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Any advantage keeping a 500Hz bandwidth automatic digital system within the ACDS HF segments?

Discussion in 'Ham Radio Discussions' started by KX4O, May 3, 2018.

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  1. KX4O

    KX4O Ham Member QRZ Page

    Given the 97.221 rules, is there any advantage of an automated digital system requiring 500 Hz or less spectrum bandwidth to stay within the Automatically Controlled Digital Station (ACDS) band segments?
  2. K0RGR

    K0RGR Premium Subscriber QRZ Page

    This is the only real bandwidth limitation for digital modes spelled out in the rules. Hence, they could be using something much wider, which does happen frequently under manual control. Many digital modes are 1 kHz wide, and even 2 kHz wide. The 2 kHz modes aren't often heard on HF, but the 1 kHz variety are indeed. Anything wider than a CW signal gives the telegraphers in our ranks the cold sweats, for fear their preferred frequency segment will be buried in wide digital signals.
  3. KK5JY

    KK5JY Ham Member QRZ Page

    I believe 47 CFR 97.3(c)(2) requires all data modes to be <= 500Hz wide below 30MHz. I don't doubt that people break this rule, but in order to be used in the "data" segments lawfully, they do have to be 500Hz or less in total bandwidth (which is also defined in the rules). Wider modes (such as the DV modes) aren't considered "data," and have to be done outside those segments.

    Above 30MHz, the bandwidth restriction doesn't exist -- those bands have lots of free MHz, so a width restriction was probably not considered necessary (but that's just my conjecture).

    Oops, that's not quite true... sorry about that. The bandwidth restriction appears to only apply to certain emission designators.
    Yes, if you are operating an automatic digital station, regardless of bandwidth, it must stay within those segments for operation to be lawful. The only exception to this is explained in 47 CFR 97.221(c)(1).
  4. KX4O

    KX4O Ham Member QRZ Page

    (c) Except for channels specified in § 97.303(h), a station may be automatically controlled while transmitting a RTTY or data emission on any other frequency authorized for such emission types provided that:
    (1) The station is responding to interrogation by a station under local or remote control; and
    (2) No transmission from the automatically controlled station occupies a bandwidth of more than 500 Hz.

    This is precisely the way this particular digital system will be accessed... by a human operator under local or remote control with his/her TNC/Rig and all within a bandwidth of 500Hz or less.

    Given these attributes, can I assume it is legal to tune this 97.221(c) compliant system "on any frequency authorized for such emission types" even if outside the ACDS?
  5. KK5JY

    KK5JY Ham Member QRZ Page

    Yes, that is my understanding.

    So the question becomes picking a smart place to place such a system. If you place it right in the middle of a FT8 watering hole, you're going to attract some unwanted fan mail. :)
    Last edited: May 3, 2018
  6. KX4O

    KX4O Ham Member QRZ Page

    Thank you.

    Swinging back to my original question... I wonder if there are any advantages to be found in moving outside the ACDS. If I stay inside the ACDS, I have to compete with other automated systems (P3/Winlink?) with potential modulation much wider than 500 Hz. I realize I have to tolerate "manned" transmissions larger than 500 Hz up to SSBwidth anywhere.

    I probably won't move outside the ACDS in the hope of maintaining harmony with the most users, but certainly want to explore the topic a bit. I never intend to have a spectral footprint wider than 500 Hz. Hopefully that is a good compromise to all.
  7. KK5JY

    KK5JY Ham Member QRZ Page

    I think you and I have both covered this. It's about sharing the bands with others in a way that is agreeable to everybody.
  8. KY5U

    KY5U Subscriber QRZ Page

    Interesting discussion. What would you use this automatic data station for? I keep waiting for a fully automatic digital mode, a "QSO-O-Matic" as it were, where you leave your rig running in auto mode and come back later to collect the logs.
  9. KK5JY

    KK5JY Ham Member QRZ Page

    There are some hams outside the US who are already doing this with FT8. It's not quite street legal in the US, but apparently that's not a problem elsewhere. One guy posted here sometime last fall that he had an FT8 station fully scripted, and he just left his PC and radio running, and it called CQ, traded exchanges, and logged all his DX while he was at work, or at class or whatever it was he did during the day.
  10. KX4O

    KX4O Ham Member QRZ Page

    Haha... no not that. We here in Virginia just want to put an automated BBS/Chat system on the air on more HF frequencies in a way that, KK5JY and I agree, is "agreeable" to most.

    Unlike what one might see with the Winlink folks, we are minimalist be design. Our primary doctrine is 97.113(5)...

    97.113(5) Communications, on a regular basis, which could reasonably be furnished alternatively through other radio services.

    Don't get me wrong... there is something to be said for a high speed, high bandwidth signal that passes thrifty messages fast, and then shuts down for hours so as not to be a pest in the bands. I just have a bad feeling human nature will use this speed advantage to encourage less thrifty messaging. We purposely throttle our speed, bandwidth and message size to what we feel is practical for the amateur bands. We may have a minority view.

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