Tuesday 4 June 2013

First Observations of Ionospheric Scintillation in 4-bit mode

On Monday, we reported about experimenting with the 4-bit mode now available at the station.  This allows us to cover up to 190.6 Mhz of continuous bandwidth, four times the amount available using the usual 16-bit mode.  Of course, the low-band and high-band filters only allow up to 80 MHz of continuous bandwidth in any of the 100 MHz Nyquist zones, but it does mean that we can use mode 357 to cover fully the frequency ranges 10-90 MHz, 110-190 MHz and 210-244 MHz simultaneously.  Also, as reported on Monday, there is an issue with saturation across the peak of sensitivity in the low band.

On Sunday night, we carried out the first ionospheric scintillation (as detailed here) observation of Cas A using 4-bit mode.  To alleviate the saturation issue as much as possible, we used the maximum 8 dB attenuation on the signal.  The results look pretty good:

Looking carefully, you can still see a faint band around the 50-60 MHz range, but the scintillation is still clearly visible across this band.  The data themselves also show some very interesting features in the low band, as shown in the 'zoomed-in' image below:

The image is displayed in grey-scale to bring out the features more.  There is a lot of detail to be analysed in these data, particularly as there is no spacing between subbands in 4-bit mode, making it clear that the 4-bit mode is well-enough suited for these kinds of observations.

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