Measurement of telegraphic distortions in a communication channel. Section III Checking and adjusting telegraph channels and equipment
^Structural diagrams for the transmission of discrete signals
1. Structural diagram of telegraph communication.
Picture. Structural diagram of telegraph communication.
The block diagram of telegraph communication consists of terminal points (OP), telegraph channels and switching stations (CS). Distinguish between switched and non-switched telegraph communications. With switched communication, UEs can be connected to each other for the duration of the message transmission. Switched communications are characterized by a permanent connection of two UEs, regardless of the presence of messages to be transmitted. The equipment includes: a direct-printing telegraph apparatus (TA) and a calling device (VP). Each OP can transmit and receive telegrams, so the telegraph machine is a transceiver. With the help of the VP, the operator-telegraph operator of the end point makes a call to the CS, establishes a connection with the desired OP and hangs up after the end of the telegram.
2. Block diagram of data transmission.
Picture. Block diagram of data transmission.
The data terminals (ODD) are interconnected by a communication channel, which is used as a standard PM (tone frequency) channel or a TT (tone telegraphy) channel. The EMA contains data processing equipment (DPE) and data transmission equipment (DTE). The OOD includes data input-output devices (IUV), the tasks of which are manual or automatic input of a message to be transmitted to the ADF; receiving a receiving message from the ADF and writing it to a medium (most often paper); undocumented display of transmitted and received data on a TV screen or scoreboard.
APD contains: RCD - error protection device, UPS - signal conversion device, UAV - automatic call device. AO - the operator's office apparatus - telegraph or telephone, depending on the type of channel used. The RCD detects and corrects errors that occur in data during transmission. The UPS converts the signals transmitted by the terminal installation into a form that ensures their transmission over the channel, i.e., it coordinates the parameters of the signal and channels; at the reception, the inverse transformation is performed. The combination of UPS receiving and transmitting is called a modem. The UAV serves to establish a connection between two DMAs, exchange service signals, and participate in official negotiations by operators who serve the DAA.
3. Block diagram of facsimile communication.
Picture. Structural diagram of facsimile communication
Fax communication is carried out via non-switched PM channels. A fax machine (FA), connected directly to the PM channel without any auxiliary devices, is a transceiver.
Questions for self-control
Explain the principle of switched and non-switched telegraph communication.
What devices are included in the data transmission equipment?
Purpose of automatic call device?
What can be the office apparatus of the operator, depending on the communication channel used?
Topic 1.3 Telegraphy methods
A method for transmitting discrete information. Single-pole and double-pole telegraphy, direct current. Tonal telegraphy with VRK. Simplex, duplex, half-duplex ways of transmitting discrete information. telegraphy speed.
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Telegraphy methods
Telegraphy methods are distinguished by the nature of the current sendings during the transmission of code combinations and by the method of correcting the transmitting and receiving devices.
Code combinations can be transmitted by parcels of direct or alternating current. When telegraphing with direct current, a distinction is made between single-pole and double-pole telegraphy. With single-pole telegraphy, current parcels are formed in only one direction, a pause between parcels is indicated by the absence of current. This method is called passive pause telegraphy. When the working message is transmitted by the current of one direction, and the pause is transmitted by the current of the other direction, telegraphy is called bipolar or active pause telegraphy.
Picture. Telegraphy: a, b - single-pole; c - bipolar.
The advantage of bipolar telegraphy is greater noise immunity and greater telegraphy range.
Each element of the code combination can be transmitted in parallel over a separate wire (the number of wires depends on the number of elements in the code combination) or sequentially over one wire.
End devices can operate in one-way, two-way serial and two-way simultaneous communication modes.
According to the method of correction of the transmitter of station A and the receiver of station B, telegraphy can be synchronous and start-stop.
Picture. Message transmission by parallel code.
For example, the five-element code combination 00101 can be generated using five keys K 1 -K 5 of station A. All keys are connected in parallel to the battery. To transmit each element of the dialed code combination to station B, it is necessary to have five lines connected to five receiving electromagnets EM 1 -EM 5 . The need to have the same number of lines as the number of bursts makes the communication system complex and expensive.
More simple option is a single line system. However, it is impossible to transmit all messages in parallel over one line, i.e. all parcels at once. Parcels must be transmitted sequentially from the first to the last (n-th). To do this, the parallel code, fixed by the spatial position of the keys, must be converted into a serial one with serial connection to the keys in the order of the parcel numbers from one to the nth. The reading of the spatial code combination and the transfer of its elements to the line occurs with the help of rotations of the transfer brush. The brush of the read element is connected in turn to the line to the first key, to the second, etc. On the opposite side, the receiving brush connects the corresponding electromagnets of the receiver to the line. The write speed in the receiver must be equal to the read speed of the transmitter. The phase of the receive brush must match the phase of the transmit brush. This method is called synchronous telegraphy. The transmission of one code combination occurs in one revolution (cycle). Readers not only read the code combination fixed in the transmitter, but also distribute the sequence of sending the code combination to the line, therefore they are called distributors.
Picture. Sending a message by serial code.
With the start-stop method of telegraphy, the distributors of transmission and reception after each cycle stop in the same position, called a stop. The receiver distributor is stopped by a stop message sent from the transmitter, the duration of which is 1.5t 0 . The beginning of the transmission of the next codeword is determined by the start message, duration t 0 . When using the MTK-2 code, one start (t 0), five informational (5t 0) and one stop (1.5t 0) elementary telegraph parcels with a total number of 7.5 t 0 are transmitted to the line.
T 0 is the duration of an elementary telegraph message.
stop
startup
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The principle of frequency telegraphy
Frequency telegraphy is a method of transmitting information by alternating current, modulated by telegraph signals.
