The digital data links that I regularly see have both an "avalanche" and a "jitter" effect. By those totally subjective terms, I mean that once you get to a point where the bit error rate (BER) goes from near zero to one percent or so, you need very little more decrease in desired signal level to jump up to 100%. Many times, the difference between near zero BER and totally dead is only 2 dB. And, if you set the level to the midpoint, you will get values that cycle across a wide range of BER. Noisy data usually needs you to mentally integrate the results and simply declare "Yep, that's the spot right there!". <grin>
Regardies, 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: Tuesday, May 08, 2001 4:40 AM >To: 'Ken Javor'; EMC-PSTC (E-mail) >Subject: RE: RF testing question > > > >Hi Ken, > >Let me try to explain it better. The standard asks that you >stop reducing >the signal strength one you cross the 25% threshold. I would >imagine that it >would be very hard to get exactly 25% So for example if you got a 10 % >failure rate at one level then reduced the transmit signal >strength by 1 dB >and got a 30% failure rate you would stop there. Also many >digital systems >would likely have an all or nothing response so getting a 25% >failure rate >would be not possible. >As to "restoring to full power" the power level of the >transmitter in this >case is fixed, the signal strength of the system is reduced by adding >attenuation in line to the transmitter antenna. This is simply >removed once >the threshold is determined and the interference signal is added to the >equation. > >Regards > >Kevin > > > -----Original Message----- > From: Ken Javor [mailto:[email protected]] > Sent: Monday, May 07, 2001 10:48 PM > To: Price, Ed; 'Kevin Harris'; EMC-PSTC (E-mail) > Subject: Re: RF testing question > > 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)? > ------------------------------------------- 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,"
