From: George.Warr_at_EmailProtected
Date: Tue Sep 10 2002 - 09:36:32 EST
Hi Betty:
1. Why is there a frequency slider on the Scan Number graph?
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).
2. Is there any way to find out exactly what the frequency is that is giving
a particular signal strength reading?
If you hold down the left and right mouse buttons with the cursor over the
signal strength point of interest in any of the graphs, the coordinates
(i.e. frequency, scan number) of the point are displayed in the top right
corner of the graph. Is this what your questions refers to?
3. Is there any way to have the sound on while the scan is running from the
software. Once I did it and the sound was there but usually the sound cuts
out as soon as the scan starts.
I've asked Oliver about this one and have added it to the list of things to
address in the next release of the software. A quick fix is to turn off and
on the receiver---but this will temporarily interrupt your scan.
Cheers,
Nyima
-------------------------------------------------
Dr. George "Nyima" Warr
Postdoctoral Fellow
Jointly with:
Astrophysics Group
School of Physics (A28)
University of Sydney, NSW 2006
Australia
Tel: +61 (2) 9351 2152
Mob: +61 (421) 476 297
Fax: +61 (2) 9351 7726
email: g.warr_at_physics.usyd.edu.au
and
Square Kilometre Array (SKA) Group
Australia Telescope National Facility
Commonwealth Scientific and Industrial Research Organisation
Marsfield, NSW 2122
Postal: PO Box 76, Epping, NSW 1710
Australia
Tel: +61 (2) 9372 4635
Mob: +61 (421) 476 297
Fax: +61 (2) 9372 4167
email: George.Warr_at_csiro.au
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