Von:    Alberto di Bene, INTERNET:[email protected]
An:     "'Geri' Kinzel, DK8KW", DK8KW
        

BE:     Re: Spectran Beta 2c


Hello Geri,

             yes, there is an answer to your question about the 'fuzzyness' of 
the
display.
It all boils down to how Spectran works, and the 'hidden averaging' it does on 
the
received signals. I enclose here following an explanation I gave to Rex Moncur 
about
this subject. He was asking me if/how Spectran does perform an averaging on 
what it
receives. What happens in your case is that when your CPU is more loaded, the
overlapping  factor (defined below) decreases, and with it the 'fuzzyness'.
Feel free to post this message to the newsgroup you mention.

73s
Alberto   I2PHD
----------------------

----------------------- attached message 
----------------------------------------
Rex,
            I have been away for a few days, please excuse the delay in 
answering.
In its present implementation, what Spectran does is the following :

When you activate the 'Average' push button, a running average is computed on 
the
last five samples, BUT it is applied only to the upper part of the display, 
i.e. the
spectrum-analyser-like waveform. The waterfall is, presently, unaffected by the
computed average. This for reasons too long to be explained here. This has 
already
changed in the next beta (almost ready), where also the waterfall is subject to
averaging, which is user-selectable, from 1 (no averaging) to 100.

But the story doesn't end here. When computing spectra with high resolutions, 
you are
faced with a dilemma : if you update the waterfall only when a completely new 
set of
values are computed, then you might end up with a very slow refresh rate, one 
update
every,
let's say, 30 seconds or one minute, which not always is what is desired.
To overcome this, the technique of overlapping is used, where you apply a 
sliding window
to the data, reusing a portion of the old data together with some new ones. 
This permits
a much frequent updating of the screen. However, a side effect of this 
technique is a sort

of averaging applied to your displayed data. Spectran applies a variable 
overlapping
factor, continously measuring the CPU load, to keep the CPU near to full 
utilisation.
Hence, also the averaging effect is varying, depending on the instantaneous CPU 
burden.
In the upcoming beta, this has changed, in the sense that you can choose 
whether continue
to use this method, or set a fixed overlapping factor (which of course must be 
compatible
with the cycles your CPU can deliver to the program). Setting this factor to 1 
will
eliminate altogether whatever averaging is done on the display (and will make 
your
refresh rate slower).

Hope this answers  your question,

73,
Alberto   I2PHD
--------------------------------





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Date: Mon, 24 Apr 2000 12:53:58 +0200
From: Alberto di Bene <[email protected]>
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To: "'Geri' Kinzel, DK8KW" <[email protected]>
Subject: Re: Spectran Beta 2c
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