понедельник, 27 сентября 2010 г.

FSK: "Avaris" - domestic(Russia) system of special communication on VHF

"Avaris" - special-radio service(VHF), FM-GFSK, Br-9600.

Author: SergUA6
Band Width ~12000 Hz
Baud Rate 9600 Hz
RX mode Source I/Q record


Sonograms:

pic.1 General view


Diagrams:

pic.2 Signals demodulation

Pictures:


pic.3 General structure of the signal




"Avaris" - domestic(Russia) system of special communication. In a basis of this system, lies using of special repeaters under similar mark "Avaris". Repeaters provide expect the basic functions, also functions of recording coded/encrypted speech messages and their subsequent transfer to concrete addressees or group of users. In this system, and not only in this, speech is digitized by means of the delta modulation. The received digital stream is ciphered and transferred, in this case, GFSK modulation is used.


среда, 22 сентября 2010 г.

SA Update: RRC filter is added.

SA update to version 6.2.1.4


Three new elements are added:

1.In the module of form viewer: median filter had been replaced by new RRC filter. By default alpha = 0.5

2.RRC filter is also added in the module of FSK-2 demodulator.Alpha=0.5 by default. If RRC filter is in OFF state, then the filter, which is analogous to the main filter, works in the signal's form viewer module.

3. The following elements are added in the module of FSK-2 demodulator:

1) elements of image vertical scaling
2) an indicator of filtration process
3) the buttons of filtration start and back into initial state.
4) the cutoff range(frequency) in RRC filter can be specified from 5 Hz to Fd/2 Hz. where Hd is sampling rate. In usual(special, soft) filter cutoff range can be specified only from 30Hz to Fd/3, in the force of realization specifications.

Special attention is focused on saving of signal's fase before filtration and after filtration. The phase do not change
guaranteed.

Also some minor bugs, which had been found by users, are correct.


суббота, 18 сентября 2010 г.

MFSK: NEXEDGE

NEXEDGE
NXDN - 4800, 2400. C4FM, BW ~ 10000 Hz, 5000 Hz



Author: SergUA6
Band Width ~10000 or 5000 Hz
Baud Rate 4800 or 2400 Hz
n-Ary (PSK/MPSK) C4FM
Count of Carriers 4
ACF ~ 80, ~ 40 ms
RX mode Source IF record

Sonograms:

pic.1 General veiw NXDN with speed 4800

pic.2 Generalview NXDN with speed 2400

Diagrams:

pic.3 Manipulation speed 4800

pic.4 Manipulation speed 2400

Pictures:

pic.5 Sub-optimum demodulation 4800

pic.6 Sub-optimum demodulation 2400

pic.7 ACF NXDN in 2400 mode, only 80 ms

NEXEDGE - is the communication system using NXDN protocol. NXDN is the joint development Kenwood and ICOM companies. The protocol is declared as opened one, modulation which is used on VHF, is the classical C4FM. The Same type of modulation is also used in the other
known communication system APCO-25 on the basis of standard P-25.

On it similarity comes to an end, P-25 and NXDN are incompatible.

As a whole, the signal is easily identified, especially in SA last versions: there are special possibilities, for confident enough identification C4FM. Two variants of the signal are prepresented on the records: broadband, under the standard channel by a strip/band 12.5 kHz, and narrow-band under the channel 6.25 Khz. The maximum technical speed accordingly in a broadband mode 9600 bps, in narrow-band 4800 bps. Thus clock frequency of manipulation for C4FM turns out twice less, 4800 Hz and 2400 Hz.


среда, 15 сентября 2010 г.

SA update to version v 6.2.1.2: An output from discriminator and program processing.

SA update to version v 6.2.1.2


Two new elements are added.

The double half-wave detector, and the module of FSK-2 demodulator.

The double half-wave detector, generally, has narrow enought area of application, and as a whole, it strongly loses to the quadrature detector. However, has a high processing speed, and in some cases, it allows to solve problems of reception of clock frequency of manipulation, while other methods work very poorly or don't work absolutely.