When the working contact KR of the key K is closed (Figure a), the generator G is connected to the line. Alternating current begins to flow through the line. Alternating current pulses are called telegraph parcels. As a key K, an electromagnetic or electronic relay is used. To control the operation of the relay, elementary telegraph messages are sent to it from the output of the telegraph apparatus (Figure b). If the duration of the telegraph message is t 0, then during the same period of time the key K is closed to the working contact KR. After the time t 0 has elapsed, the key K goes to the rest contact of the KP, i.e., the connection circuit of the generator with the line opens, and the transmission of the telegraph message stops.
As a result, the code combination consisting at the output of the transmitter of the telegraph apparatus from a combination of elementary telegraph parcels direct current, is converted into the same combination of AC telegraph bursts propagating along the line. The process of controlling the duration of the AC pulse entering the line is called modulation.
Picture. The principle of frequency telegraphy using the AM method:
A) transmission to the AC line
B) parcels from the transmitter of the telegraph apparatus
C) amplitude modulated current
With amplitude modulation (AM), the amplitude line signal changes from zero to the maximum value at the moment of closing the key and from the maximum value to zero at the moment of its opening. Fluctuations in the current flowing into the line is called the carrier. Their frequency and amplitude remain constant during the time t 0. Frequency modulation (FM) consists in the fact that during the action of the current telegraph message, a generator G 1 is connected to the line, generating oscillations with a frequency f 1. During a currentless message from G 2, oscillations with a frequency f 2 enter the line. The amplitude of the oscillations remains constant. With phase modulation (PM), at the moment of changing the polarity of the package, the phase of the alternating current changes. The current amplitude during FM remains constant.
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The principle of voice-frequency telegraphy in FDC
Picture. Scheme for simultaneous transmission of two messages.
Tonal telegraphy is more common, since the tonal frequencies correspond to the spectrum of a standard PM telegraph channel, through which, thanks to FDM, up to several dozen messages can be transmitted.
Consider a scheme for the simultaneous transmission of two messages. One telegraph message is transmitted from telegraph machine Tper1, the second message - from Tper2. Elementary telegraph messages from the transmitter Tper1 are fed to the modulator M1, to which the generator of carrier oscillations G1 is connected, with a frequency F1. Modulator M2 receives elementary telegraph messages with Tper2 and carrier frequency F2 from generator G2.
When M1 receives a positive current elementary telegraph message from G1, carrier F1 will appear, reduced by f. The currentless message corresponds to the carrier frequency F1 increased by f. Therefore, at the output of M1 there will be a frequency band F1±f, respectively, at the output of M2 - F2±f. The value f is called frequency deviation (possible frequency deviation).
From the output M1, the signal enters the bandpass filter PFper1, which passes the band F1±f into the line, PFper2 passes the band F2±f. On the receiving side, the telegraph signals pass through the PFpr1 and enter the amplifier, which compensates for the loss of signal energy due to attenuation in the line.
In the demodulator DM1, the AC pulse is converted into an elementary DC telegraph message, which drives Tpr1.
The set of elements (M1, PF1, U1, DM1) through which the message passes from the TA transmitter to the TA receiver is called a telegraph channel.
In order to transmit telegraph messages over a communication channel without distortion, telegraph channels must have a bandwidth equal to the width of the spectrum of the transmitted waveform. The value of F1+f is called the upper characteristic frequency. The value of F1-f is the lower characteristic frequency. The bandwidth F = 2f depends on the telegraphy speed.
F1(1.4 1.8)v
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The principle of time division of channels (TSC)
Picture. Structural diagram of a line with a VRC.
TRC is a method of simultaneous transmission of several telegraph messages over one communication line or in a PM channel, in which the line or channel is occupied in turn by each message at regular intervals.
Consider the WRC method using the overlay method. Code combinations from the output of the telegraph transmitter (Tper1 and Tper2) are fed to the electronic transmission distributor (Pper). Figures a and b show the code combinations at the output of each of the devices. A pulse carrier is supplied to the transmission distributor from a pulse generator (Fig. c). Let us assume that the rhythm of the distributor operation is such that it passes odd pulse carriers (marked with a dot) when the current elementary message from Tper1 acts at its input, and even ones when the current elementary message Tper2 acts. As a result, a pulse sequence will enter the channel (Figure d). The receiving distributor Rpr, working synchronously with the transmitter, will send odd pulses (Fig. e) of the carriers to the receiver Tpr1, and even pulses (Fig. e) to Tpr2. After demodulation, i.e., converting the sequence of pulses of a current or currentless message (Fig. g, h), they are fed to the corresponding receivers Tpr1 and Tpr2.
To synchronize the reception distributor with the transmitting side, clock pulses are sent that are associated with the frequency of the pulse carrier and are generated by a clock shaper (FSI). On the receiving side, the clock pulses are selected from the common sequence by a clock pulse selector (FSI), and the pulse generator G2 is controlled, which generates a sequence of pulses with a frequency equal to the carrier pulse repetition frequency.
Thus, two telegraph messages are transmitted simultaneously over one PM channel, i.e. the PM channel is sealed with two telegraph channels.
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telegraphy speed
Each telegraph message is transmitted at a certain speed. The speed of telegraphy is measured by the number of elementary telegraphic parcels transmitted in one second. The unit of speed is baud. If 50 elementary packets are transmitted in one second, then the telegraphy rate is 50 baud. The duration of one elementary parcel in this case is equal to:
V \u003d 50 Baud t 0 \u003d 1 / 50 \u003d 0.02 s. = 20 ms;
V \u003d 100 Baud t 0 \u003d 1 / 100 \u003d 0.01s \u003d 10 ms.
Therefore, the speed of telegraphy is related to the duration of the elementary parcel by the relation:
V = 1 / t0; t 0 \u003d 1 / V
The shorter the duration of an elementary telegraphic message, the greater the speed of telegraphy.
