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FCC Releases "symbol rate" NPRM

Discussion in 'Amplitude Modulation' started by K5UJ, Jul 29, 2016.

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  1. W6RZ

    W6RZ Premium Subscriber QRZ Page

    Unfortunately, you're the one that doesn't fully understand baud/symbol rate. OFDM signals (not even mentioned in your W5LEF article) can have very wide bandwidth at a low symbol rate. Here's a OFDM signal with a symbol rate of 278 baud and a bandwidth of 7.77 MHz.

    [​IMG]
     
  2. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    Thanks for your response W6RZ.

    What you stated about the OFDM method is true but I think you are missing the point. Further, how can you possibly know what I do or don't understand regarding digital modulation methods?

    The comments I made were in the Context of the AR service. The statements you made appear to have beeen made in the context of commercial systems.

    Sure, you will find the Orthogonal Frequency Division Multiplex (OFDM) and COFDM modulation methods used in wideband WIFI, WIMAX, 802.11X LAN's, DSL, and in North American digital (HD) radio.

    How many Orthogonal Frequency Division Multiplex (OFDM) or COFDM methods do you find working in the ARS?


    The AR service has available to it more efficient "Open Source" digital modulation methods and protocols than is found in the "closed source" Pactor 4 protocol, a few examples of which I gave in post #15.

    As I also stated to the FCC, regarding Future Directions in the Amateur Radio Service:
    "...do you, the amateur radio operator want to continue with Voice and narrow passband digital systems (such as those listed above in
    D., 1-4), or do you want the ARS to become an extension of the Internet cluttered with digital signals occupying, at minimum the bandwidth of voice modes, and raising the noise floor?"


    Phil
    --------------------------------------------------------------------
    AC0OB - A Place where Thermionic Emitters Rule!
    Besides, when you're a Ham, you experiment with and improve boat anchors - that's what you do!. [​IMG]




     
    Last edited: Sep 2, 2016
    N6YW likes this.
  3. K4KYV

    K4KYV Premium Subscriber Volunteer Moderator QRZ Page

    The new ECFS is supposed to be more user-friendly, but I'm finding it harder to navigate than the old one. It took me several tries to bring up WT Docket 16-239; I kept getting "no results" for my search. Finally I must have jumped through just the right hoops and the comments list appeared.
     
  4. W6RZ

    W6RZ Premium Subscriber QRZ Page

    Pactor 3 is OFDM. It's really the entire point of the NPRM (and discussed in paragraph 6 of FCC 16-96). Today, Pactor 3 is legal because it's OFDM and the symbol rate is 100 baud. But Pactor 4 is illegal because it's a single carrier system at 1800 baud. Yet they occupy essentially the same bandwidth.

    I'm not a big fan of HF e-mail systems, and they seem pretty close to the edge of what's kosher in Part 97. But the cat is out of the bag, and Pactor 3 signals are present on the ham bands. I see absolutely no difference in allowing Pactor 4. Whatever interference is being caused by HF e-mail systems today will be no different with Pactor 4.

    Of course, there's a big knee jerk reaction from the CW and RTTY crowd over "unlimited bandwidth". It's silly. There are exactly zero amateur radio modems available today that have a bandwidth wider than 2.4 kHz. Why would a minor rule change usher in a wave of wide bandwidth modems when a wide bandwidth (greater than 3 kHz) OFDM modem is legal today?

    Because of OFDM, baud rate does not limit bandwidth. Deleting the baud rate language from Part 97 makes perfect sense from a technical point of view. The NPRM is very simple, yet it's been blown way out of proportion by folks that don't understand exactly how baud/symbol rate works.

    BTW, I've read your CV and know that you're an intelligent person with a background in telecommunications. When I saw your post disparaging the ARRL, I was a little surprised and that's what motivated me to respond.
     
