I couldn't help but jump into this conversation.
Almost any type of signal can be classified as Narrow band or broadband. The only true BB signal would be an impulse. It all comes down to the measurement band-width defined by the standard you are testing to. A repetitive signal such as a square wave rich in harmonic content can be considered both NB and BB depending on the measurement bandwidth. For example: ( a simple example): You have 10kHz square wave fed directly into a spectrum analyzer. Measuring the amplitude with the B.W set at 300kHZ would produce a response you would expect from a typical BB signal. Reducing the measurement bandwidth the peak amplitude would begin to drop until all the individual harmonics could bee seen individually. Then you would have a NB signal. Doing the same with a true impulse would give you constant reduction of amplitude until you hit the noise floor of the spectrum analyzer ( theoretically). The standards define NB and BB signals in reference to the technology the standard is written around. What's BB to one technology could be NB to another! My 2 cents! At 09:41 AM 10/8/99 -0400, Lou Gnecco wrote: > >> -----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). > > * * * * * * * * * * * * * * Paul V. Zahra, NCE NEBS Consulting Engineer ELOB Compliance 408-526-7986 * * * * * * * * * * * * * * "The three happiest days in a boat owners life are the day he buys the boat, the day the boat comes back from the mechanic, and the day he sells the boat and buys a bigger one." --------- 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).
