FT8 Decode EOT Jack Hammer Sounds

Discussion in 'On-Air Operations - Q&A' started by N2CG, Aug 12, 2018.

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  1. N2CG

    N2CG Premium Subscriber QRZ Page

    Greetings Fellow FT8 Ops,

    I've been operating on FT8 mode for the past nine months. Beginning about 2-3 weeks ago I started hearing "strange" (for lack of a better term) FT8 decode end of transmission (EOT) sounds.

    Depending on the audio range of the FT8 signal being received these EOT's mimic what sounds like a jack hammer, a Jake brake or a machine gun with 8-9 rapid successive bursts! On a very busy FT8 mode band like 20m, it's almost impossible to identify for sure which station is using this FT8 decode EOT jack hammer sound.

    Are other FT8 ops also hearing these decode EOT jack hammer sounds? Are these sounds intentional; and if so what useful purpose do they offer?

    73, George N2CG
    AD8BU likes this.
  2. AD8BU

    AD8BU Ham Member QRZ Page

    I personally haven't heard it on the FT-8 frequencies, but what you describe sounds like an over the horizon radar, commonly known as a "Russian Woodpecker."

  3. AD8BU

    AD8BU Ham Member QRZ Page

    Here's a better example than the one above:

  4. N2CG

    N2CG Premium Subscriber QRZ Page

    Thanks Frank AD8BU for your recent two replies to my Initial post asking about FT8 Decode EOT Jack Hammer Sounds on this QRZ.COM On-Air Operations - Q&A forum back on August 12, 2018.

    After several weeks of not receiving any replies to my QRZ.COM post I joined the FT8-Digital-Mode@groups.io group and posted the same inquiry. Soon after I started receiving replies from several ops like you who also believed these Jack Hammer sounds
    were caused by Over The Horizon Radar (OTHR).

    I viewed and listened to the two YouTube videos you posted above and the OTHR in these videos sounds exactly like what I heard on the decode EOT FT8 signals.

    The good news is that since I originally posted my inquiries here on QRZ.COM and on the FT8-DM group; I haven't heard the Jack Hammer sounds on FT8 frequencies in over a year!

    So, if these Jack Hammer sounds were in fact caused by OTHR; then I’m guessing either the OTHR transmissions have stopped or too weak to be hard at my QTH; or the OTHR transmitter control station(s) have notch out the OTHR transmissions on Amateur Radio frequencies.

    73, George N2CG
    AD8BU likes this.
  5. AD8BU

    AD8BU Ham Member QRZ Page

    Cool, I'm glad you didn't have to wait over a year for an answer. That being said, I will sheepishly admit that I didn't realize how old your thread was when I first replied... :oops:

    I have heard them a couple times when I was listening in on a web based SDR back in the spring, but I haven't heard them on the FT-8 frequencies.

    Fun fact: The Kenwood TS-940S has a noise blanker specifically for OTHR interference, and mentions the "Russian Woodpecker" by name in the manual. I haven't had to try it out yet, though. :D
  6. KP4SX

    KP4SX Premium Subscriber QRZ Page

    There's an OTHR transmitting site a couple miles to the west of me. They used to make quite a bit of racket across the bands. Now they seem to just send an occasional burst of about 0.5 sec on random frequencies and I rarely hear them.

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