All permitted transmission speeds:
low - 50, 100, 200 baud;
medium 660, 1200, 2400, 4800, 9600 baud;
high - more than 9600 baud.
The speed of telegraphy depends on the type of telegraph machine. For direct-printing telegraph devices, the telegraphy speed is determined by the formula:
V = (N K) / 60,
Where N is the number of characters transmitted by the device per minute;
K is the number of elementary telegraphic parcels required to transmit one character.
Most start-stop telegraph machines allow you to transmit 400 characters per minute, and one character is transmitted by 7.5 elementary telegraph parcels. Therefore, the speed of telegraphy is:
V = (400 7.5) / 60 = 50 baud.
The data transfer rate (information rate) is measured by the number of information units per second and is determined by the formula:
B \u003d (N K`) / 60,
Where K` is the number of information units to transmit each character.
For example, B \u003d (400 5) / 60 \u003d 33.3 bps, because when using the five-element MTK-2 code, only five information elements carry information about the sign.
Questions for self-control
List the methods of telegraphy according to the nature of the current sending when transmitting code combinations.
What is the difference between synchronous and start-stop telegraphy?
Explain the tone telegraphy method.
Explain the principle of telegraphy in PRK.
Explain the principle of telegraphy in VRK.
The concept of telegraphy speed. Units.
Topic 1.4 Encoding Messages
Simple and redundant codes. Codes MTK-2, MTK-5, KOI-7, KOI-8, SKPD. Matrix and cyclic coding.
Message Encoding Principle
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Telegraph codes
When transmitting a message by telegraph communication, each sign of the message is converted into a combination of current and current-free parcels or current parcels in different directions. Such a combination is called a code combination. The process of replacing the transmitted character with the corresponding code combinations is called encoding. The table of correspondence of code combinations to transmitted characters is called a code.
All discrete messages are converted into an electrical signal using certain codes. These codes are called primary. Then, to increase the noise immunity, secondary redundant codes are used, which are formed using the primary ones, i.e. a certain block is compiled from combinations of the primary, check bits are determined using mathematical transformations, and then a block of redundant secondary code is formed from check and information ones.
Morse code was the first standardized electrical telegraph code - signs were transmitted using parcels. electric current different duration - dots and dashes. The shortest message - a point, duration t 0 , from which all code combinations are composed, is called an elementary telegraph message. The duration of the dash is equal to the duration of three elementary telegraphic messages 3 t 0 . This code is uneven, since an unequal number of elementary parcels is needed to transmit different characters.
A uniform code is characterized by the fact that a combination of an equal number of elementary telegraphic parcels is used to transmit any character. Any of the uniform codes, the combination of which is formed from two values of the parcels: current and currentless, or the current of one direction and the current of the other direction, are called binary or binary. The number of current values that the elementary package acquires during transmission is called the code base. The possible number of code combinations A for a uniform n-element binary code is determined by the expression:
where m is the base of the code.
The five-element code gives 2 5 =32 code combinations, and the seven-element code 2 7 =128 code combinations.
The Baudot code is five-element, i.e. any code combination consists of five elementary parcels.
When using a five-element code, 32 code combinations are not enough to transmit a telegraph message. The number of code combinations can be increased in two ways: by increasing the number of elements in a code combination, or by introducing registers. In this case, the required number of characters is divided into registers (two or one): Russian, Latin, digital. In this case, different characters are in different registers, they are transmitted by the same code combination, but before its transmission, a signal is given corresponding to the register in which the transmitted character is located. The disadvantage of register codes is the reduction in the availability of message transmission, i.e. execution of one register combination causes incorrect decoding of the code combination following it. With the introduction of multi-element codes, the duration of combinations increases, hence the number of messages transmitted per unit of time decreases.
The international code MTK-2 is five-element, three-register. The current message is designated 1, the currentless message is 0. For example, the sign (symbol) A will be written with the MTK-2 code - 11000, and the symbol H - 01010.
MTK-5 - seven-element, two-register.
In codes for the exchange of information in data processing systems, groups of control and graphic characters are provided. The group of graphic characters includes numbers, uppercase and lowercase letters, and special characters. Of the entire set of symbols, GOST establishes five sets of H0-H4. All sets include control characters, numbers, and special characters. The H 0 set includes uppercase and lowercase Latin letters. Set H 1 contains only Russian letters. All installed characters include H3. Set H 4 contains only numbers, special characters and control characters.
The code KOI - 7 has three sets: KOI - 7Н 1 , KOI -7Н 0 , KOI - 7С 1 - code of additional service characters.
The structure of codes of the full set H 0 , H 1 is a matrix of eight columns and sixteen rows. Each of the 128 code combinations of the matrix, due to the numbering of columns from 0 to 7 and rows from 0 to 15, is designated by the name of the set and a fractional number: the numerator is the column number, the denominator is the row number. For example, H 0 4/5 corresponds to the Latin letter "E". Except fractional number any symbol of the table is given in the form of a code combination, denoted b 7 b 6 b 5 b 4 b 3 b 2 b 1 , in which the index bit indicates the ordinal number of the code combination bit. The three most significant bits (b 7 b 6 b 5) are shown above the serial number of the column of the code table, and the remaining four (b 4 b 3 b 2 b 1) are at the level of the serial number of the line. With serial transmission to the line, the combination comes from the least significant bit.
The standard SKPD data transmission code is eight-element, two-register. In addition to the seven information bits, the combination includes the eighth bit, which is a service bit. The value of the eighth digit is chosen so that the total number of units in the code combination is even. This provides the simplest defense from mistakes.
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Redundant coding
In modern data transmission equipment, two methods of redundant coding are most often used: matrix and cyclic. Both methods are based on the coding of individual information blocks of a sufficiently large length, therefore these codes are called block codes. The composition of the complete block transmitted over the channel includes m*q information bits and r check bits. The latter are formed by arithmetic operations over the original information bits.
