From: [email protected] Subject: Re: Doubt on Measuring with Spectrum Analyser Date: Tue, 22 Sep 1998 15:28:56 -0800 To: EMC-PSTC <[email protected]>, Muriel Bittencourt de Liz <[email protected]>
> From: Muriel Bittencourt de Liz <[email protected]> > Subject: Doubt on Measuring with Spectrum Analyser > Date: Tue, 22 Sep 1998 17:35:05 -0300 > To: Lista de EMC da IEEE <[email protected]> > > I'm doing my measurements of conducted emissions using a Spectrum > > Analyser, but my site isn't shielded, i.e. some interferences ( radio > > stations ) appear at the screen of the SA. > > Muriel > This procedure is not a good practice... CONDUCTED EMISSIONS measured on your open field site!!!? Well, I'm sorry; I read right past that and addressed your problem as a radiated one. Fortunately, other posters didn't make that slip and have offered a number of good tips and practices. But let me add a couple of more. It's possible that powerline conducted noise, originating off-site, is obscuring the real data from the EUT. And powerline filters and/or an isolation transformer may reduce your problem adequately. But the noise may be radiated off of nearby powerlines, and is also reaching your site by radiated means as well as conducted. The EUT's powerlines then pick up the radiated energy, and all of your filtering of the site is useless. (This would also be the case for a completely dedicated generator.) My approach has always been to use a powerline filter at the edge of my open field site and to route my filtered power under the ground plane inside steel conduit. But I have always used a shielded enclosure for doing my conducted emission data acquisition. If your EUT is so big that it can't fit into a shielded room, then your can try to find another site, wait for the ambient signal to go away, or try to construct a crude shield structure using grounded, parallel wires strung over the site. Finally (and again, assuming that you have treated the conductive path onto your site), I have heard of active cancellation equipment which can generate a phase shifted image of the offending signal and locally radiate this signal so as to create a limited "null" zone. How big of a null zone, the uniformity of cancellation, the stability ang agility of the cancellation and the cost/complexity of the equipment are all unknown to me. I wonder if any in our group has every tried active cancellation? Ed -------------------------- Ed Price [email protected] Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA. USA 619-505-2780 List-Post: [email protected] Date: 09/23/1998 Time: 09:33:59 -------------------------- --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
