Hi Ken Thanks for your feedback. Why should the VSWR be specified with 10 dB attenuation? That would alter (for the better) the specified VSWR itself. I checked th e data sheets of 3 antennas that I'm using (a hybrid bilog, a log-periodic and a horn) and in all of them a "typical" VSWR is specified, without any mention to a 10dB attenuation.
Paolo On Fri, Jul 14, 2023 at 11:33 PM Ken Javor <[email protected]> wrote: > Not expressing an opinion, just listing some facts. > > > > Absent any input attenuation, vswr will be higher than manufacturer > specifies, because the specification is with 10 dB input attenuation > (typically). Therefore, the use of a 6 dB pad, absent any internal > attenuation, will not meet the manufacturer’s spec for vswr, and thus your > uncertainty budget increases. > > > > If your ambient source is brush noise, preselection should help with that, > once you are out of band to it. > > > > Band stop filters will help with known transmitters. > > > > -- > > Ken Javor > > (256) 650-5261 > > > > *From: *Paolo Roncone <[email protected]> > *Reply-To: *Paolo Roncone <[email protected]> > *Date: *Friday, July 14, 2023 at 3:53 PM > *To: *<[email protected]> > *Subject: *[PSES] 6dB pad > > > > Hi all, > > > I'm having a discussion with my colleague about the use of a fixed 6dB > attenuation pad at the input of the EMI receiver for radiated EMI in the > range 30MHz - 6GHz. > The pad I'm using is a Weinschel 6dB N-type 50ohm. > My colleague says the pad is an unnecessary element in the measurement > chain, because the receiver built-in attenuator (typically with 10dB steps) > and proper adjustments in the amplitude settings are enough. > > The reason I'm using the 6dB pad is that - based on my EMI testing > experience, the 6dB pad is a good trade-off between the need to avoid > receiver overload and maintaining a good enough noise floor. > > Without the pad the noise floor is of course lower and everything is fine > as long as the input levels are low enough. > > But in the majority of the test scenarios I'm working on the input levels > are not so low and the 6dB pad is just enough to avoid triggering the auto > built-in 10dB attenuation, that kicks in when the receiver attenuation is > in auto mode, and that is oftentimes an overkill, raising the noise floor > too much, especially in the 1-6 GHz range. > > I have the 6dB pad calibrated for cable loss once a year together with the > N-cable connecting to the antenna. And also the cable calibrated without > the pad. > > > The most typical sources of overload are transient noise generated by > motors (especially brush DC motors) and signals from radio modules like > 2.4G wi-fi, Bluetooth and 5G wi-fi. > > In addition to overload protection, the 6dB pad improves the VSWR at the > cable-receiver interface, as explained in C.J.Paul's EMC Introduction to > EMC (John Wiley 2nd Ed.) Ch.7. > Based on the above I think that, being a resistive network stabilizing the > 50ohm termination impedance at the receiver end, the 6dB 50ohm pad is a > good practice that can prevent overload or excessive auto-attenuation, and > worst-case doesn't do any harm. Or, am I missing something here? > > > I'd like to know if there is someone else in this community who has > experience using fixed attenuation pads at the receiver end of EMI > receivers/spectrum analyzers, or any opinion about it. > > Thanks a lot in advance for any feedback! > > Paolo > ------------------------------ > > 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 All > emc-pstc postings are archived and searchable on the web at: > https://www.mail-archive.com/[email protected]/ > <https://www.mail-archive.com/[email protected]/%20> > > Website: https://ewh.ieee.org/soc/pses/ > Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to > unsubscribe) <https://ewh.ieee.org/soc/pses/list.html> > List rules: https://ewh.ieee.org/soc/pses/listrules.html > > For help, send mail to the list administrators: > Mike Sherman at: [email protected] > Rick Linford at: [email protected] > > For policy questions, send mail to: > Jim Bacher at: [email protected] > ------------------------------ > > To unsubscribe from the EMC-PSTC list, click the following link: > https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1 > ------------------------------ > > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. 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