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 ed.pr...@cubic.com 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:harr...@dscltd.com] >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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall,"
