Why is there a frequency slider on the Scan Number graph?

From: Betty Jacobs (betty.jacobs_at_EmailProtected)
Date: Thu Sep 12 2002 - 13:10:12 EST

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    > from Nyima:
    >
    > This graph shows the Received Signal Strength at a particular frequency
    > as a
    > function of Scan Number, so the frequency slider lets you select at
    > which
    > frequency you want to see the Signal Strength as a function of Scan
    > Number.
    > As Scan Number is related to time, it is effectively giving you the time
    >
    > history of Signal Strength at a particular frequency. Ideally the graph
    > would show time instead of Scan Number, but this will have to wait for
    > another release of the software. This plot is useful if you want to see
    > how
    > a signal changes with time. For example, some signals may be present
    > during
    > the day and not the night or vice versa, with the latter possibly being
    > related to ionospheric effects---such as with distant AM radio stations
    > which appear at night.
    >
    > This raises and interesting point that there is a limit to how often the
    >
    > signal can be measured by a scanning receiver as used in the SEARFE kit.
    >
    > The more points in the scan, the less often a particular frequency will
    > be
    > measured. The only way around this is to use a different type of
    > receiver,
    > such as the wide-band receivers used in radio-astronomy. These receivers
    >
    > measure all the signals in a particular band at once. Fast Fourier
    > transform techniques are used to convert the high-speed time
    > measurements
    > into frequency measurements. Either way you can end up with much more
    > data.
    > A receiver of this latter type is being developed at ATNF for site
    > survey
    > work for the SKA.
    >
    > There is similarity with the Scan Number graph and the Scan Number
    > slider on
    > the Frequency graph. On the Signal Strength as a function of Frequency
    > graph, the Scan Number slider lets you choose which scan you want to
    > view.
    >
    > The information in both of these plots are contained in a single plot in
    > the
    > Signal Strength as a function of Frequency and Scan Number plot, either
    > as
    > an image or 3D plot. I've recently noticed that the colour scale on the
    > image plot is not ideal as it does not discriminate between no signal
    > (blue)
    > and signal (very slightly different shade of blue). Chris and Tom may
    > look
    > into this further with their visualisation of the SEARFE data project
    > (see
    > earlier request for data).
    >

    ---------------------------------
    Betty Jacobs
    Community Outreach Co-ordinator
    Faculty of Engineering
    University of Technology, Sydney

    http://www.eng.uts.edu.au/~betty

    Telephone - 9514 2450, Fax - 9514 2611
    Email - Betty.Jacobs_at_uts.edu.au
    Mail - Room 7074 / Building 2 Level 7
    UTS, PO Box 123, Broadway, NSW, 2007

    Engineering Links Project
    http://www.eng.uts.edu.au/links

    SEARFE Project
    http://www.searfe.atnf.csiro.au/
    --------------------------------

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