  5. K4KYV

    K4KYV Premium Subscriber Volunteer Moderator QRZ Page

    Traditionally the ham bands were divided into two sub-segments, originally phone and CW, with phone being the wide-band mode and CW the narrow. Then along came RTTY, with wider bandwidth but still much narrower than phone, so it was relegated to the "CW" portion. The justification for segregation has always been incompatibility between wide and narrow-bandwidth modes. As newer digital protocols fell into use in amateur radio, some of the digital signals operated with a bandwidth approaching that of SSB, so the question has become, if SSB-wide digital modes are allowed in the so-called "CW" bands, what's the point of even having mode sub-bands at all? Why not just open all the bands to all modes on any frequency, as is the current situation on 160m? That seems to work pretty satisfactorily on Topband, and most other countries in the world, including Canada, have similarly phased out their sub-bands altogether throughout the HF spectrum.

    Here in the US, with the advent of incentive licensing, we now have ended up with our bands diced up into a complex matrix of sub-bands and sub-subbands based on a combination of emission mode and licence class. This is a legacy of the era when the FCC tended to micro-manage the radio services under its administration. The FCC has now moved away from this policy of mico-management, but the legacy remains partly because the country has become so polarised on about every issue imaginable that compromise is difficult, plus it is very difficult to make changes to a deeply-entrenched status-quo.

    My thoughts are to be strongly opposed to the precedent of specific bandwidth limits to any mode. If the 2.8 kHz bandwidth limit to digital signals is adopted, mark my word that it won't be long before we hear clamouring for imposing the same bandwidth standards on SSB, and soon to follow, a 6 kHz bandwidth limit to AM. That's the last thing we need; specific bandwidth limits would impose an undue burden of compliance on the part of licensees, and of enforcement on the part of FCC field personnel. It would stifle innovation; the currently vague bandwidth standard of "good engineering and amateur practice" allows amateur licensees the maximum flexibility for experimentation and self-instruction in the radio art as expressed in Sec 97.1, the basis and purpose of amateur radio.
     
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  6. N6YW

    N6YW Ham Member Volunteer Moderator QRZ Page

    I am contacting ARRL HQ to demand they take notice of these discussions. Perhaps it may help even though I doubt it because I have lost complete faith in their ability to think through anything. Still it's worth a shot.
     
  7. N1EN

    N1EN Premium Subscriber QRZ Page

    One minor point: amateurs do have access to software to generate and decode at least one 2.8kHz wide STANAG mode. One of the reasons we don't see much of it is perhaps because it's a mode that shines at speeds higher than what's currently allowed by Part 97, and it's a bit fussy to set up making narrower/slower modes more attractive.

    I, for one, don't believe that if the proposed rules are enacted, all of a sudden CW and narrow data will disappear under a blanket of ultrawide QRM.

    However, I think that one of the reasons we don't see ultrawide modes today is that in the US at least, there's no incentive to go any wider. It doesn't make sense to go wider if near-maximum-allowed throughput can be achieved with 500-2400Hz wide signals.

    Another reason is, perhaps, limitations of recent technology. It's difficult for us to cleanly transmit wider data signals today; but with the emergence of software-defined radios....maybe some fun new modes become viable.

    Given the slow pace at which US regulations change, it's probably not a bad idea to think about the potential consequences of a proposed rule change. In this case, I'm OK with the idea of leaving some spectrum open to play with such modes, but I don't think it's such a bad idea to protect a portion of the bands from potential/imagined interference of new modes, at least until more is known about how they will coexist with narrower (especially weaker signal) modes.
     
  8. N1EN

    N1EN Premium Subscriber QRZ Page

    I have it on good authority that some senior folks in Newington do lurk here.

    (I don't know about whether they are following this, or any other, particular thread.)
     
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  9. N6YW

    N6YW Ham Member Volunteer Moderator QRZ Page

    Thank you for posting this.
     
  10. AF7TS

    AF7TS Ham Member QRZ Page

    On the technical point above, could you expand on what you mean by 'near maximum allowed throughput '?

    My understanding is that there currently is no limit on how many bits per second could be transmitted, if you have a suitable protocol available; have I missed a separate limitation in the regs?

    73
    Jon
    AF7TS
     

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