In matrix coding, modulo 2 addition is used. The initial binary numbers of the code combination are written as a mathematical matrix. For example, five combinations of the five-element code m=5,Q=5=>m*Q=25 must be transmitted with error protection. We write these combinations in the form of a matrix, placing the digits of the same name one under the other.
1st QC 01011 0+1+0+1+1=1
2nd QC 10001 1+0+0+0+1=0
3rd QC 11101 1+1+1+0+1=0
4th QC 00111 0+0+1+1+1=1
5th QC 10010 1+0+0+1+0=0
We perform modulo 2 addition of all rows and all columns. As a result of addition, we get two check numbers - the sum of the rows and the sum of the columns. Those. the complete block of the matrix code will consist of seven five-element combinations: five informational and two verification.
The test combinations are usually transmitted over the channel at the end of the block. In the receiving equipment for data transmission, the RCD checks the unit for error-freeness. Why six rows and six columns of the complete block, including check bits, are summed modulo 2. Zero results of all additions indicate that there are no errors in the received block. The presence of 1 in the right column or bottom row is a sign of an error in the block.
Another class of redundant codes are cyclic codes. Unlike matrix codes, cyclic coding The basic mathematical operation is the division of binary numbers. Divisible is a binary number - the original code combination KK. The divisor is a binary number common to the entire code as a whole. This number is called generator. The number of digits and the composition of the generating number determine the protective properties of the code, i.e. error rate. The result of dividing the original combination by a generating number will be some quotient and a remainder. The remainder is included in the full block as check bits. That is, the cyclic code block will consist of a dividend (information bits) and a remainder (check bits). The quotient obtained by division is not used.
The detection and correction of errors in the cyclic code is based on the following arithmetic position: if a remainder is added to the dividend and the resulting number is again divided by the same divisor, then the division will occur without a remainder. To check the code combination, the receiving error protection device divides this combination by the same generating number as when encoding. If there are no errors, the division will result in a 0 remainder. If the remainder differs from 0, this is a sign of an error, the combination is erased and re-requested.
For example: the length of the initial information combination is 11 bits, the number of check bits is r = 4; the generating number of the cyclic code has the value 10011.
The encoding of the original combination includes the following operations:
1) the original combination is represented as a binary code.
The number is multiplied by a factor like 10000, where the number of zero digits to the right of 1 is r.
11010010001*10000=110100100010000
2) The resulting product, which has 15 digits, is divided by the generating number 10011
110100100010000 10011
10011
1100011010
The remainder of the division in the form of a four-digit number will be the check bits. If the remainder has less than four digits, it must be padded with the number of zeros on the left.
3) From 11 information bits and 4 bits of the remainder, a complete combination of the cyclic code is formed.
In the receiving RCD, when checking the full combination of the cyclic code for error-free, the combination of 15 bits is divided by the same generating number 10011. After dividing and obtaining a zero remainder, the first 11 bits are displayed to the consumer of information as error-free.
Questions for self-control
What is called coding, telegraphic code?
Explain what is the main difference between simple codes and redundant ones?
How can I increase the number of code combinations?
Give a description of the simple codes MTK-2, KOI-7, KOI-8, SKPD.
6. Explain the principle of the formation of complete code combinations of a cyclic code
Control task
1. Using simple codes provide code combinations of your last name.
Topic 1.5 Distortion of discrete signals
Registration methods. Corrective ability. Types of edge distortions. Crushing.
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Characteristics of Discrete Messages
To assess purely informational transmission capabilities, a characteristic is introduced, called bandwidth - the number of information unit elements (bits) transmitted per second, depending on how many service elements have to be transmitted along with information, i.e. the presence of errors in the received information.
The characteristic of fidelity is the probability of errors:
R osh \u003d n osh / n lane.
Р osh - the number of errors,
N lane - the total number of transferred elements.
In real operating conditions, fidelity is expressed by the error rate for elements or combinations, i.e. error probability for a finite time interval. When transmitting telegram messages, it is recommended that the error rate for currents K osh< = 3 * 10-5, т.е. не более 3 ошибок на 100000 переданных трактов. При передаче данных К ош <= 10 -6
Transmitter edge distortion - the normalized value of the distortion of the transmitted elements, measured directly at the output of the telegraph transmitter. Edge distortion is measured in % of the duration of a single interval t 0 . The norm for transmitter distortion is 2-4%.
Correcting ability - characterizes the quality of the terminal receivers, their ability to withstand the effects of distortion of binary signals. Distinguish the correcting ability for edge distortion and crushing. Numerically correcting ability is expressed by the maximum value of edge distortion or the maximum duration of splitting, in which the received elements of the combinations will be registered by the receiver without errors.
cr = 8 max add
dr \u003d t dr max add
Modern receivers have a correction capability of 25-50% of the duration t 0 .
margin of stability – the difference between the value of the corrective power of the receiver and the value of the total edge distortion at the input of this receiver
= total
Therefore, for the error-free reception of the elements of the combination, the stability margin must be positive.
Reliability – characterizes the ability of the equipment to transmit information with a given value, volume and period. Failure to meet one or more of these requirements is a waiver. Rejections can be partial or complete.
Complete failure - the inability to transmit, because. equipment or channel is out of order. Maintaining performance with a partial deterioration in performance is called a partial failure.
To assess and normalize reliability, the following characteristics are used:
failure rate of elements or system - average number of failures per hour;
mean time between failures T 0 - average time of normal operation between two interchangeable failures; T 0 \u003d 1 / , then you can determine:
,where T is the uptime between two interchangeable failures.
N is the total number of failures for the observation period.
Availability factor.
Kg \u003d (To / (To + Totk))
Totk - the average duration of failure, depending on the qualifications of the maintenance personnel and the maintainability of the equipment.
