> -----Original Message-----
> From: Muriel Bittencourt de Liz
[SMTP:[email protected]] <mailto:[SMTP:[email protected]]>
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:
Arun gave a very good explanation, and here is another one:
Below is an excerpt from one of our books, "PROBLEMS AND SOLUTIONS IN
WIRELESS COMMUNICATIONS AND EMC." I have used this explanation in some of
my courses, and people seem to understand it pretty well. I hope this helps.
*********************** © Copyright 1999 by TEMPEST INC.****************
Chapter 7. Converting Broadband To Narrowband Units And Vice Versa.
This is a source of much confusion to new EMC engineers. Lets look at a
part of the frequency spectrum, say from 20 to 30 MHz :
(1.) When you only have one frequency, say 25 MHz, and its amplitude is
1 volt rms, the spectrum looks like this:
20 MHz.____________________|_________________30 MHz
.........................25 MHz................
(2.) Now lets say you have a waveform composed of 2 signals. One is at 24
MHz and one is at 26 MHz , each one being 1 volt rms. If you look at
either signal alone, its amplitude is still 1 volt rms, but if you look at
them together, the amplitude of the combined wave form will be somewhat
greater.
20 MHz_______|______|_______30 MHz
............24.....26.............
(3.) Now lets say that you have a whole lot of frequencies:
20 MHz.||||||||||||||||||||||||||||||||||||||||||30 MHz
if you take a tiny piece of the spectrum, you may only see one signal _|__
© Copyright 1999 by TEMPEST INC
if you take a piece that is 1 MHz wide, you will see several |||||||
if you take a piece that is 2 MHz wide, you will see even more ||||||||||||||
and the more you see, the more energy you have.
Some signals are broadband. Their spectrum looks like the one in (3.)
above. One example is a square wave. A better example is an impulse. How do
you describe the amplitude of these signals? If you measure them with a 1
MHz bandwidth you will get one answer, if you measure them with a 10 MHz
bandwidth you will get a different answer. This is why we have broadband units.
With broadband units we can say that this signal gives you x volts for
every megahertz-sized piece of the spectrum that you use to measure it.
For example, if the signal in (3) gives you 10 volts when you take a 1
MHz
piece, it will give you 20 volts if you take a 2 MHz piece, and 30 volts if
you take a 3 MHz piece.
The bigger the bandwidth, the more volts you get.
In this case, we would say that the signal gives you 10 volts per
Megahertz.
Now lets say that you look at this signal with a 10 MHz bandwidth:
© Copyright 1999 by TEMPEST INC
We would see 10 Volts/MHz x 10 MHz bandwidth = 100 Volts
if we look at it with a 2 MHz bandwidth, we would see
10 volts/MHz x 2 MHz = 20 Volts
what if we only looked at it with a 500 kHz bandwidth?
500 kHz = 1/2 MHz
10 V/ MHz x 1/2 MHz = 10 x 1/2 = 5 Volts
now lets do some problems:
******************© Copyright 1999 by TEMPEST INC.****************************
For more info, see:
http://www.tempest-inc.com/pubs1.htm
Regards,
Lou
.............................................................................
LOUIS T. GNECCO M.S.E.E., PRESIDENT
TEMPEST INC. 112 ELDEN ST. HERNDON, VA 20170
(703) "TEMPEST" (836-7378)
CERTIFIED ELECTROMAGNETIC COMPATIBILITY ENGINEER: CERT.# EMC-000543-NE
CERTIFIED ELECTROSTATIC DISCHARGE CONTROL ENGINEER: CERT. # ESD-00143-NE
CERTIFIED TEMPEST PROFESSIONAL, LEVEL II
..............................................................................
---------
This message is coming from the emc-pstc discussion list.
To cancel your subscription, send mail to [email protected]
with the single line: "unsubscribe emc-pstc" (without the
quotes). For help, send mail to [email protected],
[email protected], [email protected], or
[email protected] (the list administrators).
