Goodbye FT8, Hello Olivia, The MAGIC Digital Mode For HF!

Discussion in 'Amateur Radio News' started by KJ4YZI, Oct 23, 2017.

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  1. KK5JY

    KK5JY Ham Member QRZ Page

    Every base-band data signal has two components. One is the data itself (the high and low bit states), and the other is the clock, which is used to position the bit transitions in time.

    The performance of any digital mode demodulator depends on recovering both of these signals from the incoming signal + noise. If the clock recovery algorithm is good, the data recovery algorithm can be near-optimal in its ability to operate in low SNR conditions. If the clock recovery algorithm is poor, the SNR performance of the data recovery will also be poor, because it will be looking for bit state in the wrong locations.

    This is something that every modem designer has to deal with.

    But the JT-* modes and its various brethren don't do clock recovery -- at all. They depend on receiving clock data directly from the system clock, which must be disciplined to a government station, either via NTP, or hand-synchronization through WWV, CHU, or some other means that is not the radio channel from which the data is being taken. In fact, K1JT called this out explicitly in one of his papers on the subject -- he didn't implement clock recovery. The clocks of the end stations have to be pre-synchronized through one of these methods.

    So whereas demodulators for Olivia, RTTY, PSK, and pretty much every other data mode including CW do the entire task of recovering the signal from the HF channel, the JT modes only recover half (the data), and they must get the other half (the clock) from a non-ham communications channel.

    As a result, there is no way to meaningfully compare the SNR performance of JT65 with any other digital mode, because the JT65 SNR reports are based on the assumption that the JT65 demodulator has perfect out-of-band clock transition information, which artificially lowers the SNR threshold by using the Internet or other means to transfer half the channel data.

    Go read the papers K1JT wrote on the subject. It's very clear. He worked around one of the hardest problems in modem design by simply not solving it at all, and taking that part of the transmission from another communications mode.

    You raise a good point, which is disconnected operation. Technically, this changes nothing, because in order for your modem to work properly, you had to pre-synchronize your local system clock to an NTP, WWV, CHU or other government-sourced clock signal prior to operation, and that one-time act means that you and the other station used a non-ham communication channel to bring your modem clocks into alignment prior to the QSO. Whether your clocks were synchronized during or before the QSO is irrelevant. 100% of the modem clock information was communicated outside the HF channel, and the modem cannot function without this information being communicated in this way.

    Every other digital mode can recover the clock information from the received tones on the HF channel, and their minimum SNR thresholds are dependent (among other things) on the quality of the clock recovery algorithms they use. JT-65 and its siblings cannot, nor do they even try, to do clock recovery, so the reported SNR numbers are artificially optimistic by comparison. And this is why you can't compare JT65 or FT8 SNR threshold values to Olivia. It is at least as different as apples and oranges. It's like comparing an apple to half (at most) of an orange.
     
    KD6SM, KD4MOJ, KK5R and 2 others like this.
  2. KM4CQG

    KM4CQG XML Subscriber QRZ Page

    Eric

    Let me tell you about the advantages of AM Radio and my Johnson Viking !!!!!!!!!!!!!!!!!!!!!!!

    Ian
     
    VK6APZ and K3EY like this.
  3. K3EY

    K3EY Premium Subscriber QRZ Page

    Tinchy pogo
     
  4. KK2DOG

    KK2DOG XML Subscriber QRZ Page

    If I wanted to ragchew I'd get on phone. FT8 suits me just fine.
     
    WU8Y, KM4SLW, K2MOB and 2 others like this.
  5. W0PV

    W0PV Ham Member QRZ Page

    I didn't watch the video either after reading the biased intro text. I have used both modes and have a feel for the trade-offs.

    Glad to see KD6UY call out the erroneous notion that FT / JT modes only send "half the (QSO) data over the radio channel". This seems to be a mistaken "fake-news" type notion that won't go away.

    FT / JT are NOT "half internet" modes, ie, IRLP, EchoLink, or even PACTOR-WinLink. The notion of any "assitance" of the actual data comm'ed over the radio is facitious. It probably originates by the common and widespread use of the internet to set the clock on a home-shack PC to sync FT / JT xmsns. But use of the internet is only one of several available methods to accomplish that task.

    The DX Cluster, email, etc can assists in locating stations OTA for awards hunting and contests. But, if used ethically, it's not communicating OTA QSO data. Of course, there have always been cheaters, even when post-mail was the only way to confirm contacts, and some responsible parties have been convicted.