All listed characteristics are averaged.
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Distortion of discrete signals
Any change in the received telegraph signal relative to the transmitted one is called distortion. These distortions can lead to erroneous reception of individual characters of the transmitted text, which leads to a distortion of the transmitted information. The cause of distortion of the telegraph signal may be various kinds of interference or unsatisfactory characteristics of communication channels.
Meaningful Moments
T0
t0
t0
t1
t1
0 1
Meaningful intervals
Picture. Edge distortion
The reliability of telegraph communication depends on the degree of distortion of telegraphic messages. Distortion - the degree of inconsistency of the received message with the transmitted one, i.e. a change in the duration or form of received parcels compared to those transmitted. Distortions of telegraph parcels are edge and in the form of crushing.
Edge distortion is a displacement of a significant moment by a different amount relative to the corresponding ideally significant moment. The significant moments of sending are the moments of transition from one value (1) to another (0), and the interval between two significant moments is called the meaningful interval. Thus, edge distortions are expressed as a change in the duration of a meaningful interval compared to the duration of the ideal value of the interval. Edge distortion - a shift by a different amount of the beginning or end (or at the same time the beginning or end) of the received elementary telegraphic message compared to the transmitted one.
Figure a shows the parcels at the output of the transmitter of the telegraph apparatus. In the absence of distortion, the parcels will be reproduced by a receiving telegraph relay or an electromagnet through t 1. The delay of parcels by time t 1 (positive individual edge distortion) causes the same shift of their boundaries (significant moments). The duration of the received messages remains equal to the duration of the transmitted ones (Figure b). Figure c shows distorted messages. Distortions consist in the displacement of the beginnings and ends of the parcels by different values tн and tк. The beginning of the parcels shifted by tn, and the end - by tk. Parcel distortions are measured as a percentage and are determined by the formula:
Edge distortions are divided into three types: predominance, random and characteristic.
Predominances are called distortions, expressed in a constant change in the duration of the message.
Random - due to the action of random interference on the duration of the message, which, under the influence of the interference current, either shorten or lengthen.
Characteristic - characterize the distortion of the signal, depending on the combination of parcels, i.e. characterize parcels that have arisen only when a short parcel is preceded by a long one or vice versa. Characteristic distortion will be the greater, the greater the difference in the duration of the received parcels.
Parcel distortion is determined by all types of edge distortion simultaneously, so the total distortion is equal to:
total = pr + char + sl.
Crushing - such distortions of the parcels, when there is a change in the polarity of the parcel for its part or for the entire duration.
The reason for fragmentation is the most intense interference of an impulse nature, as well as short-term breaks. The appearance of crushing is random. Splitting has a sign that determines the direction of change of significant position. The duration of crushing is a random variable that varies within 0
=
,
Where n dr is the total number of fragmentations recorded during the measurement Tism. The value of is the probability that any arbitrarily chosen element of the CC will be hit by crushing.
Groups of splits that have one common cause are called batches of splits.
Edge distortion and fragmentation are the causes of errors in the received information. Error - incorrect determination of the significant position of the received QC element. Such an error is called an elemental error. Depending on the number of elements received incorrectly, single, double, etc. are distinguished. errors. The most unfavorable for recognition is a double compensation error, called the bias error - the simultaneous transition of 1 to 0 and 0 to 1 within the QC. For example:
Transferred 10110 00101 10101 00100
Accepted 10010 01001 11011 10111
Errors 00100 01100 01110 10011
Errors can occur:
1) through the fault of the operator conducting the transmission or preparing the message for transmission;
2) due to errors and words in the transmitter and receiver;
3) due to interference of various kinds in communication channels.
Interference is called extraneous voltages that randomly arise in the channel and enter the receiver input together with the transmitted signals.
Questions for self-control
Characteristics of discrete messages.
List the causes of distortion.
What distortions are called edge?
Explain the concept of meaningful moment, meaningful interval.
List the types of edge distortions.
What is the degree of admissible edge distortion with the corrective ability of the telegraph apparatus 25%.
What distortion is called crushing?
What are the possible reasons for errors?
Control task
1. Draw a timing diagram of the start-stop combination of the letter given in the table without distortion and with distortion for single-pole telegraphy at a given telegraphy speed.
2. Determine the degree of synchronous distortion.
3. Explain how the offset of the start-stop transition affects the moments of registration.
4. Determine the amount of allowable edge distortion when the start-stop transition is shifted towards the delay by t lane
| Number Option |
Discrete signals transmitted over circuits and communication channels are subject to distortion and various types of interference, as a result of which the received pulses may differ from those transmitted in shape, duration and polarity.
It is not difficult to restore the shape of the received impulse using, for example, a relay, a trigger, and similar elements. However, the process of restoring the shape may be accompanied by an additional change in the duration of the received pulse, since these elements have a finite sensitivity (threshold).
With the correct response threshold ln of the relay element, the pulses are recorded without distortion and only shift relative to those transmitted for a while (Fig. 37a). The shift of the response threshold leads to a change in the duration of the registered pulse. An increase in the threshold entails a shortening of the current pulses (Fig. 37b), and a decrease in the threshold leads to their lengthening (Fig. 37c).
A change in the duration of the received pulses is commonly called edge distortion, which manifests itself in the lengthening or shortening of a given pulse due to the corresponding shortening or lengthening of neighboring parcels.
The shortening of the message can reach such a value (shaded part) at which it will not be recorded by the recording element, and instead of, for example, current and subsequent currentless messages with a duration of each td, one current message with a duration of 2td will be recorded. Thus, an error may occur when receiving a pulse, which is called a pulse error. The latter can lead to a sign error, when another character is registered instead of the transmitted combination of one character of the message (for example, in the figure, instead of the combination IOII, IIII is fixed).
