[AMRadio] FCC's Definition of Bandwidth


Robert Bethman oldrotorheadsarge at outlook.com
Thu Oct 6 18:41:39 EDT 2016


Don and the group,

Welcome to the Land of Oz!

I've spent a total of 34+ years dealing with U.S. Government "Rules and Regulations".

You've hit upon the crux of all of its entirety!  Things have been put into words at very different times by far too many disparate entities!

None of which have been reconciled nor thoughtfully been adequately proofread by the mess in Washington!

Those entities that I worked for have never found ANY cohesive pieces amongst anything that has CFR in its title!

I'd also add that submitting any query to the "responsible" entity for such, only results in an answer that is as obscure to the portion queried, or adds more ambiguity than one began with.

Best of luck attempting to find an answer!

Bob - N0DGN

-----Original Message-----
From: AMRadio [mailto:amradio-bounces at mailman.qth.net] On Behalf Of Donald Chester
Sent: Thursday, October 06, 2016 4:47 PM
To: amradio at mailman.qth.net
Subject: [AMRadio] FCC's Definition of Bandwidth

FCC Part 2 (General Rules and Regulations) thus defines occupied bandwidth:

§ 2.202 Bandwidths.

(a) Occupied bandwidth. The frequency bandwidth such that, below its lower and above its upper frequency limits, the mean powers radiated are EACH equal to 0.5 percent of the total mean power radiated by a given emission. 

Part 97 defines bandwidth differently:

§97.3 Definitions.

(a) The definitions of terms used in Part 97 are:

(8) Bandwidth. The width of a frequency band outside of which the mean power of the transmitted signal is attenuated at least 26 dB below the mean power of the transmitted signal within the band.

I see a 6 dB discrepancy between the Part 2 and Part 97 definitions. 0.5 percent is a ratio of 1/200, or minus 23 dB. According to the Part 2 definition, it appears that the power radiated above the defined frequency band is 0.5 percent, and the power radiated below the defined frequency band is another 0.5 percent; adding the two together makes the total power radiated outside the defined band 1 percent, which would equal minus 20 dB.

According to the Part 97 definition above, the total mean power radiated above and below the defined frequency band is minus 26 dB. This means that, according to the amateur rules, the definition of occupied bandwidth is more severe by 6 dB, than the definition under the general rules and regulations.

Am I missing something, or are amateur signals under a stricter standard than the general definition? §2.202 (a) goes on to state: "In some cases, for example multichannel frequency-division systems, the percentage of 0.5 percent may lead to certain difficulties in the practical application of the definitions of occupied and necessary bandwidth; **in such cases a different percentage may prove useful**". So perhaps the FCC has intentionally applied a stricter bandwidth standard for amateur radio than for other services? Or is this an error where someone added 6 dB instead of subtracting it. Or maybe I'm the one reading it wrong.

I'd be interested in other opinions. 


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