Why (and How) You Should Urge the FCC to Reject the ARRL’s Symbol Rate Petition

Discussion in 'Working Different Modes' started by AA6YQ, Dec 7, 2013.

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  1. AA6YQ

    AA6YQ XML Subscriber QRZ Page

    The ARRL briefing memo is incorrect. Their petition's proposed elimination of the 300 baud symbol rate limit applies to the sub-bands defined in 97.221 (b). If adopted, it will enable automatic stations to use digital modes up to 2800 hertz in width within these sub-bands. Today, the widest digital mode used by automatic stations in these sub-bands is Pactor 3, at 2200 hertz. Even though there's no regulatory limit on wider modes, the 300 baud symbol rate limit in combination with the passbands of most HF transceivers prevents any benefit from bandwidths wider than 2200 hertz.

    [FONT=&amp]When the FCC added Section 97.221 in April 1995, it stated in PR Docket No. 94-59 “We do recognize the concerns of those who oppose the proposal on the basis of potential interference, and in response to these concerns we are limiting when automatic control can be employed. First, the control operator of the station that is connected to the automatically controlled station must prevent the automatically controlled station from causing interference. Second, we are designating sub-bands to which transmissions between two automatically controlled stations are confined. These sub-bands are a small portion of the spectrum otherwise available for digital emission types. We also are confident in the ability of the amateur service community to respond, as it has in the past, to the challenge of minimizing interference with novel technical and operational approaches to the use of shared frequency bands.”

    The 97-221 (b) sub-bands are explicitly shared with other digital emission types. The FCC did not, for example, dedicate 20% of the 30m band (10,140 to 10,150) for the exclusive use of automatic stations.

    Automatic busy frequency detectors are just the sort of "novel technical and operational approaches" that the FCC expects the amateur radio community to develop and employ to minimize interference. Banning CW or conversational modes in these sub-bands is explicitly not acceptable.

    [/FONT]
     
  2. AA6YQ

    AA6YQ XML Subscriber QRZ Page

    That's false. If adopted, the ARRL petition will allow automatic stations to use wider modes than they can use today. No one has refuted this point.
     
  3. KV6O

    KV6O Ham Member QRZ Page

    Today, there is no bandwidth limit, only a symbol rate limit. The petition actually sets a limit, 2.8k.

    Steve
    KV6O
     
  4. AA6YQ

    AA6YQ XML Subscriber QRZ Page

    My response was quite specific: What is relevant are the sub-bands defined by 97.221 (b) in which automatic operation at bandwidths greater than 500 hertz is permitted.

    I've made no claim that busy frequency detectors will eliminate all interference from automatic stations. Usage reports from the WinMOR and ALE communities show current busy frequency detectors to be about 80% effective. Thus deploying them reduces the incidence of interference by a factor of 5.

    A 2700 hertz wide mode with more sub-carriers and more sophisticated encodings than Pactor 3 would likely not be supported by your rig. Why not? Key electrical characteristics like group delay are not sufficiently uniform across the entire passband.

    With the 300 baud symbol rate limit in place, more sub-carriers (OFDM) and more sophisticated encodings are the only way to increase transfer rate - but Pactor 3 (at 2200 hertz) is the widest multiple sub-carrier (OFDM) mode that most HF transceivers can support. That's why you don't see modes wider than 2200 hertz being used by automatic stations in the 97-221 (b) sub-bands. Even though there is no regulatory limit on bandwidth; the 300 baud symbol rate limit makes bandwidths wider than 2200 hertz ineffective.

    Remove the 300 baud symbol rate limit, as the ARRL petition would do, and we can now develop faster modes by means other than employing large numbers of sub-carriers; this will enable the development of 2800 hertz modes that are faster than Pactor 3 and still work with most HF transceivers. That's the objective of the ARRL petition. I don't disagree with this objective; I only disagree with its implementation without a concurrent effort to prevent any increase in interference from automatic stations.
     
