internet lag and decoding JT65

I have been using the various kiwisdr sites on the internet and using them as "target practice" for decoding various digital modes.  Chipping in to help fund the spread of the kiwisdr network was a no-brainer for me, and I'm glad to see the project succeeding.

Anyway, here is my problem.  JT65 (and related) are transmitted on a fixed one minute schedule, and synchronization needs to be within about a second, otherwise the decoder will fail to work at all.  When I try to listen in on jt65 transmissions, I'm seeing lag of more than five seconds.  The decoder (wsjt-x) refuses to decode anything as a result.

Does anyone have a suggestion for how to decode JT65 via a web-based kiwisdr?  I suppose I could record the audio to a .wav file, then play it back later, aligned such that the JT65 sequences begin at the top of a minute, but that is less than satisfying.


  • I'm using cell phone internet from Phoenix, AZ, USA and connecting to my kiwiSDR which is located in eastern Oregon and connected to a wireless ISP As you can see from the images attached, JT65 is being decoded just fine over the web. I'm not seeing 5 second latency though. I don't think I've ever dealt with 5 second latency on the Internet, except for satellite connections, and even then, it was more like a 1.5 seconds.
    Ron - KA7U

  • Sorry, poor screenshot of the KiwiSDR desktop. Here is a better one.

  • Ron / KA7U, thanks.  I was using the WSJT-X decoder and apparently it is more strict about timing. I installed multipsk and it does decode JT65.  Interestingly, it seems to decode only one JT65 transmission per minute, while the WSJT software decodes all jt65 signals in parallel.  Maybe multipsk can do it too, but I haven't spent enough time with it to know.

    The JT65 spec says, "A transmission nominally begins at t=1s after the start of a UTC minute and finishes at t=47.8s."  I am hearing transmissions start at 8s after the minute, so I am 7 seconds off! Although I have a reliable, fast internet connection, comparing my phone's time vs that of my PC, there was a 6-7 second discrepancy.  It turns out the nist time server my PC was configured to communicate with has been unreachable for a few days so my PC's time has drifted. Changing the time server and resync'ing has fixed my problems.
  • I am new to this forum but have been listening to KiwiSDR receivers worldwide and compared their performance to the other online SDR systems.
    RF performance of KiwiSDR is good.
    Therefore have to have answers to some questions before considering the possible purchase of the KiwiSDR.
    The basic idea is to install the remote receiver in the quiet rural area for serious low band DX and contest work for our club members.
    1.  Can KiwiSDR be used without the Beaglebone card but different computer that has much more processing power? Are there interface solutions to do this?
    The major problem, that I have found with almost all KiwiSDR/Beaglebone combo installations is audio and waterfall lag. Compared to the WebSDR and  RemoteSDRClient systems it is generally 2-3 seconds at the beginning and increasing up to 7-8 secongs in the long run. This makes KiwiSDR/Beaglebone combo useless foe contest/DX work. On the other hand good WebSDR system's lag is around 500ms and constant. I wonder if the receiver itself, beagle card or OpenSDR software is responsible for this. Did anyone tried to use  KiwiSDR with different computers, different SDR software and what were the time delay results?
    Thanks in advance,
  • jksjks
    edited December 2016
    1. No, the Kiwi was not designed to be an SDR that supplies a wide-band digital IF to the Ethernet or USB like other traditional SDRs. It is a "shortwave receiver" class of device that is meant to work as a self-contained appliance. But the question remains: is it possible? What might the largest possible bandwidth be? The trouble is that the interface between the FPGA and the Beagle is a 48 MHz SPI (serial link). There is no direct connection between the FPGA and the Ethernet or USB on the Beagle. That plus the latency problems of running the samples through the Linux networking stack make it uncertain what the ultimate performance might be. You would pretty much have to do a proof-of-concept effort and just see what bandwidth result you get. A good project for someone! But not us (at least not at this time) because we are completely underwater working on improvements to the existing software.

    This FAQ discusses the related question of why there are only 4 channels and not 400+ like WebSDR:

    2. You should not be seeing delays increasing to 7 or 8 seconds. Something is not right. Yes, the delay with WebSDR is around a half second. Ours should be 1 to 2 seconds. But not above that unless there are other issues (Internet, browser, etc.)

  • jks, I already fixed my problem (see my comment from Dec 24). My internet time server was down and so my PC time had drifted.  I pointed it at another time server and things are good now.  Thanks.
  • Hi. My last response was to us5we who added a comment to this thread today (probably should have started a new thread).

  • I am not sure about it
  • KiwiSDR nice SDR
    It not similar to all  and have many features - no prob decode JT65 - just  default do VAC

  • yes , delay KiwiSDR 1-2 sec  can it be less?
  • Agood power supply, reducing latency by 500-600 msec and from the router 1A it bad 
    but As well linear PS 2-3A
  • edited March 2017
    On my local connection I'd estimate that the KiWi lag is only about 200-500mS maximum. 

    Just about a long enough a delay to cause you to hesitate whilst speaking if you are monitoring your own transmission.

    Over the internet the delay can be much longer, one user has reported a delay of around 2 seconds. 

    I think a lot depends upon variables in the users ISP and network routing, all of which are outside the Admins control.


    Martin - G8JNJ

  • What you speed Inet??

  • Hi Serge,

    Not that good :-(

    Down 12.45 Mbps
    Up 0.45 Mbps
    Ping 25.25ms


    Martin - G8JNJ

  • Hi Martin ,
     oh  yes  my high 70/60 mbit sec  but delay  1-1,5 sec
     but ping 100 msec 
    I saw you antenna  work FB!

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