Wednesday, May 8, 2024

TEP signals on the 28 MHz band - 7th May 2024

On the 8th of May 2024, I noticed a distorted QRSS signal on the 28 MHz band. The signal was from FR1GZ on the island of Reunion in the Indian Ocean, a distance of about 10,200 kms from my location.

The image above shows the distorted signal with the carrier spread out over about 6 Hz. Underneath it, I have an image captured a few weeks ago which shows what the normal signal should look like it via F2 layer propagation.

I usually hear Reunion Island on 10m in the morning or afternoon. It was unusual to hear it at 17:50 UTC in the evening time. Evening TEP signals usually peak around 8pm local time. If it was about 18:00 UTC my time and you move further east and add 2-3 hours then the time over some place like Ethiopia is about right.

Considering the timing of the signal and the distortion, I suspect I was hearing the FR1GZ signal via TEP - Trans-Equatorial Propagation.

Normally, evening TEP signals at say 144 MHz cross the Geomagnetic Equator at right angles. However as you go lower in frequency, the requirement for a right angle lessens. By the time we get to 28 MHz, the angles can be close to 45 degrees as shown above.

I suspect that it wasn't 100% TEP either. There was likely some Sporadic-E over Europe for the TEP signal to complete the journey from the Mediterranean area to my location on the south coast of Ireland.

For me, there are two takeaway messages from this...

1) I think the whole TEP zone has a huge impact on signals on 28 MHz and the lower HF bands. TEP is main contributor to propagation on the HF bands and people don't realise it is TEP.

2) The TEP distortion can result in digital signals not being decoded. I think many people fall into the trap of thinking if there are no FT8 signals being decoded then the band in that direction must be closed. It could well be that distorted CW or SSB signals will get through.

That's the beauty of QRSS signals. You can actually 'see' the signal and it gives more clues as to what is happening to the signals on the band.

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