New signal in US on 27.2 kHz - TACAMO?

edited March 2021 in Signals Received

I happened to be looking at (my noise floor) on VLF when a new signal popped up on 27.2 kHz. It literally popped up, taking about 3 seconds to reach full power, making it #2 on VLF in Colorado, US.  It was big, digital but not QPSK, although there was coherence with QPSK and the IQ decoder.

I went to TDoA and found some stations that could hear it and ran an analysis - a bit east of Hot Springs Arkansas with pretty good definition.

I checked with a Missouri SDR (not listed), thinking it would be loud at his location only to discover that it had stopped transmitting.

I've never seen this before, either the modulation nor the carrier coming and going. It isn't listed on my default Kiwi labels.

Is this a known station that only transmits occasionally?

Since writing this I've had it suggested that what we are hearing is TACAMO. If so, it may be an airborne 200 kW transmitter into a 6 mile long trailing wire antenna!

If so, no wonder it is a big signal!

Glenn n6gn


Glenn n6gn


  • Glenn,

    I checked on it and it is faint but visible on the waterfall here at ka7u. A serious broadband noise consisting of spurs showed up about 5 minutes ago and I have no idea where that came from either. First time I've seen it here. We are having serious wind, so the power line might have taken a hit somewhere.

    Ron - KA7U

  • jksjks
    edited March 2021

    Do you have any waterfall/spectrum/iq_display screenshots?

    The only thing new I've noticed is CKN 76.2 Matsqui, CAN (Vancouver area) being back on, which it does from time to time.,+BC,+Canada/@49.1073402,-122.2429601,943m/data=!3m1!1e3!4m5!3m4!1s0x548673f143a94fb3:0xbb9196ea9b81f38b!8m2!3d49.2827291!4d-123.1207375

  • jksjks
    edited March 2021

    Also what might be CFH Halifax, CAN on 133.15 which I had not seen before. QPSK, extremely strong on the US E. coast. TDoA was inconclusive due to poor geometry of sampling stations (probably).

  • Was watching a new signal on 29.4 and it suddenly went off. I selected the 160 button to help clarify the signal in the display, that changed the mode to AM. So not sure what goes on with those buttons to the right of clear. Actually not certain about most of this mode extension. Interesting though.

    Ron - KA7U

  • The 2.4k/160/40 buttons are leftover from early development when the IQ display extension was used to measure VLF station carrier drift when GPS correction of the ADC clock was first operating. A number of bugs were found and fixed using it. In those days you couldn't simply type "/nnn" into the frequency box to set the passband width. And the IQ display always needed AM mode. So that's why the buttons switched mode as well. This was long before Christoph added the PLL which needs IQ mode selected.

    So, as with many things, it needs to be revisited.

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