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SA updates from version to version
Change FSK detector to Phase detector, and add view differential PSK modes.
Начало » Руководство пользователя SA
Разместил (Author): SergUA6 6.0
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Updating of SA from version to version

The Spanish colleagues (Alipio), have suggested to substitute FSK the demodulator for the phase detector. Testing has shown extremely good results, and I have found it is possible to abandon the FSK demodulator in favour of the phase detector. Obvious minuses are not detected, on the contrary, the phase detector fulfils functions of FSK demodulator much better, it also has very high linearity and much greater processing speed, in a number of cases it gives unachievable earlier results. In principle, this is the same frequency detector, but realized through the calculation of the difference between the phases of neighboring sample signal. The order of work is remained the same, select the strip/line of the signal, that you want to process and call the phase detector. Results of detecting, as well as with the frequency detector, are researched in a viewer of signal’s form or in VMW. In general, replacement has not led to essential changes in operation with signals, except obvious improvements.

As an example, the voltage of manipulation of the signal T-240, after the phase detector and processing of LPF with frequency of a cut in 16000 Hertz is shown. The frequency detector gives, in this case, considerably worst results.

One more example, a comparison of the same signal STANAG-4528. After FSK and the phase detector in VMW, it is obvious, that the phase detector gives much more detailed picture.

The second addition in version is about the phase viewer.
It is well known that the phase manipulation can be relative and absolute, except that, there is a wide class of signals using manipulation with "rotating phase", these signals have a feature: phase has never been delayed on one/same position more then on the clock, the typical representatives of such signals are SDPSK, pi/4 DQPSK, (3*pi)/8 DPSK-8 and others.

Displaying of not absolute positions of points, but relative positions of points, makes it easy to identify the class of the signals with the “rotation phase”, and also from the theory, in this case, the viewer becomes invariant to phase of the carrier oscillation, that is, synchronization to within phase is not required, that allows in number of cases to determine the type of manipulation in questionable situations. As detailed consideration of the question of relative sorts of manipulations is beyond of the description of updates, I will be restricted to simply examples.


In absolute values of PSK-8 with forbidden transitions in relative PSK-4.


Here is more interesting result. In absolute values the constellation is totaly not clear, earlier declared PSK-9 is not very convincing, because it hides as soon as possible, but there are no doubts that some kind of relative sort of manipulation is used.

I will remind, that the difference of constellation’s phases of points is calculated and displayed, it means that the presence of clock synchronisation is necessarily. If it is turned off, then the usual pattern of trajectories of points motion is displaying.

At the displaying of relative angles in the plane, it doesn’t matter what mode(n-ary) is specified in viewer, but since it influences the general synchronization on the carrier, it is always turned on.
It is still recommended to specify this value according to absolute manipulation, or to turn on Slowly of PPL loop to avoid the slip of the frequency in the far side. It will almost automatically shutdown the self-tuning system, because in this mode, this system has not made any special efforts to keep the signal, and in the case of the strong differences it will not go into racing.

In general, synchronization by the carrier is always welcome, another thing that it can not always be provided ..

Diff can take four values:
0 - an absolute picture on a phase plane
1 - the first difference
2 - the second difference, it is used sometimes, but we didn’t find examples of that using yet
3 - the third, such sort of relative manipulation is mention in the literature, so it is entered just in case.

The Phase demodulator has not been linked yet to the values of this field, it does demodulate in usual mode, there are some unresolved nuances.

In version the more precise correction of Br is implemented and two signs after comma/point are supported. Materially, the precision of correction is limited by the precision of measurements of the clock frequency, at the worst (it is assured) the precision is +/- 0.1 Hertz, usually +/ - 0.02-0.05 and even is less.

Good luck!
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Файл создан: 13 May 2009 01:31, посл. исправление: 28 Feb 2011 00:53
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