Hello group, On our OATS, located in a big hall, a burglar alarm from the 80ties caused broadband noise 20 -150 Mhz Long lines , bad design etc. This was continuous interference so easy to locate.
Regards, Gert Gremmen ----------------------------------------------------------- == Ce-test, Qualified testing == Consultants in EMC, Electrical safety and Telecommunication Compliance tests for European standards and ce-marking Our Web presence: http://www.cetest.nl -----Oorspronkelijk bericht----- Van: Scott Douglas <[email protected]> Aan: [email protected] <[email protected]> Datum: donderdag 26 maart 1998 23:42 Onderwerp: EMI Site Interference >Hello Group - > >Here's a problem for you all to think about and hopefully help solve. > >I have a room in the corner of my building where I perform EMI pre-scans. >Occasionally throughout the day I have a major interference show up on my >analyzer. It does not come from the EUT. This is broadband, from 30 MHz to >1 GHz, at levels up to 70 or 80 dBuv. It is not like a flat carrier but >rather more like PWM driven motor noise. It lasts from 15 seconds to 1 >minute in duration. Then ambient returns to normal. > >We are a typical ITE manufacture. Our Genrad tester, wave solder, air >compressors, motor generators, air conditioners, plumbing waste pumps do >not appear to be the cause although none have been absolutely ruled out. >The frequency and duration would seem to eliminate them however. > >We have swamp on one side, the interstate highway on another, fields on >the third and the town on the last side. The only potential source I can >find is a medical clinic about 350 meters away from us. They are the >nearest building (the next being twice that far) and have an X-ray >machine. Yesterday I went there at lunch and asked was the X-ray in use >that day and they said yes but could not tell me a specific time that it >was used. > >A software engineer here tells me that he has experienced radio problems >in the parking lot outside my corner of the building. When he parks in a >certain spot, his FM radio (the entire band) gets wiped out by a >zhhzhhzhhh kind of noise. Move the car several feet any direction the >problem goes away. This closely resembles what I see on the analyzer. Our >analog guru suggests it is not the x-ray system as x-rays only last a few >seconds. A one minute x-ray would burn you up he says. > >I never noticed this interference in another corner room of my building >diagonally opposite my present location nor have I noticed the FM radio >problem myself. > >Questions: >1. What are the possible sources of such interference? >2. Is the problem radiated or conducted? I suspect radiated as the signal >goes away when you disconnect the antenna from the analyzer. >4. Why does this problem show up in only a small specific location on our >property? >4. What are the potential solutions? > >I will be happy to answer any other questions you think of (if I can) and >I look forward to the interesting comments I will receive from you all. >Thanks in advance. > >Scott Douglas >[email protected] > >
