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Sporadic-E propagation, which is caused by the ionization of the ionosphere at around 90-120 km altitude, is most common between the summer months of May and September in the northern hemisphere, and October to March in the southern hemisphere, during daylight. Openings can also occur at other times, day or night. It’s also possible for the muf* to rise high enough for F-layer propagation at these frequencies, but this is more rare. Fuller explanations for the reasons behind these forms of propagation can be found elsewhere on the internet.
Below are various, and sometimes unusual examples, as seen by my spectrum analysis of the 48.250 and 55.250 MHz TV channels in Europe.
*muf = maximum useable frequency
July 07 2005 0700-0800 utc
A full-blown sporadic-E opening in progress. Seven or eight transmitters can be seen, along with all their associated 50Hz hum bars!
Jan 17 2004 1300-1855 utc
Portugese transmitter on 48.250450 MHz, drifting. Oscillation period approx 45 minutes.
A ten minute plot of the same opening, including the signal from the Liege, Belgium transmitter on 55.250044 MHz at the top.
Strange intruder on Channel L3? Read on…
Above are two consecutive one-hour plots of activity from 12 June 2006, 10 to 12 hours UT.
In each image, the top half is French channel L3, the bottom half is European channel E2. L3’s frequency is 60.500 MHz. The L3 transmitter is on 60.500 MHz exactly, and should be the only occupant of this frequency. It is located at Carcassonne, in SW France, at 143° Azimuth and 940 km distance.
On channel L2 “normal” meteor activity can be seen (short vertical lines). Starting at 10:10 UT, sporadic E can be seen as a the slightly wobbling signal which is slowly descending in frequency. A lower 50 Hz timebase line appears at around 10:18 UT, proving that the signal is not American in origin. Sporadic E on channel E2 kicks in around 10:30 UT. The sporadic E signal on L2 continues to drop in frequency until 11:20 UT, when it suddenly decides to whizz upwards at a rate of knots (manual correction to the transmitter?)
Where is this extra signal on L3 coming from? Carcassonne, according to TV-List, should be the only user on 60.500 MHz. Another French channel is resident at 60.5312 MHz at Besançon/Lomont. Did this drift down? Or could it be a rogue from channel E4 at 62.250 MHz, possibly a badly maintained TX in Africa? The wobbly signal could indicate either a poorly maintained transmitter, or a difficult and long propagation path, or both.
The signal has also appeared earlier on 09 June 2006, leading me to think that this is a serial drifter….
An intermittent sporadic E signal also appeared on 03 June – the first day I started to monitor this frequency, off-frequency by -20 Hz from the nominal 60.500 MHz…
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