We have been conditioned to accept the magic of automated controls and the digital mindset. Commanding a signal source to step through a series of frequencies, we expect that the resultant RF field will be as clean and predictable as our logic. It's easy to overlook that when a synthesized signal generator is changing from State A to State B, a lot of things go wild and crazy for a short period of time. Since whatever gets out of the signal source gets amplified and applied to the EUT, we really need to fully understand what the signal source REALLY produces.
That legendary good test lab will have spent some time with their field generation system, examining the transients and uncertainties created when their generator steps frequency, modulation and levels. They will have looked at all critical frequencies (a synthesizer may have several fixed oscillators, a stepped / swept oscillator, amplification paths and bandpass filters which are switched in various combinations throughout a wide frequency sweep). They will know what happens with amplifier overshoot with pulse modulation. Just as importantly, they will know what their amplifier does when presented with the generator's output. Amplifiers cartainly have distortion and compression effects, but they also present an opportunity for more strange effects. They need to be aware of the possibilities of parasitic oscillations and amplifier responses to stepped changes. Only when you really know what your immunity system is creating can you develop test strategies that eliminate these variables. Ed Price WB6WSN Chula Vista, CA USA -----Original Message----- From: John Woodgate [mailto:[email protected]] Sent: Thursday, April 10, 2014 8:30 AM To: [email protected] Subject: Re: [PSES] Radiated Immunity Test Methods In message < <mailto:64D32EE8B9CBDD44963ACB076A5F6ABB0268DF76@Mailbox-Tech.lecotech.local > 64D32EE8B9CBDD44963ACB076A5F6ABB0268DF76@Mailbox-Tech.lecotech.local>, dated Thu, 10 Apr 2014, "Kunde, Brian" < <mailto:[email protected]> [email protected]> writes: >From previous discussions on this email group some experts believe that >phenomena occurs because the Signal Generator glitches during a >frequency or power level change causing the failure which would be a >false failure but inherent to most such test equipment. It can't help but 'glitch', because a step change in frequency or level generates a transient spectrum containing many frequencies. This applies even if the change occurred at a zero crossing, and unless it was done quite slowly (when the transient spectrum would be dense but weak). - ---------------------------------------------------------------- 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.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) 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]>