The occurrence of an error is also possible in another way (Fig. 38), for example, when a strong interference of sufficient duration and opposite polarity is applied to the sending. Distortions, called fragmentation distortions, occur if the duration of such interference tdr< Thus, errors in reception and distortion of pulses are due to different manifestations of the same interfering causes present in the channel. During operation, the main parameters to be controlled are reliability and edge distortion. Reliability is quantified through error rates for single elements and alphabetic characters. It is a generalized parameter that characterizes the quality of the transmitted information. Permissible error rates are set depending on the transmission rate. Indirectly, the reliability is determined by edge distortions. Although there is no one-to-one correspondence between edge distortions and an error (incorrectly received symbol), however, it can be argued with a high degree of probability that errors will appear at values of edge distortions that exceed the permissible norm. According to their properties, edge distortions are usually divided into three groups: predominance distortions (n), characteristic (x) and random (c) distortions. This does not take into account the distortions introduced by the transmitting and receiving devices of the terminal equipment. A feature of predominance distortions is the constancy in time of their magnitude and sign. They are eliminated with the help of appropriate adjustments of the receiving device when setting up the channel. A feature of the characteristic distortions is the dependence of their magnitude on the nature of the transmitted pulse sequence. These distortions are determined by transient processes in communication channels and circuits. The magnitude of random distortions, usually caused by interference, is random and varies over time according to various laws. At the same time, it should be noted that in the strict sense, characteristic distortions of predominance also arise by chance. However, they can always be eliminated with appropriate adjustments. In a discrete channel, the relative degree of intrinsic isochronous (synchronous) and start-stop distortions is normalized. Depending on the number of simple channels at the nominal bit rate, distortion should not exceed the values given in Table 6. For switched channels, one should be guided by the allowable rate for one simple channel, and for non-switched channels, the rate for seven simple channels. Table 6 Number of simple channels Permissible relative degree of edge distortion Isochronous (synchronous) start-stop When transmitting discrete signals at speeds of 200, 600, 1200 baud over PM channels, relative individual distortions should not exceed 20, 30, 35%, respectively, for switched and non-switched channels. Distortions introduced by switching device devices should not exceed 2%, and by a telegraph transmitter during manual and automatic operation - 5% when setting up the device and 8% during operation. The device ETI-69 is intended for measurement of distortions of telegraph parcels, testing of telegraph channels, equipment and relays. Technical characteristics of ETI-69: The device provides measurement of distortions of telegraph parcels in start-stop mode at fixed speeds of 50, 75, 100, 150, 203 baud. The device provides measurement of distortions of telegraph parcels in start-stop mode with smooth speed adjustment. Deviation of nominal speeds in start-stop mode does not exceed ±0.2% at normal temperature, ±0.5% at extreme operating temperatures. The device uses a discrete method of counting the measured value of edge distortions through 2% within the entire elementary package at all speeds and after 1% - within half of the elementary package. The reading of the distortion value is made by the displayed figures from 0 to ± 25% with the possibility of increasing the division value and the measurement limit by 2 times. The input device of the device is symmetrical and provides the possibility of parallel and serial connection to the measured circuit with the following gradations of input resistance: 25, 10, 3, 1 and 0.1 k0m. The input device is designed for the use of linear voltages in the tested circuits up to 130 V in single-pole mode and up to ±80 V - in two-pole mode. The test signal sensor of the instrument generates the following types of signals: The error of the bipolar messages issued by the device does not exceed 1%. The sensor outputs 120±30 V single-pole and ±60±15 V two-pole bursts at a load current of 0 to 50 mA, as well as 20+6-8 V single-pole and two-pole bursts at a load current of 0 to 25 mA. The output impedance of the device is not more than 200 Ohm. The sensor of the device also works in the interrupter mode when connected to the output terminals of the load device with an external source of linear voltage up to 130 V. The device provides the possibility of introducing distortions into the signals of its own sensor up to 95%, as well as an extraneous sensor within the limits of up to 92% - in steps of 10 and 1%. The introduced distortions are distortions of the predominance type with manual setting of any of their sign, as well as with automatic change of the predominance sign up to ±89% within the duration of the start-stop cycle up to ±50%. The device provides a performance check in the "ON YOURSELF" mode. The device with a relay test unit allows you to check and adjust the neutrality, recoil and bounce of telegraph relays of the RP-3 type. Checking the neutrality and return of the relay is carried out by rectangular parcels in the operating, test and dynamic modes. The device is powered from AC mains 127+13-25 V or 220+22-44V, 50 Hz. The overall dimensions of the device are 220x335x420 mm. Weight no more than 21 kg. The operating temperature range of the device is from -10 to +50°С. You can buy a device from storage ETI-69 (for measuring distortion of telegraph parcels, testing telegraph channels, equipment and relays) at the factory price by placing an on-line order on the website, or by contacting the company's managers. Delivery across all regions of Russia and to the Republic of Kazakhstan. Class 21a 7o5 Signature group M 86 A. B. Pugach, K. A. Brusilovsky, N. A. Berkman, V. S. Bleikhman, and S. Yu. Zlkind DEVICE FOR MEASURING TELEGRAPH DISTORTIONS Declared on June 3, 196, for Xe 733226 / 26-9 to the Committee for Inventions and Discoveries under the Council of Ministers of the USSR Known devices for measuring the distortion of telegraph parcels in synchronous and start-stop modes, made on semiconductor devices and ferrites with PPG and including a distributor on two parallel shift registers. The measurement accuracy of such devices is low. To improve the measurement accuracy, ensure the convenience of reading the distortion value and the independence of the reading from the subjective error of the observer, a device is proposed in which a matrix circuit of a start-stop discrete indicator on neon lamps is used. To ensure a certain duration of reliable ignition and extinguishing of neon lamps, as well as to increase the duration of their burning, the device uses a single vibrator on transistors, a commutator, and an accumulator of M cells. The skeletal diagram of the start-stop-synchronous discrete action distortion meter is shown in the drawing. The device contains a clock pulse generator 1, an input device 2, a memory device 3, a distributor for M outputs, made in the form of two parallel shift registers. 