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Tyneside, UK
2024 Feb 28
Wednesday, Day 59

Curated by:

Ongoing Observations

For the first couple of days, observations followed a pattern as seen from both Europe by myself and Sven Grahn, and from South Africa by Greg Roberts. From Europe, observations were evening events as Omid went on to make southbound passes across Iran. The view from South Africa came in the morning when Omid was travelling northwards up the east Africa coast and passing over Iran in a northerly direction.

From both locations, Omid was observed to switch on for a Mode 1 type transmission while above the observer's horizon and then, on the following pass, to be observed from horizon to horizon transmitting in Mode 2. Each time Omid was observed to transmit, it went on to pass near or over Iran within a few minutes. Sometimes, though it was very low on the horizon for tracking stations within Iran's borders.

February 5

The routine was broken when Greg Roberts observed the two expected transmissions from South Africa but Europe only saw the Mode 2 transmission, but with a defective signal. This does not mean that the Mode 1 transmission did not occur as it is possible that the onboard timer operated after Omid had passed below the horizon as viewed from Europe.

In this screen capture showing the Mode 2 signal observed from the UK on February 5, the signal is noticeably unstable for a while. At the start and finish of the transit, the Doppler curve is quite normal.

February 6

On February 6, the routine was broken in a different way with no transmissions being detected on passes over South Africa in the morning. However, evening passes continued to be detected over Europe.

February 7

As well as silence over South Africa, February 7 was a sparse day as seen from Europe too. A single observation from the UK saw a Mode 2 signal switch on as Omid headed down towards the horizon at 16:35:23. It disappeared six seconds later as Omid went out of view.

February 8

This day was setting up to be a repeat of February 7. Expectation was that, as well as the silence over South Africa, signals over Europe were unlikely.

The first event was switch on of a Mode 1 type signal at 16:35:23. It switched off 21 seconds later at 16:35:44, taking observers by surprise.

On the next pass, Omid appeared again with a switch-on of a signal with Mode 1 content, followed by switch off about 20 seconds later. This behaviour repeated after 100 seconds of silence. It was soon clear that Omid had settled down to a new routine with a two minute cycle of which 20s was actual transmission. This is now referred to as "Mode 3".

Mode 3 transmissions were subsequently detected over Hawaii and South Africa, showing that Omid's was transmitter was continuously on. For the first time, Omid's transmissions could be detected anywhere on the globe within its line of sight.

February 9

Mode 3 transmissions continued to be detected at all stations throughout the day, its transmitter was continuing to provide worldwide coverage.

The picture above illustrates one of Omid's Mode 3 transmissions. As well as the sidebands, the rapid fading caused, probably by Omid's rotation, is easy to see. It has a main period of 1.75 seconds. Subsequent analysis of the audio by Dick Flagg shows a secondary dip half way between the main peaks.

You can listen to this signal burst here. The 1.75s rotational fade is quite obvious on top of the 1 kHz tone, and the 0.88s dip can be detected too.

February 10

Early morning, Mode 3 transmissions were logged from South Africa on three passes heading northward towards Asia and the Middle East.

European observations again showed Mode 3 as the orbit migrated westwards due to the Earth's rotation. A European pass at around 15:25 UTC was detected from both the UK and Sweden with comments about the signal strength appearing lower than usual. The next pass was unmonitored and Omid's signal then failed to materialise over the UK as expected shortly before 18:30 UTC.

A report from the northern part of the USA showed that Omid was still transmitting at 16:40 UTC.

Checks later in the evening from Hawaii and South Africa confirmed that Omid was indeed off air, having been switched off, or ceased to transmit sometime between 16:40 and 18:25. It's final pass of the day near Iran was between 17:00 and 17:10 at a low elevation.

February 17

As at February 17, Omid was still active though not at all times.

February 19

Reports were received from South America of a weak, intermittent continuous wave signal. It was unstable and contained no data. It was christened "Mode 4".
February 20

Mode 4 signals were received in the UK. They were the last reported signals from Omid and probably represented the end of its active phase.
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