QUOTE: "And I don't think that 92dBuV/m is a high field strength to be emitted by a PC placed nearby, or for a non-compliant laptop at 10 metres."
You may not think so, but I am sorry, the numbers just don't add up. 92 dBuV/m at 10 meters implies an effective radiated power of 5.3 mW. Consider that the source is not an intentional antenna. It will have no more directivity than a dipole and its efficiency will be much less since it isn't matched to the source. If we simply assume no gain (meaning matching losses just offset directivity) , that means 5.3 mW of rf power are emitted from the EUT or its attached cables. If one makes the reasonable assumption that it is common mode rf current which is radiating, then the potential associated with rf power will be a small number of millivolts (in the frequency domain). This in turn implies a significant fraction of an Ampere of common mode rf current. A highly unlikely situation! Once again, with an impossible conclusion, either the assumption or the logic must be wrong. You can choose to disbelieve, but please point out where the logic has gone awry. You have several times cited Mr. Woodgate for non-constructive criticism. Now I am asking you, don't give more hearsay: explain where my physics is incorrect. We are engineers here, not pollsters. And if you are saying that specification level compliance at 10 meters can scale up to 92 dBuV/m nearby, that is either false or misleading depending on the frequency range. At the low end, say 30 MHz, the area subtended by position near the offending PC isn't large enough to efficiently radiate or couple the field (the wavelength is 10 meters, and the other gentleman's antenna factor calculation assumed a tuned dipole antenna in order to get a small antenna factor). So the field will not scale up as per your prediction, and the pickup mechanism will be nowhere near the antenna factor that gentleman calculated. In fact at 30 MHz your antenna factor will be on the order of 20 dB or worse (assuming the mutual coupling length to be 1 m). At the high end (near 1 GHz) you could be in the far field in close and the field could scale up to a value of 92 dBuV/m, but the antenna factor of a matched tuned dipole at 1 GHz is 26 dB so the potential from that perfect antenna is 92 dBuV/m - 26 dB/m = 66 dBuV or 2 mV. If you consider that any signal with information content carried by 2 mV is shielded, the issue becomes, once again, a non-problem. on 1/6/02 10:43 AM, [email protected] at [email protected] wrote: Snip: And I don't think that 92dBuV/m is a high field strength to be emitted by a PC placed nearby, or for a non-compliant laptop at 10 metres.
