many countries have legal requirements limiting the level of RFI from computers and associated equipment. The function of a development laboratory RFI facility is to measure these levels. The method described here is a system in which equipment under test (EUT) undergoes pre-cursor tests in a semi Anechoic Chamber to rapidly characterize RFI emissions. The EUT is then transferred to a Free Field Site, which meets Test Standard requirements, where data from the first tests is used to measure accurately the frequency and amplitude of the RFI. The system elements comprise of electronic, pneumatic, software, operator and a special test-building to enable faster throughput and more thorough testing.

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Radio Frequency Interference Measurement System

Radio frequency interference (RFI) is emitted by electronic computer equipment. Many countries have legal requirements limiting the level of RFI from computers and associated equipment. The function of a development laboratory RFI facility is to measure these levels. The method described here is a system in which equipment under test (EUT) undergoes pre-cursor tests in a semi Anechoic Chamber to rapidly characterize RFI emissions. The EUT is then transferred to a Free Field Site, which meets Test Standard requirements, where data from the first tests is used to measure accurately the frequency and amplitude of the RFI. The system elements comprise of electronic, pneumatic, software, operator and a special test-building to enable faster throughput and more thorough testing.

Two facilities are used for measuring RFI; the free field and the semi anechoic chamber. The free field 1 (Fig. 1) is the ground floor of a building which has an earthed conducting plane 3 at ground level. The area is covered by non- metallic building materials 2. A turntable 4 in the middle of the building 2 is used to rotate the equipment under test 5 (EUT). Any RFI from the equipment is only reflected from the ground plane and radiates as if it were located in the open or a free field. An antenna 6 is attached to a mast 7 which, in turn, is mounted on a trolley 8. The antenna 6 can be moved up and down the mast 7; it can be rotated to change its polarity, and it can be moved towards or away from the turntable. The antenna and turntable are remotely controlled from the basement
9.

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The chamber 10 is located in the basement, and has its walls and ceiling lined with RF absorber material 11, which reduces internal reflections of radio frequencies. It contains a similar antenna 12 to the antenna and mast 7 in the free field, except that it does not have a remotely controllable trolley. The chamber's turntable is also remotely controlled from the basement 9. Chamber 10, unlike the free field 1, is shielded from radio frequency radiations, such as radio stations, radar and other ambients. But unlike the free field, it suffers from internal reflections, mainly at low frequencies due to limitations of the absorber
11. The chamber is, therefore, only used to find out which frequencies are potential problems and the data obtained is used to conduct a free field test, where compliance to various standards is judged. Chamber Test System Hardware

An IBM PC AT 14 running PC APL2 under DOS 3.1 is at the center of the test system which uses an IEEE 488 bus 15 to communicate with a Microlink interface 16. The Microlink 16 is used to relay commands from the PC to a Festo pneumatic controller 17, which, in turn, controls air supplies to the chamber turntable air motor 18 and antenna polarity change pistons 19. An optical encoder 20 sends turntable position information back to the Microlink 16 which is then available...