ALE [MIL-STD-188-141A]: Which one is the best Decoder?

This is an update from my post two days ago. I have expanded the number of test signals and added some hints.

Does your decoder read this track? Buried in noise and plagued by multipath fading, the recordings below will separate the wheat from the whaff.

Often I am asked – and sometimes even asking myself! – “Which one is the best decoder for ALE?” This means: Which one delivers the best decoding under demanding conditions?

To test this, I made a recording of twelve stations “on the air” plus one weak signal, buried in Additive White Gaussian Noise, AWGN. All signals are correctly tuned, no one invers. All were read by at leastby one of my decoders “in a row”.

To test your decoders, you should download this WAV file of 131 seconds length and play it. It can be either directly opened by some decoder, or feed it via virtual audio cable (VAC) into a decoder. I used Audacity for this.

I am as interested in the results as you are – so please drop me a line to dk8ok [at] gmx.net. I like to encourage you to try all ALE decoders you have at hand – the more, the better.

Already the first results were surprising. This concerned both, the decoding ability of the decoders and the repeatability of the test. So far, the following decoders had participated: go2monitor, Krypto500, MARS-ALE, MultiPSK, Sorcerer, and W-Code. Steve, N2CKH, had written some valuable hints to optimize his MARS-ALE software for SIGINT purposes – please see his comment.


This WAV file contains the calls of thirteen ALE stations. Download and save this file (point to the icon, press right mouse button …). Then feed it to your decoders. Copy the results and send them to me. Have fun!

3 comments

  • Hi Nils,

    Good post. Many may indeed be surprised by their results.

    Here I am using the latest build of MARS-ALE v3.00 where of course I configured it for SIGINT analysis verses its normal two-way communications configuration.

    There are actually six 2G ALE emissions contained within the .wav file from six different stations consisting of five soundings and a linking call.

    Both MARS-ALE and PC-ALE can be configured for the best results in SIGINT application to detect and display the weakest signals, to include partial bad data prints if so desired for analysis purposes. I assume most, if not all decoder only tools are so configured, especially those that do not provide the user with access to any such configurations settings. However I have compared some decoders to MARS-ALE and PC-ALE and they do not perform as well when I setup MARS-ALE or PC-ALE for SIGINT application. The MARS-ALE modem has the edge on the PC-ALE modem however, In the case of both tools you want to be using the SYNC display verses the TONES display as there is less negative impact. You also never want to be using any of the TRACE functions as those too add negative loading strain.

    The best settings for SIGINT use of MARS-ALE are:

    FRAME VOTES = 30
    FRAME ERRORS = 3
    SYNC VOTES = 30
    SYNC ERRORS = 2
    DCD THRESHOLD = 0

    Check the boxes for:

    DISPLAY SOUNDS
    DISPLAY BAD DATA
    LISTEN CALLS
    OTHER AUTOFILL
    ALL CALLS
    ANY CALLS
    WILD CALLS

    Do NOT check:

    OTHER STATIC ONLY

    All other ENABLE/DISABLE check boxes are at the users option.

    Regardless of the sound device based decoder tool, one will only achieve the best results with any given tool when a professional grade, low jitter, low noise sound device is used. When its comes to 2G ALE this true but not critical unless one wants to decode signals way down into the noise. It is more critical when it comes to weak decode of MIL-STD/STANAG PSK waveforms.

    In the case of your .wav file, I decoded all six emissions with ease not only using my normal choice of sound device, a $10USD DSP developer board using my firmware, but also the on-board sound device in my laptop as the .wav file was not all that challenging where the DSP board would really be required for single channel analysis,

    Here are the results from use of both devices:
    [ … ]
    By the way the latest MARS-ALE build supports 512 channels overall or in a single scan group where selections of 1, 2, 5, 10 or 20 ch/sec. are provided as well as user selection of any scan rate in between, such as 1.5 ch/sec. for tracking 3G/2G ALE networks. The next build currently being coded and tested increases from 16 to 26 the number of scan groups.

    The latest MARS-ALE can be had for monitoring by anyone interested. I recommend joining the support site for such use at:

    https://groups.yahoo.com/neo/groups/SIGINT_WITH_MARS-ALE/info

    Sincerely,

    /s/ Steve, N2CKH

  • Thanks, Steve, I feel honored to get this comment by nothing less than “Mr. ALE”! Your most valuable hints to check the right things in the options of your software are very much welcome! And your decodings results (here not published, as not to prompt correct results to people who want to crack the stations by their own work …) are a proof of your work. 73 Nils, DK8OK

  • Nils in my opinion Charles Brain, G4GUO is “Mr. ALE” as to PC sound device based software. I am just “Mr. MARS-ALE”.

    As to your latest test2.wav file, a pass at it using MARS-ALE resulted in:

    [here Steve copied the great results he achieved with MARS-ALE and the audio clip. Right now, these information had been cancelled to not cause any bias for other’s tests – DK8OK]

    /s/ Steve, N2CKH

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