NOAA FAX

KA7UKA7U
in Signals Received
I find that if the computer is only receiving a FAX and other operations are not concurrently running, the FAX received is synchronized, but if other operations are concurrent, then the image is disjointed. This FAX was received in less than optimal conditions and yet it stayed syncronized as I did not have other operations on the computer during reception.

Ron - KA7U

Comments

  • jksjks
    edited May 2017
    Which computer? Computer running browser or Beagle? Can you define "other operations"?

    The Beagle is only meant to be running the Kiwi server and nothing else. There are critical realtime constraints that require Linux to get-out-of-the-way as much as possible.

    On the client computer if the browser/javascript doesn't get the required realtime response to keep up with the audio output demand then you'll drop audio samples and the fax will get shifted. This can be improved by making the Kiwi audio buffer in the browser larger. But then the latency gets longer, and a different group of people get upset with me, lol.

    KA7U
  • KA7UKA7U
    John,
    I did not write this very well. Sorry. 
    I'm talking about the client computer. Other operations mean just about anything from having a mouse moving to open a tab on a web browser to scrolling down a page in a word processor. Generally I find that just leaving the computer alone while the FAX is receiving gets the good results. The computer here is briefly described in this file: http://ka7u.us/stuff/info.txt .  

    The software is described as:
    linux-vxyy:/home/ron # cat /proc/version

    Linux version 4.1.39-56-default (geeko@buildhost) (gcc version 4.8.5 (SUSE Linux) ) #1 SMP PREEMPT Mon May 1 04:41:25 UTC 2017 (5f
    49ec2)


    For whatever that might be worth. I find this generalization to be true on all of the computers that I use Multipsk to decode a FAX from the KiwiSDR, or other VoIP sources such as IP-Sound.

    Just stuff to know about, I think.
    Ron - KA7U

  • jksjks
    Well, timely that you should mention this issue. There has been a similar complaint over on github issues having to do with fax reception: https://github.com/jks-prv/Beagle_SDR_GPS/issues/97

    To help diagnose timing issues in general, and also have a little fun (which has been in short supply lately), I'm in the middle of writing a new extension shown below. It's just barely starting to work. Lots of problems. Zero features. But it should be very useful. Fax reception seems to be especially sensitive to sample dropouts, sample rate errors, etc.


    image

    Attachments:
    https://forum.kiwisdr.com/uploads/Uploader/53/63d04ecc9234c601e2f831a3dc090e.png
  • KA7UKA7U
    John,
    Interesting discussion on github. Over my head for sure, but still I get the idea of it. Once your extension can save the image to a file, it will be great. I'm not sure how many options it might need, but I think setting it to monitor and download / save the images, would be nice.  Your image looks better than what Multipsk or FLDIGI is currently producing, or maybe it is because you are tuned to a cleaner and stronger station than I've been listening to.

    Thanks,
    Ron - KA7U
  • jksjks
    Because reception of HF fax is poor here in New Zealand I've had to use one of the Kiwi beta sites in Europe to get strong reception of DDH3 & DDK3/6 out of Germany. That image has contrast problems. It should be a well defined black & white. The open source fax code I found is kind of strange. I don't really understand it yet. Especially the FM demod section.
    KA7U
  • G8JNJG8JNJ
    edited May 2017
    Hi John,

    I can confirm the following as being active FAX stations, all of which I have received and decoded using MultiPSK via my public KiWi (and which have been tagged) over the past six months or so.


    All frequencies are for USB with the exception of Murmansk.

    Frequency MHz Callsign Location Notes
    3.853 DDH3 Pinneberg / Hamburg, Germany DWD, FAX
    4.2331 NMF Boston, Massachusetts, USA Daytime 4Kw
    4.61 GYA Northwood, UK F1C-120 weather fax
    5.0981 VMC Charleville, Australia All times 1Kw
    5.753 VMW Wiluna, Australia Daytime 1Kw
    5.7535 VMW Wiluna, Australia Nightime
    6.33 Murmansk Meteo Murmansk, Russia LSB
    6.3385 NMF Boston, Massachusetts, USA All times 4Kw
    7.5331 VMW Wiluna, Australia All times 1Kw
    7.7945 JMH Tokyo, Japan FAX/120/576
    7.8781 DDK3 Hamburg / Pinneberg, Germany 20Kw
    8.0381 GYA Northwood, UK Anytime 10Kw
    8.105 SWA/SVJ4 Athens, Greece Hellenic Meteorological Service 8Kw
    8.4656 JJC Kyodo News Agency, Japan 10Kw
    8.502 NMG New Orleans, USA All times 4Kw
    8.6801 NMC Pt. Reyes, California, USA All times 4Kw
    9.1081 NMF Boston, Massachusetts, USA All times 4Kw
    10.5531 VMW Wiluna, Australia All times 1Kw
    11.028 VMC Charleville, Australia All times 1Kw
    11.0846 GYA Northwood, UK Daytime 10Kw
    12.7436 JJC Kyodo News Agency, Japan 15Kw
    12.7481 NMF Boston, Massachusetts, USA Nightime 4Kw
    12.788 NMG New Orleans, USA All times 4Kw
    13.8806 DDK6 Hamburg / Pinneberg, Germany 20Kw
    13.9866 JMH4 Tokyo, Japan All times 5Kw
    15.6135 VMW Wiluna, Australia All times 1Kw
    17.06765 JJC Kyodo News Agency, Japan 15Kw

  • jksjks
    Hi Martin,

    That's very useful -- thank you. I added some menus to the extension recently, with fax station preset frequencies. But wasn't really sure how many of those were active. I found this list helpful: http://www.nws.noaa.gov/os/marine/rfax.pdf

    Also some of the individual meteorology services publish detailed schedules for those stations that don't transmit continuously: http://www.bom.gov.au/marine/radio-sat/radio-fax-schedule.shtml
    I'll try and add direct links to those in the extension.


  • G8JNJG8JNJ
    Hi John,

    OK no probs.

    Send me a PM if you want to use my second (non public) KiWi to test the FAX extension.

    Regards,

    Martin


  • G8JNJG8JNJ
    edited May 2017
    And another two confirmed today.

    16.9691 USB JJC Kyodo News Agency, Japan 15Kw
    17.4281 USB 9VF/252 Kyodo News Agency, Singapore 0740-1010 1415-1815 10Kw

  • KA7UKA7U
    John,
    You must have been making great improvements to the FAX extension. This image is a partial but it shows up straight. The shift click works to align OK too.
    Ron - KA7U


    Attachments:
    https://forum.kiwisdr.com/uploads/Uploader/08/263408537f880e08a1c5560056d005.png
  • jksjks
    Yes, the v1.100 release improved the situation. Details here: https://github.com/jks-prv/Beagle_SDR_GPS/commit/ba3ec102465bfe29d8a6582cb4068ba4c8dbe700

    WA2ZKD
  • f1jekf1jek
    +1000 on my side about the new fax extension improvements ! 
    On 13382MHz, the result is close to perfect.

    Thanks a lot.
  • WA2ZKDWA2ZKD
    a thought on the menu....    3 pulldowns

    - region
    - TX QTH
    - Frequency

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