    Even before the internet made scheduling faster and more convenient, synchronized "blind" transmissions have been used by hams to communicate basic short info on classic modes for decades. Check out how meteor-scatter sequence analog QSO's was / are accomplished. This scheduling and "pre-synchronizing" of shack clocks enables being at the right place at the right time to hear the "pings" and in effect decreasing the perceived SNR. Does this method invalidate those QSO's?

    The non-trivial and highly significant things Joe T. and Steve F. have done is automate the process while adding sophisticated DSP signal acquisition for detection and decoding.

    73 de John - WØPV
     
    Last edited: Oct 24, 2017
    KJ5Z, WU8Y and KN6Q like this.
  6. K3GAU

    K3GAU Ham Member QRZ Page

    I don't know what my favorite digital mode is. I've tried about all of them at one time or another. I just about fall a sleep when listening to, or working, some of the slow ones. By the same token, I don't really get into the real fast ones as there is no way I can keep up with them. My highest typing speed is something short of 30 wpm but at that speed, "The hurrier I go the behinder I get!" :-o

    It seems these days that the less you say to someone the better people seem to like it. The 160 character limit of text messages seems to have everyone in that mind set. If you say anything that takes more than 160 characters, you've talked too long and they want to move on!! :-(

    If your goal is to be anonymous or for a "body count" then FT-8 is your mode. Unfortunately, you never learn anything about your qso pardner other than that his computer works, his clock is about on time and his approximate location.

    When WSJT and its derivatives were invented for use on VHF and UHF for moonbounce or very weak signal work I understood why, but then, it got hauled off to HF. Never understood the need for it there. On most qsos I've monitored both stations were well above the other stations noise level.

    Of the Olivia modes, I like 8-500. It seems to make the most sense to me. It is pretty robust, and yet moves along better than 16-500 that many of the NBEMS nets seem to run and I can keep up with it. Their 16-500 is slow!

    If you want to try something different, try the very old digital mode of Feld Hell or one of the new ARQ modes. To make good use of an ARQ mode requires a different operating technique but it can be fun.

    Just because some mode is old doesn't mean it can't be fun and very useful! Try some of them! :)

    One thing can be said about these days, if you don't like what modes you have, just wait 5 minutes and some NEW digital mode will come along!!

    Dave K3GAU
     
    KK5R and N5ABI like this.
  7. WA4KBD

    WA4KBD Ham Member QRZ Page

    For me, Olivia is just another soundcard digital mode that happens to permit keyboard ragchews, plus you can select speeds/bandwidths that are compatible with your typing speeds and/or band conditions. PKK31 started out as a ragchew mode when I began using it in 1999, but within a few years most QSOs became highly automated and impersonal. The same for MFSK, Olivia, Contestia and all the rest. One can still find some ragchews on these modes, but they are getting harder to find. Hell, I still enjoy Hellschreiber - the original fuzzy mode!
     
  8. W0PV

    W0PV Ham Member QRZ Page

    Obviously the FT / JT automated sync'ed clock modes (includes MSK144 etc) are optimized for passing bursts of short text messages under poor prop weak signal conditions.

    Suitable for awards chasing as defined today, and possibly some contests. Olivia and other continuous text capable modes do have advantages in other contexts.

    Example - it was reported that Olivia was used a bit during the recent EMCOMM crisis due to the hurricanes to successfully send messages with long lists via long-haul HF channels when WinLink / WINMORE protocol failed due to poor prop and weak signals.

    73 de John - WØPV
     
    Last edited: Oct 24, 2017
  9. W0PV

    W0PV Ham Member QRZ Page

    What seems to be another common misconception of FT / JT modes is that they can ONLY send basic QSO info, ie, call signs, signal reports and locations.

    Many either don't know or neglect WSJT also has a seldom used feature called "Free Text Messages". This allows other data to be sent as well, ie, names, greetings and salutations, rig info, etc. "Macros" just like used in other digi modes.

    Of course Free Text Messages in the present design are severely limited to only 13 characters maximum PER XMSN, and other complications. But there is nothing preventing a series of such xmsns to be employed for sending a larger composite text message. It would just take awhile.

    This is one of those trade-offs between FT / JT with sync'ed time-slots and other "continuous streaming text" digi modes.

    73 de John - WØPV
     
    KD6SM, K2MOB and KN6Q like this.
  10. W3SCA

    W3SCA Premium Subscriber QRZ Page

    Umm yeah I wont be saying goodbye to FT8 anytime soon... Worked more ATNO's in the last 3 months than I have in the passed 3 years. Now at 239 confirmed I need all the help I can get!
     
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