At 10:36 AM 6/12/97 -0700, Randy Flanders wrote: > >Richard and Robert: > >I agree with Richard, although I would recommend the opposite. I would Test >at 10 meters, and bring the antenna in to 3 meters if I come across >frequencies where ambients are interfering. This provides most data at the >specified test distance, while allowing for correction of signals that >appear near ambients. > >Randy Flinders >EMC Test Engineer >Emulex Network Systems > ----------
Richard, Robert, and Randy: Randy's procedure is the procedure followed by the company I am presently employed by. In the presence of a high ambient, there is practically very little you can do otherwise. When a measurement is made at 10m, the turn table and antenna height are positioned for a maximum reading. This means that the signal has a certain level of directionality. The problem is that 10.5 dB extrapolation factor from 10 to 3 metres does not factor into account the level of directionality from the EUT. This gives an unfair advantage to testing at 3m. The extrapolation factor adds 10.5 dB to the limit. The EUT due to it's non-isotropic radiation may only result in a 6 dB raise in signal strength when remeasured at 3m. In this case, this method basically adds 4.5 dB more margin for the EUT. Essentially you could end up with a passing 3m set of results and a failing 10m set of results. This could be a problem for some companies and some test labs. Any comments or suggestions are certainly welcome. Scott D. Drysdale EMC Technician KTL-Certelcom Laboratories Inc. Ottawa, Canada --------------------------------------------------------------- The opinions expressed in this message are exclusively mine and do not necessarily reflect those of KTL-Certelecom.
