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WHY do we need RSID to determine the mode?

Discussion in 'Working Different Modes' started by W0BTU, Jul 5, 2011.

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  1. W0BTU

    W0BTU Ham Member QRZ Page

    Please tell my WHY we always need RSID to determine what digital mode is being received. Can't an algorithm be written to determine what mode and sub-mode is being received?

    This wouldn't work with very weak signals, or on a crowded band (unless we narrow down our passband).

    There are digital signals I can see in the waterfall (wider than PSK31), but so help me, no matter WHAT mode I switch to, all that prints is gibberish. This is nuts.

    Somebody either has software that does this now, or will have.
     
  2. G0GQK

    G0GQK Ham Member QRZ Page

    Well it could be like standing at the side of the road with a bag over your head and guessing which model of car is passing by. Is that engine a Ford, a Peugeot, a Nissan, Toyota, Suzuki, Honda, Citroen ? Get the drift ?
     
  3. W0BTU

    W0BTU Ham Member QRZ Page

    I don't think that's a good comparison.

    From what I see in my waterfall, I'm convinced that the right software algorithm can determine at least some digital modes. Once that happens, the software could automatically switch to the correct mode.

    Each mode has multiple tones of a fixed duration of a spaced by a fixed amount. I've written enough software to know that an algorithm can be written to determine:

    How many frequencies (tones) there are in the passband
    What the duration of the tones is
    What the spacing of the tones is

    and figure out the mode from that.
     
  4. NN4RH

    NN4RH Premium Subscriber QRZ Page

    Isn't that basically what RSID already does?
     
  5. W0BTU

    W0BTU Ham Member QRZ Page

    The problem is RSID is that it's off by default, and I seldom see a signal with it turned on.

    Even when it's enabled, it's only sent occasionally.
     
  6. VK2FAK

    VK2FAK Ham Member QRZ Page

    Hi all...

    The thing about the RSID is that it can tell you if a signal is on your waterfall that you may not be able to see yet...

    Last time I looked the RSID had a S/N of something like -25....which is way better than all the Normal Digital Modes.........example is Olivia....I have had 100% copy on a signal I could hardly see on the waterfall....so without it I would not have known it was even there..

    people wonder why they don't make a contact......turn the RSID on...its there use it....for psk31, RTTY. tick the box so those modes dont trigger the RSID.....but all others do


    John
     
    Last edited: Jul 6, 2011
  7. AG6WT

    AG6WT Ham Member QRZ Page

    Theoretically it is possible to identify and decode an unknown mode without a RSID. However, decoding does take some CPU power. When you tell the computer to scan the entire bandpass looking for signal and to decode it using all possible digital modes you'll quickly tax the computer to the point where it can't keep up with the data streaming on the waterfall. There are more than 100 distinct digital modes.

    RSID was designed to make this problem somewhat tractable by pre-pending the unknown digital mode with a well defined digital signature. The RSID is a MFSK transmission with a fixed length and bandwidth. The problem then is small enough for a computer to do a brute force search through all valid RSID possibilities.

    Assuming your software understands the digital transmission that you can't identify, it is possible that it is a mode that requires both the sender and receiver to be using the same sideband, e.g. USB<->USB or LSB<->LSB. For example, with PSK31 it doesn't matter if you are using USB or LSB, however, with QPSK31 is does matter.

    See if you can take a screen shot and post it here. It's quite likely some will know what it is.
     
  8. W0BTU

    W0BTU Ham Member QRZ Page

    I'm not asking for that capability, though it would be nice.

    In every case where I was trying to determine the mode, there was only that one unknown mode in my passband.

    Like I said above, The problem with RSID is that it's off by default (at least in Fldigi), and I seldom see a signal with it enabled (READ: almost nobody uses it!

    And even when RSID is enabled, it's only sent occasionally.

    This means that RSID is effectively almost worthless!
    There's GOT to be a better way.

    I have tried switching sidebands, but I usually leave it at the band's default. Why would anyone not use the band's default?

    There's this page, but every time I page through it, the signal is gone before I can find a picture that looks like the signal on my waterfall. http://www.w1hkj.com/FldigiHelp-3.20/Modes/index.htm
     
    Last edited: Jul 6, 2011
  9. AG6WT

    AG6WT Ham Member QRZ Page

    I think the reason RSID is disabled by default is that some ops who use it leave it on during the entire QSO. You only really need it when calling CQ and then only with one of the more esoteric mode. There are more than a few people who leave it on when using PSK31, and of all the possible modes, that is one where you don't need RSID. The problem is not RSID but rather poor operating practices.

    As to why someone would not use the band default on selecting USB vs LSB, as far as I know, the selection of which sideband is not determined by the band like in phone communication (i.e. phone on 40m is LSB, 20m is USB) but rather by mode. For example, PSK31 is traditionally USB on all bands, RTTY is LSB.

    The fldigi link to how different modes look and sound is helpful but not complete. There are other modes that occasionally pop up that are not represented there. SSTV, PACTOR, AMTOR, G-TOR, PACKET, and Clover come to mind. And JT65 but one that is easy to recognize. It is quite possible that the operator of the unknown mode you are seeing knows about RSID but isn't using software or hardware that supports it.

    What exact frequency are you seeing this signal and how wide is it?
     
  10. W0BTU

    W0BTU Ham Member QRZ Page

    I really don't remember the frequency or bandwidth, sorry.

    I'm not blaming RSID per se or suggesting that it be eliminated. I'm just saying it would be nice to tune to a non-PSK31 signal on a waterfall and be able to decode it in less time and with less hassle.

    I'm hoping that if this thread doesn't motivate someone to write a mode detection algorithm, then enough people will petition some programmers who will.
     
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