How to decode HFDL ?


I would like to receive more than one frequency at the same time for decoding the HDFL network.
All of these audio streams are routed to the default audio device that can not be edited in a browser !
Each audio stream must be  directed to a specific decoder.

Thanks in advance for your help.

Gillis of Montreal


  • Hi. Yes, this is an issue that has been mentioned before. The Kiwi server is designed to only communicate with a browser, thus making it independent from any OS. But all browsers we know of route web audio to the default system audio output device. So you can't route different browser audio to different virtual audio channels or even the audio from different windows/tabs within the same browser.

  • Hello

    First, thank you for your reply jks.

    I am very interested in the KiwiSDR, but the impossibility to use more than one frequency at the same time is a real constraint for me!
    I am not a programmer but I read somewhere that in Windows, audio redirection is possible with HTML 5 ?, This audio redirection is technically possible in the browser but not supported for strange reasons especially in a multimedia world ?
    To your knowledge, there is an external application that can do this in Windows ?

    Thanks again jks and good luck with KiwiSDR.

    Loufoque from Montreal.
  • Loufoque,
    I think with some configuration you could use Jack Audio to create virtual audio cables. Then using Pulse Audio you could configure each audio output source to be the "default" each in turn. While the desired audio output was default, start a web browser such as Firefox and the decoder it is to connect to. Then leave it running, and select the next audio source as default and start another instance of a web browser such as Chrome and the decoder it is to connect too. It is a Kludge, but I have it working here with two instances using existing sound cards. I did not configure Jack Audio, which is what would be needed if you don't have multiple sound cards. The system here is openSUSE Linux. See the attached screenshots for proof of concept.
    Ron - KA7U

  • Loufoque,
    As a practical matter, a little google research shows using stand alone applications such as HDSDR or SDR Console and SDR such as SDRPlay, should be the easiest setup. Of course you would be limited to your antenna range. I see,-116.92/4 being a fun site for tracking the planes and no radio required. 

    It would be interesting to learn how you eventually setup your HFDL monitor.
    Ron - KA7U
  • What are you using to decode HDFL ? Can you set different center frequencies ?

    If you can here's a workaround. It involves using the same sound card but spacing the received audio from each SDR instance across the audio spectrum so that the received signals don't overlap each other. Then you can select the audio signal you want to decode by setting the decoder center frequency to pick off the required signals.

    Open up the first instance of KiWi SDR. Tune the signal so that it's at the low frequency end of the decoders range. Set the SDR filter bandwidth (Upper and lower limits) so that it's just wide enough for the HDFL signal. Open the first instance of the decoder and set the center frequency to match the first SDR audio center frequency.. 

    Open up the second instance of KiWi SDR. This time tune to the second signal you want to monitor, but set the SDR center frequency a bit higher and once again adjust the the SDR filter bandwidth (Upper and lower limits) so that it's just wide enough for the second HDFL signal. Make sure there is a small gap in between the first and second signal on the decoder waterfall. Open a second instance of the decoder and set the center frequency to match the second SDR instance. 

    Repeat for a third and fourth instance, or as many as the SDR bandwidth and the decoder center frequency settings will tolerate.

    I hope I've explained this well enough that you can follow what I mean. If you get stuck I'll set it up and take some screen grabs.


    Martin - G8JNJ

  • Update.

    I tried using this method today but I could only fit two separate HDFL signals into a combined portion of the audio spectrum. The limitation is the bandwidth of a HDFL signal and the maximum SSB bandwidth (upper frequency of the passband) that the KiWi will permit.

    In addition to this I couldn't figure out how to setup MultiPSK to utilise different center frequencies, so maybe this method is a non-starter for HDFL. Although I have used it successfully in the past to concurrently monitor meteor pings on five different frequencies using the same WEB SDR.

    It's a pity that the KiWi doesn't have a squelch option that could also be used for SSB signals, as this may be another way of monitoring multiple HDFL frequencies.


    Martin - G8JNJ

  • Hi Martin.

    I am a PC-HFDL user and I can tell you that like Multipsk the center frequency can't  be changed :(  
    It's a great idea that you had. You impress me.
    On my side, i have try a few softwares that pretend to redirect the sound in Windows 10,  but they dont work for me. 
    It's the software, it's me ?  From what i can see it's virtually impossible to reroute the sound from a browswer dans Windows 10 !
    I keep my fingers crossed that this will be possible within Kiwisdr in a near future.

    Thanks for you ideas and your tests. 73

    Loufoque from Montreal.
  • Going back to my first suggestion of how to set this up, I'd use a standard linux OS, open up 4 desktops. Setup 4 virtual audio cables (VAC) using Jack ( ), select one of these VAC as the default audio source, then start a web browser, then start MultiPSK and Pavucontrol. Using Pavucontrol, select the current default VAC as the "recording" source for Pulse Audio. Find the frequency to monitor with KiwiSDR in the web browser. Done with desktop 1.

    Now do the same as above for each of the other 3 desktops. Be sure to select a new VAC as the "default" audio source before opening a new web browser in the new desktop. When you are done, you will be quietly monitoring 4 different HFDL frequencies. 

    Now the sad part of this is what will you want to do with the data from the HFDL output? If you are depending on a Windows program to spot planes on a map, I don't have that solution in mind for Linux as the "hooks" Windows might use to transfer that data between programs is probably not supported in the WINE API in Linux which would be the environment running MultiPSK or other HFDL decoders.
    Ron - KA7U
  • Correction, the aircraft positions are reported correctly using the world map and the local map built into MultiPSK. The ability to use Google Earth or DX Atlas seems to be broken in Linux using the WINE API.
    Ron - KA7U
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