Ed and I are on the same page about 95% of the time, and that is a conservative estimate. But this time he is wrong. Not in the fundamental concepts, but as they apply to the control of RE and RI.
Certainly every electronic device can be both an emitter (culprit) and receiver (victim). That concept is valid. And if uncontrolled unintentional emitters could emit at levels that cause susceptibility in other victims, then Ed’s post would be exactly correct. Bu that does not, and cannot happen. The question comes down to numbers: at what levels do unintentional emitters emit, and at what level are unintentional victims susceptible? Unintentional is key here, as we shall see shortly. The intentional receiver of rf energy is a radio receiver. A good quality radio has a 20 dB noise figure. Of course you can do better than that, but 20 dB is very good. If you specify sensitivity with a 10 dB s/n ratio, you are looking at a signal of –104 to –94 dBm into 50 Ohms, assuming a receiver bandwidth between 10 – 100 kHz. As an rf potential, you are looking at 3 – 13 dBuV. Or perhaps more instructively, 0.04 - 0.125 pW. The A/D, or servo system device, or intercom, or medical device, you name it, is looking for millivolts or at least 100s of microvolts, and it is looking for those values typically in a spectrum well below the broadcast bands, and certainly below the range over which radiated emissions are controlled. So to say that we control radiated emissions to protect non-antenna-connected victims operating at signal levels orders of magnitude higher than the radios which are the reason for RE control, and which operate below the BCB spectrum, is too much of a stretch. On the flip side, the argument that we control radiated emissions to protect anything besides radio BCB reception also falls flat when you look at how much unintentionally radiates. If the signal integrity work on a piece of electronics has been done properly (i.e., the thing works), the common mode noise which is the source of radiation from the equipment and its connected cables is well under one Volt in the time domain, and some minute fraction of a Volt in any frequency domain bucket or bandwidth. If you apply a huge signal level, say 10 mV, to the terminals of a biconical antenna, a device that was designed to radiate, then the field you get at one meter is somewhere between 2 and 7 mV/m, depending on specific frequency. Nothing besides an antenna-connected radio can respond to that. If you don’t have a feel for the numbers, apply the conversion factors of MIL-STD-461 CS114 and/or IEC 61000-4-6 to get a feel for the resultant applied stress on the test sample-connected cable. For CS114, you are looking at 1.5 mA per V/m in the broadcast bands. So that corresponds to inducing 3 – 11 uA injected on test sample-connected cables. For 61000-4-6 you are looking at 1 Volt per Volt/meter. So you would inject (from a 150 Ohm source impedance) an open circuit value of 2 – 7 mV. Again, injecting these out-of-band common mode signals into non-antenna-connected-electronics is a waste of time. The clear and undeniable truth is that radiated emission limits are necessary to protect BCB radio reception, and only that. Ken Javor Phone: (256) 650-5261 ________________________________ From: "Price, Edward" <[email protected]> List-Post: [email protected] List-Post: [email protected] List-Post: [email protected] Date: Mon, 1 Dec 2008 06:18:32 -0800 To: <[email protected]> Conversation: EMI Receivers - Now Terminology Subject: RE: EMI Receivers - Now Terminology ________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of Ken Javor Sent: Friday, November 28, 2008 8:08 AM To: Untitled Subject: Re: EMI Receivers With this sloppy terminology, rife in the commercial world, we are raising a generation of EMC engineers who have no clue why they do what they do, other than they have to meet some legal requirement before marketing a product. It is bad enough that I have seen in this forum otherwise well-regarded engineers claiming that radiated emission requirements are there to protect all electronics from interference, as opposed to radio receivers, which are the sole victim protected by radiated emission limits. Non-antenna-connected electronics don’t require that level of protection. Happy Holidays! Ken Javor While Ken raises valid points, I think he is still defining interference too restrictively. While many official limitations on radiated emissions have been set to provide protection for receiving systems, this has only been the historical precedent. There is no reason why a radiated emission limit cannot also be used to protect non-receivers. Actually, "non-receivers" is a bad term, because everything is a receiver. I have seen many examples of "non-receivers" (things like A to D converters or servo systems) which, either by poor design or construction, make fairly good receivers. It can certainly be argued that undesired responses to external energy should be controlled by immunity requirements. Most of the time, that's true. But COMPATIBILITY is a balance between control of emissions and ensurance of immunity. You may go to extremes in both directions, or you can seek a balance (typically defined by cost, weight, size, politics). And that's why radiated emission limits can protect things other than intentional receivers. Ed Price [email protected] <blocked::mailto:[email protected]> WB6WSN NARTE Certified EMC Engineer & Technician Electromagnetic Compatibility Lab Cubic Defense Applications San Diego, CA USA 858-505-2780 (Voice) 858-505-1583 (FAX) Military & Avionics EMC Is Our Specialty - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]>
