Grace, The roughly 29.5 dB factor is the voltage divider obtained by driving a 50 Ohm load from a 1500 Ohm source. If the impedance at 30 MHz were really 560 Ohms, the correction factor would be 21.5 dB, not the 29.3 dB shown. So it looks to me as if there is a typo. It would also help to have a schematic of the device. I am away from home right now, and don’t have access to it, but it is described in one of the old FCC or ANSI standards. I recall there being the high value resistance, but also an inductance paralleling the 50 Ohm output to further short out the mains frequency signal. I don’t recall there being a blocking cap, but it seems like there would be one of those as well.
But all that aside, if there is a 1500 Ohm resistance in there, it is hard to figure out how you could get a total impedance line-to-ground of less than 1500 Ohms... Ken Javor Phone: (256) 650-5261 ________________________________ From: Grace Lin <[email protected]> List-Post: [email protected] List-Post: [email protected] List-Post: [email protected] Date: Thu, 4 Dec 2008 14:24:34 -0500 To: <[email protected]> Subject: 3701 Line Probe Dear Members, I purchased and received a 3701 line probe. I need your help to learn this probe. I attach its calibration data below for reference. Two types of calibration data, Impedance and Insertion Loss, come with the probe. Question 1: The impedance varies a lot over the frequency range from 9kHz (1,750.095 ohm) to 30MHz (566.456 ohm). Is this variation acceptable? I plan to use this probe to measure disturbance voltage at load terminals per CISPR 15. The second paragraph under Introduction of the 3701 manual (http://www.ets-lindgren.com/manuals/3701.pdf) states "The Model 3701 Line Probe presents a nominal resistance of 1500 ohms to all voltages on the line. The Line Probe also attenuates noise voltage, so a correction factor must be added to the EMI receiver readings to obtain the proper emission levels on the line." To me, 566.456 ohm is too far away from 1,500 ohm. Question 2: Is the insertion loss the correction factor mentioned in the paragraph quoted above? For example, if the EMI receiver reading is 20 dBuV at 9kHz, should I add 36.078 dB to it as my test data/result? Thank you for your time and look forward to hearing from you. Best regards, Grace Freq (MHz),Impedance (Ohms),Insertion Loss (-dB) 0.009,1764.095,-36.078 0.01,1750.831,-35.505 0.02,1539.087,-32.393 0.03,1526.762,-31.143 0.04,1525.608,-30.51 0.05,1524.686,-30.217 0.06,1523.528,-30.043 0.07,1527.384,-29.935 0.08,1522.35,-29.859 0.09,1523.744,-29.81 0.1,1522.031,-29.77 0.2,1521.142,-29.638 0.3,1520.676,-29.606 0.4,1520.399,-29.592 0.5,1518.446,-29.581 0.6,1517.75,-29.575 0.7,1516.088,-29.569 0.8,1515.104,-29.564 0.9,1513.197,-29.556 1,1511.712,-29.554 2,1486.775,-29.524 3,1450.57,-29.499 4,1405.686,-29.477 5,1356.307,-29.46 6,1304.82,-29.443 7,1247.061,-29.428 8,1175.883,-29.413 9,1118.001,-29.398 10,1069.605,-29.389 15,856.509,-29.35 20,708.009,-29.326 25,633.139,-29.297 30,566.456,-29.284 - 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]>
