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" <vef00...@nifty.com> wrote:
On Fri, 14 Jul 2023 22:53:41 +0200,
Paolo Roncone <paoloc...@gmail.com> 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 <paoloc...@gmail.com> 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
>
> -
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