How the FCC defines "bandwidth"

Discussion in 'Amplitude Modulation' started by K4KYV, Oct 6, 2016.

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  1. K4KYV

    K4KYV Premium Subscriber Volunteer Moderator QRZ Page

    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.
  2. W2VW

    W2VW XML Subscriber QRZ Page

    Does Johnny Johnston still write a Q & A column based on regulatory questions somewhere?
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page
  4. W2VW

    W2VW XML Subscriber QRZ Page

  5. K4KYV

    K4KYV Premium Subscriber Volunteer Moderator QRZ Page

    Ah yes, Johnny Johnston. He was the chief-for-life of the amateur radio rulemaking bureau at the FCC, who introduced Docket 20777 back around 1974 that would have outlawed AM had it passed, conducted the Docket-a-Month era at the FCC during the 70s and 80s, and pushed through the bogus AM power limit. He finally retired after holding that position for about 30 years. Even after retiring from the FCC, he wasn't finished with trying to screw over somebody in ham radio; he wrote letters and posted to his column, trying to convince the FCC that using American landline Morse when operating CW is illegal. The FCC folks blew him off on that one.
  6. K5UJ

    K5UJ Ham Member QRZ Page

    Johnny's good for a laugh as long as his opinions stay confined to that website. Here's how he characterizes an OF ham on page :

    Stereotype Z: Over-the-hill 40+ year tenure. Old school. “Grumpy, older guys in their basements with big towers and antennas in their backyards talking to other parts of the world.” Advanced & Amateur Extra Class – mainly in the 66+ demographic. They have caches of old radios and war surplus in their man-caves. Only emerge between DX-peditions and for lunch with other stereotype Zs. Have blown their 401Ks on linear amplifiers and those big towers & antennas. Still irate over incentive licensing and no-code. Fondly remember ham conventions and flea-markets. Hoarding all of the good call signs. Objective: Keep on hamming: “That stereotype Y SOB will have to pry this 1-by-2 from my cold, cold hands.”

    I have yet another T-Shirt idea:
    I Am Stereotype Z

    This in addition to:

    Real Hams Keep Running Out of Clip Leads
    Real Hams Run Separates

    plus a few others.
  7. WA3VJB

    WA3VJB Ham Member QRZ Page

    Johnston has run a 2M net for his chapter of the QCWA in my area.
    I checked in with a cheerful, hey-I-remember-you-as W3BNS, and when it was my turn, I described my part of the hobby, and what a great time it is, and wrapped up by asking John if he's been on AM lately, ahahahaha.
    Well, he was quite stoic and net-controlly, and moved on without comment to the next person on the list.
  8. K4KYV

    K4KYV Premium Subscriber Volunteer Moderator QRZ Page

    Here is the ITU definition of occupied and necessary bandwidth.

    1.152 necessary bandwidth: For a given class of emission, the width of the frequency
    band which is just sufficient to ensure the transmission of information at the rate and with the
    quality required under specified conditions.

    1.153 occupied bandwidth: The width of a frequency band such that, below the lower
    and above the upper frequency limits, the mean powers emitted are each equal to a specified
    percentage β/2 of the total mean power of a given emission.

    Unless otherwise specified in an ITU-R Recommendation for the appropriate
    class of emission, the value of β/2 should be taken as 0.5%.

    Scroll down to page 21:
  9. W2VW

    W2VW XML Subscriber QRZ Page

    Sorry, I just couldn't help myself.

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