G'day All,
Alberto's excellent Argo program displays 320 (?) spectral lines each spaced
by a frequency which is the reciprocal of the FFT record length in seconds.
The record length appears to be a power of two in terms of number of samples
(requirement for the simplest FFT algorithms) at a sample rate of 11025Hz.
So for Argo mode of 10 seconds it appears that the record length is 11.89
seconds which gives a spectral spacing of 0.084 ... Hz. This times
320 gives a displayed bandwidth of about 27Hz. At 30 seconds this same
analysis gives 6.7Hz, 60 seconds -> 3.36Hz, 120 seconds -> 1.7Hz. Other
dot settings go for the nearest power of two (e.g., the 90 second dot
setting uses the same resolution as the 60 second dot setting).
So the bandwidth displayed on the screen is forced by the spectral spacing
(determined by the record length) and the number of pixels available on the
screen. Why 320 lines ?? Well, for 640 x 480 resolution (480
vertically) that is approximately what is left over after space is taken for
menu bars and status lines. The only way around this would be a version
for a screen resolution of 1024 x 768 (which would widen the bandwidth at 60
seconds dots from 3.36Hz to about 6Hz, for 120 second dots - from 1.7Hz to
about 3Hz) or to swing the spectrum display around by 90 degrees to take
advantage of the wider pixel dimension in the horizontal direction. Of
course this would limit the length of time available on the screen.
There would need to be extra CPU overhead to display the extra information
(but I think not to do the FFT assuming a standard algorithmn is used) and
this may be a problem for slower machines. Not to mention a considerable
slice of Alberto's time to implement.
In any case, if the above gains are considered significant we would need to
ask Alberto to consider it. I am not going to do that as I have already
used up my share of Alberto's good nature asking him for other enhancements
in the past :-)
73s Steve Olney (VK2ZTO/AXSO - QF56IK : Lat -33 34 07, Long +150 44 40)
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HomePage URL: http://www.zeta.org.au/~ollaneg
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