Hi Ken and Tom Thanks for your inputs. Yes, the 6 dB pad is at the receiver input, in addition or not (depending on the signal level) to the built-in attenuator of the receiver. If the same 6dB pad is put at the antenna output instead of receiver input, it's at the other end of the cable connecting antenna with receiver.
Is it preferable, or recommended, or right to consider the 6dB pad only at the antenna output, rather than at the receiver input? If yes, why, considering that the whole chain (antenna, cable, pad) is nominal 50 ohm? Shouldn't the 6dB pad in any case improve the VSWR or return loss of the antenna-cable-receiver chain? Maybe I'm oversimplifying the picture... Anyway, *assuming* the antenna has a good (> 10dB) return loss or good (< 1.5) VSWR, no need for any pad at all, or better (recommended) no pad at all? Thanks Paolo On Sat, Jul 15, 2023 at 3:30 AM Ken Javor <[email protected]> wrote: > But he is placing the pad at the receiver input in lieu of an internally > selected 10 dB, not at the antenna's output port. > > -- > Ken Javor > > (256) 650-5261 > > On 7/14/23, 6:00 PM, "T.Sato" <[email protected]> wrote: > > On Fri, 14 Jul 2023 22:53:41 +0200, > Paolo Roncone <[email protected]> wrote: > > > 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. > ... > > For example in case of CISPR 16, CISPR 16-1-4 requires antennas to have > return loss higher than 10 dB. > > 6 dB pad at antenna output makes this requirement satisfied regardless > of > return loss of the antenna itself, even for biconical and hybrid > antennas > which will have very bad VSWR. > > Regards, > Tom > > > > On Fri, 14 Jul 2023 22:53:41 +0200, > Paolo Roncone <[email protected]> wrote: > > > 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 <[email protected]> > > > > All emc-pstc postings are archived and searchable on the web at: > > https://www.mail-archive.com/[email protected]/ > > > > Website: https://ewh.ieee.org/soc/pses/ > > Instructions: https://ewh.ieee.org/soc/pses/list.html (including > how to unsubscribe) > > 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: <[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. 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: > https://www.mail-archive.com/[email protected]/ > > Website: https://ewh.ieee.org/soc/pses/ > Instructions: https://ewh.ieee.org/soc/pses/list.html (including how > to unsubscribe) > 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: <[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. 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: > https://www.mail-archive.com/[email protected]/ > > Website: https://ewh.ieee.org/soc/pses/ > Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to > unsubscribe) > 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: <[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. 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: https://www.mail-archive.com/[email protected]/ Website: https://ewh.ieee.org/soc/pses/ Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to unsubscribe) 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: <[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
