Either I am being dense, or there is not enough info in the problem statement. Mr. Harris states that after determination of the interference level (that signal which yields no better than 25% error rate plus 40 dB) the transmitter is returned to full power. How is full power defined? The success or failure of this test will depend on that. Also, the words 25% OR MORE of the signals are not understood (my emphasis) are unclear. If I wanted to pass this test, I would reduce the transmitter level until no signals are understood, then add 40 dB to that number and I would get a lower susceptibility signal than if I had stopped at precisely the 25% level. So to me it seems that there are two uncontrolled variables here: the baseline for establishing the susceptibility signal level, and the level at which the desired signal is transmitted. What am I missing (besides maybe some of my dear, departed brain cells)?
---------- >From: "Price, Ed" <[email protected]> >To: "'Kevin Harris'" <[email protected]>, "EMC-PSTC (E-mail)" <[email protected]> >Subject: RE: RF testing question >Date: Mon, May 7, 2001, 1:47 PM > > > Kevin: > > You are actually testing a signal-to-noise ratio. The desired signal is > reduced until you get to a certain level of degradation (which is unique to > the receiver you have chosen). You then use that level to determine the > amount of undesired (interfering) signal. You apply that undesired signal, > while also applying the restored desired signal. And if the message failure > rate is under 25%, you pass. > > This method actually adjusts the interfering signal level to match the > sensitivity of the selected receiver. If your receiver is more sensitive to > your desired signal, then you are right, the applied undesired signal level > will also be lower. > > You should use the same illuminating antenna for both signals. Be sure your > power combiner and antenna balun are safe from RF overload. If you can, use > isolators to protect the two signal sources. If isolators are not available, > try using about 6 dB attenuators ahead of the signal sources. > > Unless the antenna is uniquely designed into the receiver, military testing > prefers that you do this all within coax, in essence performing an antenna > port conducted susceptibility test. > > Regards, > > Ed > > Ed Price > [email protected] > Electromagnetic Compatibility Lab > Cubic Defense Systems > San Diego, CA USA > 858-505-2780 (Voice) > 858-505-1583 (Fax) > Military & Avionics EMC Services Is Our Specialty > Shake-Bake-Shock - Metrology - Reliability Analysis > > >>-----Original Message----- >>From: Kevin Harris [mailto:[email protected]] >>Sent: Monday, May 07, 2001 9:19 AM >>To: EMC-PSTC (E-mail) >>Subject: RF testing question >> >> >> >>Hello, >> >>I'm puzzled by a proposed RF link performance standard I have >>just reviewed >>that is calling for some immunity to inband interference signals. The >>proposed procedure to do this to is to place a system receiver in an >>anechoic room and then transmit to it. The transmitter signal >>strength is >>then gradually reduced until 25% or more of the signals are >>not understood >>by the receiver. This level is recorded and then an inband interference >>signal at 40dB greater than the receiver level recorded earlier is >>introduced to the system. The original transmitter is restored >>to full power >>and the system must receive any transmission from it without fault. My >>question is why would you base an interference signal based on receiver >>sensitivity. This would mean if you had a receiver that was >>more sensitive >>than the other guy you would be subject to a less intense interference >>signal. Why wouldn't the interference level be fixed? Not >>being an RF guru, >>this seems plain wrong to me but perhaps there is a good >>technical reason >>for it. Any thoughts? >> >> >>Regards, >> >>Kevin Harris >>DSC >> >> > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: [email protected] > Dave Heald [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > http://www.rcic.com/ click on "Virtual Conference Hall," > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall,"
