Hi Ed, If this were a true signal to noise test wouldn't the interfering signal be referenced to the power of the desired signal and not the sensitivity of the receiver? I rechecked what the standard called this particular test and they call it "Interference within the band". Interference is a phenomenon which is peculiar to whatever location you happen to place your device. It will not change in level when you change to a different receiver with a different sensitivity so shouldn't a proper test designed for testing inband immunity select a fixed level of interference. Did I miss something in your explanation?
Best Regards, Kevin Harris Manager, Approval Services Digital Security Controls 3301 Langstaff Road Concord, Ontario CANADA L4K 4L2 Tel: +1 905 760 3000 Ext. 2378 Fax +1 905 760 3020 Email: [email protected] <mailto:[email protected]> -----Original Message----- From: Price, Ed [mailto:[email protected]] Sent: Monday, May 07, 2001 2:47 PM To: 'Kevin Harris'; EMC-PSTC (E-mail) Subject: RE: RF testing question 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 ------------------------------------------- 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,"