    Last edited: Dec 21, 2013
  5. AA6YQ

    AA6YQ XML Subscriber QRZ Page

    Even though there is currently no regulatory limit on bandwidth; the current 300 baud symbol rate limit makes bandwidths wider than 2200 hertz ineffective for automatic stations, which must work with most HF transceivers and their passband limitations. For this reason, there are no automatic stations now using modes wider than 2200 hertz in the 97.221 (b) sub-bands. By removing the 300 baud symbol rate limit, the ARRL petition will make it possible for such stations to use 2800 hertz modes. Automatic stations without busy frequency detectors will be able to employ modes significantly wider than what they use today, thereby generating more interference than they do today.
     
  6. W4PG

    W4PG Super Moderator Lifetime Member 279 Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    Bob <------- shaking his head.

    Dave, it's difficult to accept that the ARRL petition will allow wider modes than can be used today when the current FCC rules DO NOT limit the bandwidth of those modes. I'm beginning to wonder if you have a clue what the rules say. Now until today, I *thought* that digital modes in the cw/digital sub-bands were limited in bandwidth. I realized that was not the case. No amount of screaming and yelling on your part will change that.

    You simply need to take a close look at what is relevant.
     
  7. AA6YQ

    AA6YQ XML Subscriber QRZ Page

    You continue to ignore the point: even though there is no currently regulatory limit on bandwidth, for automatic stations, the 300 baud regulatory limit on symbol rate makes modes wider than 2200 hertz un-usable because they wouldn't work with most HF transceivers. The proof of this assertion: there are no modes wider than 2200 hertz in use today by automatic stations on HF bands. The widest mode in use is Pactor 3, whose bandwidth is 2200 hertz.

    By eliminating the 300 baud regulatory symbol rate limit, the ARRL petition would allow the development of 2800 hertz wide modes that will work with most HF transceivers. Automatic stations without busy frequency detectors that adopt these modes will generate more interference than they do today.
     
  8. K2NCC

    K2NCC Ham Member QRZ Page

    You say that, several times even, but it's an assumption at best. Do you REALLY suffer from chronic interference from digital modes? Probably not. Will you if they lift the 2200 limit? Probably not. Do you even use digital modes? Probably not.
     
  9. AA6YQ

    AA6YQ XML Subscriber QRZ Page

    The widest digital mode commonly used by automatic stations operating in the 97.221 sub-bands is Pactor 3, at 2200 hertz; that's a fact.

    If adopted, the ARRL petition will enable the development of significantly faster digital modes with widths up to 2800 hertz; that's the expressed objective of the ARRL petition.

    Operators and users of automatic stations are advocating for the adoption of the ARRL's proposal because they want their email messages delivered more rapidly, as they state in comments filed with the FCC; it's no stretch to assume that such operators and users will deploy faster, wider modes if they become available.

    Automatic stations without busy frequency detectors that are upgraded from a 2200 hertz mode to a 2800 hertz mode will without question generate more interference to ongoing QSOs than they do today; you need nothing more sophisticated than arithmetic to confirm this.

    Yes. While in QSO, I have been QRM'd by automatic stations on the 30m and 40m bands. I have a PTC-IIe modem capable of decoding Pactor and Pactor 3, and thus could accurately determine the source of the interference; it's the small light grey unit on top of the Yaesu Mark-V on the left side of this picture.

    Yes -- and more frequently than in the past.

    Since April 1993, I've made 2357 RTTY QSOs, 1025 PSK QSOs, and a handful of QSOs in modes like Olivia and JT65. I've attained the ARRL's RTTY Honor Roll with credit for 336 DXCC entities.

    I am the author of the free-ware DXLab Suite, whose WinWarbler component supports digital mode operation in RTTY, PSK31, PSK63, and PSK125; DXLab received the ARRL's Technical Innovation Award in 2008. I added PSK125 support to AE4JY's PSKCORE engine (used in WinWarbler and by other digital mode applications), and improved MMTTY's RTTY demodulator.

    Any other bad guesses?
     
  10. K2NCC

    K2NCC Ham Member QRZ Page

    None. Thank you for enumerating your accomplishments for me.
     
    Last edited: Dec 24, 2013
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