ad: Amateur-1

New Digital Petition at the FCC -- RM-11831

Discussion in 'Ham Radio Discussions' started by K0IDT, Mar 31, 2019.

ad: L-HROutlet
ad: l-rl
ad: Left-2
ad: Subscribe
ad: DLSpec-1
ad: Left-3
ad: L-MFJ
ad: MessiPaoloni-1
  1. KA9Q

    KA9Q Ham Member QRZ Page

    Glad we agree on something!
    Actually, it applies to every mode; it's just that it's only one metric of many. But your point is well taken; instead of "spectral efficiency", I should have I said "the efficient use of the radio spectrum". Other important metrics include transmit power, where that power goes, how long I must transmit that power, and how wide an area must be cleared of other transmitters around my intended receiver to protect it from harmful interference. All expressed as "per unit of user data transferred".

    This is why "spread spectrum" can sometimes be more efficient than narrowband modulation, why error control coding (both FEC and ARQ) are so important, why automatic transmitter power control is seriously underappreciated...and yes, why source coding (aka data compression) is important.
    You're right, the proper measure is in fact the "goodput" -- how much user data actually gets through for a given amount of interference to other stations. I notice you didn't mention P4; while I am not familiar with every one of its modes it does seem to be designed to "shift gears" over a wide range to adapt to channel conditions. Many other modes, e.g. FT8, do not have any kind of gear-shifting ability and rely totally on a human operator to know when to give up and switch frequencies and modes. Adaptation to changing conditions is still one of those incompletely solved problems where ham radio can offer something to the state of the radio art.

    No, speed is important because you need to normalize everything to the total amount of user information being transferred. The JT modes are very well designed to operate over very poor channels, but their throughputs are severely limited even on excellent channels. The inability to take advantage of improved channel conditions, if only by decreasing transmitter power, is itself very inefficient use of the radio spectrum.

    Regarding channel sharing, you are referring to the "multiple access problem". A lot of progress has been made here, including by yours truly; an algorithm called MACA that I invented specifically for ham radio found its way into standard 802.11 WiFi. Spread spectrum can be used for multiple access; the technique is better known as Code Division Multiple Access or CDMA. It's one of the reasons why spread spectrum can actually be more efficient in practice.
    Last edited: Jun 12, 2019 at 10:15 AM
  2. KA9Q

    KA9Q Ham Member QRZ Page

    As I've already said several times, I don't like proprietary stuff on the ham bands but the best response is to beat it at its own game. You'd be surprised at how often even a black box can be a useful reference point for further experimentation by showing what's possible (even if they don't show exactly how) and inspiring and challenging you to do it better and/or more cheaply and/or in a more open fashion. (Remember what was often said early in the cold war: that the only "A-bomb secret" was the fact that it was possible. And we gave that one away in August 1945.)

    This has happened to me more than once in both my professional and amateur career. It also spurred VK5DGR to invent CODEC2 and make it freely available to hams as open source. Remember, everything you say about Pactor4 applies equally to DVSI's ABME codecs in DMR/D*Star/Fusion, so again I have to ask you if you're prepared to take on the whole amateur digital voice community. From what I can tell, it seems much larger than the amateur Winlink/Pactor community.
  3. SM0AOM

    SM0AOM Ham Member QRZ Page

    This was one of the major aspects when developing the Canadian Marconi/Sundstrand Data Control system specification in the late 80s for the HF datalink system that eventually evolved into the ARINC 753 "air interface".

    Early, it was decided to take advantage of adaptive data rates and compression in order to utilise the scarce resource of aeronautical HF spectrum as good as possible.

    One goal of the whole project was to increase the effective throughput of status messages and position/weather reports by a factor of at least 10 compared to voice using the same spectrum space and permissible message latencies. In practice, a "trunking factor" of over 20 could be observed.

    HF represents a very special case of "multiple access problem", where skip zones or interference may mask transmitters in the relative vicinity of a receiver. Also, asynchronous access methods often do not make good performers on HF.

    The state-of-the-art regarding HF modems and waveforms has advanced tremendously in 30 years and with the easy and cheap availability of GPS derived UTC time-scales the synchronisation problem has become much easier to solve.

    Spread-spectrum is also an hitherto comparably unexplored way of channel coding which could present interesting and potentially high-performance system solution when implemented through SDR techniques.

    It would be a pity and a large step backwards if provincialism and nearsightedness would deprive amateur radio of being part of the evolution of high-performance HF
    data transfer systems.

    KA9Q likes this.
  4. N8OHU

    N8OHU Ham Member QRZ Page

    What the whole problem here is is that nobody has produced a compiled executable that people can run on their computer to attempt to decode the compressed data being sent. It doesn't seem to matter that the compression method and how to use it in Ham Radio is very well documented as well as having multiple open source implementations (Winlink would not be usable on Linux now if there weren't any), which seems to be deliberately ignored every time it's brought up.
  5. KX4Z

    KX4Z Ham Member QRZ Page

  6. KX4Z

    KX4Z Ham Member QRZ Page

  7. KX4Z

    KX4Z Ham Member QRZ Page

    How many years has it been claimed that the security of 300+ million Americans is endangered by the existence of these systems, used by several different groups?

    How many years does it take for a skilled electrical engineer to take existing code and turn it into a slightly different project?

    How many degrees does it take for one to understand how to combine packet streams?

    Could we have a list of all the experts who have educated us on this from their repository of scores of years of brilliance?

    Where have these experts been? The whole free world is tottering—- teetering in the balance because of this security threat!

    Why the entire government should come to a complete halt so that more resources can be poured into making small adjustments to this source code.... so we can protect Americans.

    And who knows, perhaps all of Europe is threatened as well?
  8. KX4Z

    KX4Z Ham Member QRZ Page

    Away with contests, stop the American radio relay lead, cease publishing of these journals, no more FT8, stop building new protocols! everyone must pour their full attention into saving humanity.

    Why, oh why have so many wasted so much time? When such a huge effort must be accomplished immediately. It’s not the future of ham radio, it’s all of our nuclear secrets, it’s our icbms , carriers— all the corporations! Why the free world is at stake.

    How can it be that so many brilliant people have not succeeded at this task in so many years? Where was their error, where was their mistake?
  9. KX4Z

    KX4Z Ham Member QRZ Page

    Oh, I forgot. It’s impossible.
  10. K0IDT

    K0IDT Ham Member QRZ Page

    Probably, what's your point?

Share This Page