11, indicator 12, shift register 18 and switch 14. The specified nodes of the distortion meter are made on semiconductors and ferrites with a rectangular hysteresis loop. The indicator is made on neon lamps. The reading of distortions on the indicator is carried out by the burning of neon lamps arranged in the form of a matrix consisting of M vertical tires, the scale division is 100 lyv In the synchronous mode of operation, one horizontal matrix is used. In the start-stop mode of operation, it is possible to measure the distortion of each elementary parcel. To do this, the matrix contains six horizontals, each of which corresponds to the serial number of the studied parcels of the start-stop combination. The investigated telegraph parcels are received at the input device 2, which converts the incoming rectangular signals into a sequence of short pulses corresponding to the characteristic recovery moments (CMR) of the incoming messages, synchronized with the clock pulses of the generator 1. Each CMW following the start transition is recorded in the memory device 8. When the pulse coming from the output of device 8 and the distributor pulse (registers 4 and 5) coincide in time, a signal occurs that is fed to the corresponding element of the drive 10 through the key device 7. Thus, the HMW is fixed in the drive 10 depending on its offset from the ideal position. The number of accumulator elements corresponds to the scale division value of the device. After the HMB offset is fixed in one of the elements of the drive 10, the storage device 8 returns to its original state. After some time, the coincidence circuit 8 is triggered. The amplifier 9 reads information from the drive 10 into the forming circuit 11 and advances the information in the register 18. The forming circuit 11 contains X single vibrators on two semiconductor triodes. Each single vibrator controls a high-voltage semiconductor triode that controls the ignition of the neon indicator lamp. This ensures reliable ignition and extinguishing of the neon lamp. When measuring in the start-stop mode, the start-up of the distributor (registers 4 and 5) is carried out by the start-stop trigger 15 at the moment the stop-start transition arrives at the input device 2. The stop of the distributor occurs after the passage of six and a half elementary parcels. Register 18 containing seven elements is used to determine the moment of stopping. The same register is used to control the switch 14, which is used to switch the horizontal rows of the indicator matrix. Since the coincidence circuit 8 and amplifier 9 operate in the middle of the incoming packets of the star pattern, the switching of the horizontal rows of the indicator matrix occurs in the middle of the elementary packets. This allows you to separate the measurement process and the display process in time. Neon lamps burn the same time regardless of the amount of distortion. The described device provides measurement of distortions of telegraph parcels at telegraphy speeds up to 1000 baud with a measurement error of up to 2%. The device can be widely used at telegraph stations and in laboratory conditions. Subject of invention 1, A device for measuring the distortion of telegraph parcels in synchronous and start-stop modes, made on semiconductor devices and ferrites with PPG, including a distributor on two parallel shift registers, characterized in that, for the purpose ¹) 47/97 to improve the accuracy of measurement, ensure the convenience of reading the magnitude of distortions and the independence of the reading from the subjective error of the observer, it uses a matrix circuit of a start-stop discrete indicator on neon lamps, consisting of M vertical ones! 100 - - - - /o - the price of division of the scale and six horizontal tires, at the intersection of which ON (EN 11 INDICATOR LAMPS, EACH OF WHICH. Corresponds to a certain amount of distortion of the premise of the code combination. 2. The device according to and, 1, characterized in that, in order to ensure a certain duration of reliable ignition and extinguishing of neon lamps, as well as to increase the duration of their burning, a single vibrator on transistors is used in it, supplying control pulses to the vertical buses of the matrix, the switch and the drive of M cells. switching six horizontal tires of the matrix and synchronizing the moments of their switching with the corresponding midpoints of elementary parcels. Compiled by G. E. Emelyanov Editor N. S. Kutafina Tekhred A. A. Kamyshnikova Proofreader V. Andrianova Signed to oven, 7 VI-62 Format paper. 70; 108 l g Volume 0.26 pzg l. Zach. 6023 Circulation 800 Price 4 kop. CBTI of the Committee for Inventions and Discoveries under the Council of Ministers of the USSR Moscow, Center, M. Cherkassky lane, 2/6 Printing house CBTI, Moscow, Petrovka, 14 During operation, visual control of optical signaling is carried out, as well as periodic measurement of voltages, currents and levels at control points. For a more complete adjustment of telegraph channels and equipment with the determination of the amount of distortion, TG signal distortion meters are used, for example, ETI-69, ETI-64, IK-ZU-1, IK-1U. These devices include a test signal sensor, an IKI edge distortion meter. 3.3. Tactical and technical characteristics of ETI-69 Purpose: The device ETI-69 is intended for measurement of distortions of telegraph parcels, testing of telegraph channels, equipment and relays. The device provides measurement of distortions of telegraph parcels in start-stop mode at fixed speeds of 50, 75, 100, 150, 203 baud. The device provides measurement of distortions of telegraph parcels in start-stop mode with smooth speed adjustment. The device allows you to measure the distortion of telegraph messages in synchronous mode, as well as in the mode of measuring duration in a smooth range of speeds from 44 to 112 Baud and with the possibility of smooth adjustment of speeds of 150, 200, 300 Baud in the range from +12 to -12%. Deviation of nominal speeds in start-stop mode does not exceed ±0.2% at normal temperature, ±0.5% at extreme operating temperatures. The device uses a discrete method of counting the measured value of edge distortions through 2% within the entire elementary package at all speeds and after 1% - within half of the elementary package. The reading of the distortion value is made by the displayed figures from 0 to ± 25% with the possibility of increasing