Usually, the problems with reception of clock frequency of manipulation occur, when the record represents as not the radiosignal, but the voltage of manipulation, received after FSK, FМ or АМ detector.

Just for such cases the double-half wave detector, which solves this problem successfully had been added. In generall it concerns FSK-2, modulations C4FM and some other signals.

More important updating, is the introduction of module of FSK-2 demodulator.

Current realization is the base concept, and means further development.

Synchronization on clock frequency is carried out manually (at least currently). It isn't difficult, but demands some skills.

Exact phasing is should be done in last moment/time!

The first step: to expose/specify exact clock frequency. It should be done by zero beating, which are well visible at the corresponding scale on an axis X. Frequency is entered directly in manual from the keyboard (at it finished of input must be pressing of "Enter" key), or changes through control elements on the panel.

The second step: is the installation of rough phasing through the slider in the bottom of display window.

Last step, is adjustment of a phase for reception of as much as possible accurate clear picture.

After all these actions, a line of action/line of solution should be exposed in the necessary position (usually on the middle), if the signal is qualitative enough, and it was possible to receive a good picture of separation of levels. And it becomes possible to get the bit stream. All what is above the line of solution is considered to 1(0), all that is below the line of solution to 0(1).

I want to underline, although the module is intended for FSK-2 signals, it has much more extensive application field, as all SA tools.

In particular, with its help it is possible to realize the following tasks easily:

1 - to identify such kind of modulation as C4FM
2 - To realize a quality estimation of various signals etc.

The more detailed information about how to work with this module and practical application of new SA features is described in the article An output from discriminator and program processing.

Good Luck~

пятница, 3 сентября 2010 г.

OFDM, COFDM: CIS-59, Known as the "Ferrite", perhaps an experimental(inner) brand.

CIS-59, Known as "Ferrite", perhaps an experimental(inner) brand.
Ch-59, Br-40 Hz, Sh-50 Hz, QAM-64, k = 1/4 = 0.25




Author: SergUA6
Band Width ~3000 Hz
Low Range ~330 Hz
Baud Rate 40 Hz
n-Ary (PSK/MPSK) QAM-64
Count of Carriers 59
Step between carriers 50 Hz
ACF ~175 ms
RX mode SSB

Sonograms

pic.1 Generall view

Diagrams
pic.2 Phase constellation in the channel

pic.3 Synchronization symbols (every 7th symbol)

Pictures
pic.4 ACF

CIS-59 "Ferrite" - The name "Ferrite" quite possibly is not wide known. We can suppose it is an internal trade mark of the manufacturer. The manufacturer is unknown (at least to me), but it is known that it is domestic (Russian) development . The record has an exellent quality, all parameters are easily defined in SA.

I would like to mark some features of this signal, these are:
  1. special symbols the synchronization/adaptations (every seventh symbol).
  2. the form of constellation QAM-64 is characteristic more likely for NATO signals, than for signals CIS.

The maximum technical speed = 59 (quantity channels) *40 (clock frequency of manipulation) *6 (quantity of bits in one position QAM-64) minus synchronization symbols, that makes 14160 - (14160/7) ~ approximately 12137 bps.

The signal is generated by A model.

The detailed information about models/types of OFDM is in article/update version SA update to version 6.1.2.7 & OCG update to version 1.0.2.7


четверг, 2 сентября 2010 г.

Parameters of OFDM signals. and SA update version 6.2.0.9

Update SA to version v 6.2.0.9


Function of obtaining an exact value of the clock frequency manipulation signals OFDM is added in OFDM module.


Of course it is only within reasonable limits, we are not talking about the absolute accuracy, since all measurements are statistical in nature, and there is always some error. Just this error, in our case, is very small.

Also we updated OCG program to version 1.2.0.9


Small calculator for getting basic parameters of OFDM with CP is added.

We also created an interesting article Parameters of OFDM signals.

This article contains:
  • an interesting information about parameters of OFDM signals
  • implementation of SA new version at analysis of OFDM signals
  • examples on the real signals from the air
  • features of OFDM analysis (like "magic" coefficient "k")
  • and small lessons how to analyze OFDM signals
We are very hope you will find it interesting and usefull.