The AM Forum

How is the mean power bandwidth of a transmitted signal measured for FCC compliance?

sounds like a new mfj toy will hit the market soon. 

Mean power comes right after the P&M net on slop bucket.

Good question Tom !!

Another:

Do those who object to "excessive bandwidth" feel the same about excessive power ????

 

I thought excessive bandwidth is when the rig goes unstable and excessive power is when the breaker pops.

Excessive power is when during a big pile-up of Americans on a DX station, the guy stops his "59 - chow"  routine and says...  "sorry, USA only PLEASE... uh uh, are you stateside?... oh my god... what is your power and working conditions, old man?"

T

Excessive bandwidth is when you choke on thoes interface units Mr. Vu.

Hi Frank, Buddly, and all,

Well I have been doing some web surfing since posting my question.  This is all new to me.  Perhaps I have answered my own question.

We have been exposed to this occupied bandwidth measurement due to the ARRL petition RM-11306 that wants to emplace this measurement as the basis for sub-band and mode classifications. 

My guess is that this “mean power bandwidth” parameter has popped up since the digital cell phone technology has emerged.  The “mean power bandwidth” may be equivalent to occupied bandwidth, which is the reference I have mostly been reading about. 

I found Agilent (formerly Hewlett-Packard test equipment) references on measuring   
 “occupied bandwidth”.  This may be the popular wireless industry term.  Some of my findings indicate that necessary bandwidth and occupied bandwidth are one in the same by some sources.  And then there is what probably relates to the FCC  –  “authorized bandwidth”.  By my own definitions, necessary bandwidth and occupied bandwidth are different.  They could be the same number however. But in practice, the occupied bandwidth is a result of the implementation of a signal and will be greater than the (minimum) necessary bandwidth. 

A wise-Alex answer to the question of how does one get the occupied bandwidth or mean power bandwidth of a transmitter signal – you push a sequence of buttons on a $12,000 – $25,000+ latest generation wireless test set or spectrum analyzer system.  Voila.  Oh.  But what has really gone on there?

I found out that the general definition of the mean power bandwidth is that 99 % of the total power of the signal’s spectrum is within the 2 bandwidth points.  That is, 0.5 % of the total power is below the lower bandwidth point and 0.5 % is above the upper bandwidth point.  Apparently, some classes of emissions may use a number other than 99 % for the mean power bandwidth determination.  The Agilent E1963A User’s Guide information I looked at stated that the percentage total power number could be adjusted from 70 to 99 %.

So a spectrum analyzer type of device gathers the raw data for the measurement.  A hundred or perhaps thousands of data points (power level vs. frequency increment) must be used to crunch the final number.  I think that you would not need to use data that is any further down on the signal 30 to 40 dB at most.  Adding up all of the data points is called integration and would yield the total power of the signal.  Re-totalizing the power inward from the -40 dB endpoints until 0.5 % of total power is reached yields the bandwidth (frequency) points.  Then the 2 frequency points are subtracted from each other yielding the occupied bandwidth.  This is easy IF you have a spectrum analyzer with built-in computer to do this.

The Agilent application I read about was for looking at the CDMA signals in the cell phone bands.  The expected occupied bandwidths are in the 3 ½ MHz. range. Of course with digital signals, the energy is fairly uniform and constant.

DSB AM voice is the academic question here for us.  I have an old spectrum analyzer.  I can get the basic raw data.  But the eyeballing of a hundred data points or more from a display sweep is doable, but extremely tedious! 

A simpler and more practical method for amateur radio is to just have a spectrum display mask specification like many component specifications or r.f. standards.  This way the old spectrum analyzers can be used easily.  Another method of this would be to just use some level around say the -26 dBc points to declare the occupied bandwidth of the raw data sweep.

I was surprised to find that the mean power term is already in our Part 97 rules.  I don’t know when this crept in.  But it must have permeated the Amateur service due to the technology of the other FCC radio services.

I’m not advocating the inception of mean power or occupied bandwidth for Amateur radio, but just exploring this new term to gain knowledge of it.

so now to be a ham you need a $5 rule book and a $20K spectrum analyzer that should go over well.

Excessive bandwidth is any mode other than CW.

- signed W8JI


I've done 99% power bw measurements on HP and Agilent gear. I'm not familiar with the term mean power bandwidth.

All this illustrates the silliness of 11306. The FCC can barely keep up with keeping commercial RF emitters in to standard (some would argue they don't), let alone do it on the ham bands where one hand in 10,000 might have the appropriate test gear (and brain power) to maintain their compliance.

This is akin to the police making the speed limit 55.000 MPH and car manufacturers still installing the current speedometer (accurate to +/- a few MPH).

Exactly why I don't want any changes, for both reasons.

We are lucky to have what we have and still fight like childern about it.
TheFCC does not need a bunch of whiners crying for more.  fc

It really is next to impossible to do with any accuracy unless you have an analyzer that perfroms the calculation automagically.  You have to integrate under the curve, etc.  I suspect the mean power measurement is one that is video averaged over time then the calculation taken.

Good luck on this if you don't own a HP8591E or a 89660.

73 John