Von: Alberto di Bene, INTERNET:[email protected]
An: "'Geri' Kinzel, DK8KW", DK8KW
Datum: 24.04.100 12:55
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
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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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