Move the specified slider and be convinced that "the good side" is really good, and that it's lengh takes precisely LG size, and that on this side all channels, which are entering into LU have stable amplitude and location.
Certainly you will notice that the real signals, behave a bit differently than an ideal ones, but you will also notice that the negative triangle does not promise anything good, and that it is useless to search for anything on "the bad side of triangle", because there simply nothing to search for. You will see, that, in general, all OFDM signals with CP submit to the common laws, considered by us that. Thus as soon as the marker leaves "the good side", FFT spectrum starts to behave strange, unpredictable etc.
Let's consider some practical nuances:
Please Pay attention, on the field LU (FFT Size) = X, where is X - os the FFY block sizeFT, or size of LU in countings. On real signals, X can be any. Actually, only the even size can be considered as the correct. Odd size of LU says that, sampling rate, or signal's shift by frequency, or all that have together led to the fact, that LU precisely lays down on odd quantity of countings of sampling rate. It is not forbidden, but it is not correct. Althogh, even in this case, the program works, as we use FFT algorithm working with any quantity of countings.
Why the yellow marker sometimes is a one pixel thick, and sometimes it is rather wide bar? Here all is very simple:
The size of LS is not limited formally, there can be signals both with LS=20 and with LS=2000, and for more comfortable observation of "the magic triangle", the map is scaled, and sometimes, there are 20-30 or more of countings in one pixel, in this case, then the marker is a thin line, and sometimes one counting is expanded on several pixels, and then the marker is wide.
You can consider the results of spacing and speed of manipulation as correct or atleast very close to real ones only, in case when:
1 - your triangle is motionless at symbol-by-symbol moving,
2 - LU is even,
3 - peak is positive
Otherwise it is necessary to speak about conditional enough accuracy.
Actually, you will notice that OFDM signals, allow rough enough inaccuracies. The very good spectra can be seen even at the big errors, moreover, it is also possible to receive the quite good constellations in the channels, but it concerns only to relative sorts of manipulation. The absolute constellations in channels, such as QAM, demand very serious measures of bringing on parametres of a signal to true ones. But this is already future...for now I suggest to be mastered with this tool SA OFDM module, this tool allows to do very many things, for example, like this:
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