Hello,
I quote MIL STD 462 # 4.2.6:
A: The EMI meter shall be tuned over a range of * 2 impulse
band widths around the centre frequency of emission. A change in peak
detector response of 3 dB or less indicates a broad band emission. A change
of greater than 3dB indicates a narrow band emission.
B: Measure the PRF of the emission. If the PRF is less than
or equal to the impulse BW of EMI receiver it is a broad band emission, if
greater it is a narrow band emission.
Also practically, the easiest way to determine a NB emission
is to drop down or increase the measuring BW 1 or 2 steps in a routine EMI
receiver sweep around the emission in a broad span; if the emission remains
constant, it is NB emission. Broad band emissions would drop approx 10 dB
per step change in the bandwidth.
Sweep time could also be varied, time domain BB emissions
would change with sweep time; frequency domain NB emissions would more or
less remain constant.
You have to normalise BB emissions to a 1MHz BW,
irrespective of actual measurement BW used. Otherwise, people could shonk a
broad band CE03 or RE02 test pass.
Computer clocks (and its harmonics) and intentional CW or
modulated transmitters generally generate frequency domain NB emission.
Commutator motors, thermostats, serial comms links generally generate time
domain BB emissions.
And finally yes, MIL STD 461D and most commercial standards
have got around this NB/BB emission discrimination mess by specifying the
measurement BW.
Hope this helps.
Regards
Arun Kaore
EMC Engineer
ADI Limited
Test & Evaluation Centre
Forrester Road, St Marys NSW 2760
P O Box: 315, St Marys NSW 1790
Tel: 61 2 9673 8375
Fax: 61 2 9673 8321
Email: kao...@sg.adi-limited.com.au
<mailto:kao...@sg.adi-limited.com.au>
-----Original Message-----
From: Price, Ed
[mailto:ed.pr...@cubic.com] <mailto:[mailto:ed.pr...@cubic.com]>
Sent: Friday, 08 October, 1999 4:21
To: 'Muriel Bittencourt de Liz'; Lista
de EMC da IEEE
Subject: RE: broadband & narrowband
emissions
> -----Original Message-----
> From: Muriel Bittencourt de Liz
[SMTP:mur...@grucad.ufsc.br] <mailto:[SMTP:mur...@grucad.ufsc.br]>
> Sent: Thursday, October 07, 1999 5:43 AM
> To: Lista de EMC da IEEE
> Subject: broadband & narrowband
emissions
>
>
> Group,
>
> I'd like to have a clear definition of
what are narrowband and broadband
> emissions. This question may seem very
plain for many members of
> EMC-PSTC, but I always heard/saw this
definition for emission and I
> still couldn't make them clear to me..
>
> Thanks in advance for your attention
>
> Regards
>
> Muriel
>
> --
>
======================================================================
> Muriel Bittencourt de Liz
> GRUCAD - Group for Conception & Analysis
of Electromagnetic Devices
> Santa Catarina Federal University - UFSC
> PO Box: 476 ZIP: 88040-900 -
Florianópolis - SC - BRAZIL
> Phone: +55.48.331.9649 - Fax:
+55.48.234.3790
> e-mail: mur...@grucad.ufsc.br
<mailto:mur...@grucad.ufsc.br>
> ICQ#: 9089332
> Alternativa Adreso: mur...@esperanto.nu
<mailto:mur...@esperanto.nu>
>
> ---------
Muriel:
Narrowband and Broadband are the two
extremes of the spectral distribution of a signal's power.
The classic NB emission has all of its power
contained within a narrow range of the spectrum. Think of a perfect sine
wave generator, with no sidebands or frequency instability. But how narrow
is narrow? All of the power is within 100 Hz? Or 10 Hz? Or 1 Hz? Or......
Classifying a signal as NB depends a lot on
your prejudices and experiences. At 10 GHz, a radar signal might occupy 10
MHz of spectrum. That's a lot of spectrum to an audio guy, even though it's
only 0.1% wide!
My particular experience says that a signal
is NB if its occupied bandwidth is around 1% or less.
The classic BB emission has its power
distributed over a wide range of the spectrum. Think of the spectra from an
infinitely fast transition. The power will exist no matter where you choose
to sample it.
Practically, there are no perfect NB or BB
emissions. The problem lies in where (and how) we try to define the dividing
line. Should we use percentage of occupied bandwidth? Or tuneability (with
what detector bandwidth)? Or maybe modulation repetition rate? Is a NB
signal which hops around quickly still NB? What about two NB signals real
close together?
Have you ever heard the story about the 4
blind men and an elephant?
Regards,
Ed
:-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-)
Ed Price
ed.pr...@cubic.com
<mailto:ed.pr...@cubic.com>
Electromagnetic Compatibility Lab
Cubic Defense Systems
San Diego, CA. USA
619-505-2780 (Voice)
619-505-1502 (Fax)
Military & Avionics EMC Services Is Our
Specialty
Shake-Bake-Shock - Metrology - Reliability
Analysis
:-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-)
---------
This message is coming from the emc-pstc
discussion list. To cancel your subscription, send mail to
majord...@ieee.org <mailto:majord...@ieee.org> with the single line:
"unsubscribe emc-pstc" (without the quotes). For help, send mail to
ed.pr...@cubic.com <mailto:ed.pr...@cubic.com> , jim_bac...@monarch.com
<mailto:jim_bac...@monarch.com> , ri...@sdd.hp.com <mailto:ri...@sdd.hp.com>
, or roger.volgst...@compaq.com <mailto:roger.volgst...@compaq.com> (the
list administrators).
---------
This message is coming from the emc-pstc discussion list.
To cancel your subscription, send mail to majord...@ieee.org
with the single line: "unsubscribe emc-pstc" (without the
quotes). For help, send mail to ed.pr...@cubic.com,
jim_bac...@monarch.com, ri...@sdd.hp.com, or
roger.volgst...@compaq.com (the list administrators).
