24 Nov 02 2297kHz

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2297kHz 24 Nov 2002.bmp (97254 bytes)

The plot above shows Chirp signals from Inskip, 80km from my location. It shows up a number of characteristics of propagation at 2MHz. The vertical scale is propagation delay in milliseconds and the horizontal scale is UTC.

From the start to around 0500z there are strong returns from the F layer (2.5ms). Up to three hops (indicated by the grey bands at 5 and 7.5ms) can be seen. After 0500, the ionisation in the F layer begins to fall below the level that can support returns until for a short while around 0600, there are no F layer returns at all. The grey band at 0ms at the bottom is probably weak groundwave signals. Just before 0700z the sun begins to illuminate the F layer and the signal returns. However at about 0930z there is sufficient ionisation in the E layer (at about 1ms) to mask the F layer returns. Of course the D layer will be absorbing the signal too at this time. E layer returns continue throughout the day. At about 1500z the F layer returns start again at 2ms and so the cycle continues.

An interesting thing to note is that local sunset time is about 1630, so the D layer and E layer have lost ionisation well before local sunset. DXers on the low bands will be familiar with the fact that DX can be worked before local sunset, this shows why!


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