the division value and the measurement limit by 2 times. The error of the measuring part when measuring distortions from its own sensor at speeds up to 200 Baud when counting through 2% does not exceed ±2%, when counting through 1% - ±1%; at speeds of 200 and 300 baud, this error is ± 3% when reading through 2% and ± 2% when reading through 1%. The operational error of the device in synchronous mode when receiving from a sensor of another device during a measurement session corresponding to the transmission of 1000 elementary parcels at a telegraphy speed of 50 baud does not exceed ±3% with a countdown of 2%, and with a countdown of 1% - ±2%. The device registers the value of total or start-stop distortions or their maximum value for a measurement session. The device provides measurement of distortions of the fronts of each of the parcels of the start-stop cycle. The device allows you to divide the distortion into random, characteristic and predominance with the definition of their sign. The input device of the device provides reception at speeds up to 100 Baud of rectangular and rounded packages in single-pole mode and reception of two-pole packages at all speeds. The minimum current of the input device in two-pole mode is 2 mA, in single-pole mode 5 mA. The input device of the device is symmetrical and provides the possibility of parallel and serial connection to the measured circuit with the following gradations of input resistance: 25, 10, 3, 1 and 0.1 k0m. The input device is designed for the use of linear voltages in the tested circuits up to 130 V in single-pole mode and up to ±80 V - in two-pole mode. The test signal sensor of the device generates the following types of signals: Pressing "+"; Pressing "-"; - "1:1" (dots); The text "RY" according to the international code No. 2, as well as the combination of "P" and "Y" separately; Automatic alternating combinations "5:1" The error of the bipolar messages issued by the device does not exceed 1%. The sensor outputs 120±30 V single-pole and ±60±15 V two-pole bursts at a load current of 0 to 50 mA, as well as 20+6-8 V single-pole and two-pole bursts at a load current of 0 to 25 mA. The output impedance of the device is not more than 200 Ohm. The sensor of the device also works in the interrupter mode when connected to the output terminals of the load device with an external source of linear voltage up to 130 V. The sensor of the device has overload protection, short circuit alarm and protection against polarity reversal of linear power supplies. The device provides the possibility of introducing distortions into the signals of its own sensor up to 95%, as well as an extraneous sensor within the limits of up to 92% - in steps of 10 and 1%. The introduced distortions are distortions of the predominance type with manual setting of any of their sign, as well as with automatic change of the predominance sign up to ±89% within the duration of the start-stop cycle up to ±50%. The device provides a performance check in the "ON YOURSELF" mode. The device with a relay test unit allows you to check and adjust the neutrality, recoil and bounce of telegraph relays of the RP-3 type Checking the neutrality and return of the relay is carried out by rectangular parcels in the operating, test and dynamic modes. The device is powered from AC mains 127+13-25 V or 220+22-44V, 50 Hz. The power consumed by the device at the rated mains voltage does not exceed 100 VA. Overall dimensions of the device 220X335X420 mm. Weight no more than 21 kg. Overall dimensions of the BIR block 225X130X125 mm. Weight 1.6 kg. The operating temperature range of the device is from -10 to +50°С. Product composition The composition of the product includes: Device ETI-69; Relay test unit; Connecting cords; Spare parts; ETI-69 device case; Operational documentation Stacking box. Scheme of switching on the ETI device during various measurements 3.4. Methodology for measuring distortion in telegraph channels The measurement is carried out in a four-wire two-pole mode of telegraph outputs at a linear voltage of 20V, an input resistance of 1 kOhm, a CHANNEL mode. The device's distorter in the channel mode is included in the receiving part, its regulator must be set to position 0. The measuring device is connected to the switching jacks, to which the inputs (outputs) of telegraph channels are connected. Terminal telegraph equipment is switched off. From the sensor of the distortion meter, a signal of pressing “+”, then “-” is fed into the telegraph channel. When changing the polarity of the currents, it is necessary to make sure that the needle of the millimeter of the distortion meter deviates in the corresponding direction and approximately by the same amount. Having received from the opposite station pressing "+" and "-" and thus making sure that there is a telegraph channel, you should adjust the telegraph channel to a minimum of predominance. To do this, set the switches of the distortion meter to the position CHANNEL 1:1, the nominal speed for this channel, DURATION, without memorization.
The device allows you to measure the distortion of telegraph messages in synchronous mode, as well as in the mode of measuring duration in a smooth range of speeds from 44 to 112 Baud and with the possibility of smooth adjustment of speeds of 150, 200, 300 Baud in the range from +12 to -12%.
The error of the measuring part when measuring distortions from its own sensor at speeds up to 200 Baud when counting through 2% does not exceed ±2%, when counting through 1% - ±1%; at speeds of 200 and 300 baud, this error is ± 3% when reading through 2% and ± 2% when reading through 1%.
The operational error of the device in synchronous mode when receiving from a sensor of another device during a measurement session corresponding to the transmission of 1000 elementary parcels at a telegraphy speed of 50 baud does not exceed ±3% with a countdown of 2%, and with a countdown of 1% - ±2%.
The device registers the value of total or start-stop distortions or their maximum value for a measurement session. The device provides measurement of distortions of the fronts of each of the parcels of the start-stop cycle. The device allows you to divide the distortion into random, characteristic and predominance with the definition of their sign.
The input device of the device provides reception at speeds up to 100 Baud of rectangular and rounded packages in single-pole mode and reception of two-pole packages at all speeds. The minimum current of the input device in two-pole mode is 2 mA, in single-pole mode 5 mA.
- pressing "+";
- pressing "-";
- "1:1" (dots);
- "6:1";
- "1:6";
- the text "РЫ" according to the international code No. 2, as well as the combination of "P" and "Y" separately;
- automatically alternating combinations "5:1"
The sensor of the device has overload protection, short circuit alarm and protection against polarity reversal of linear power supplies.
The power consumed by the device at the rated mains voltage does not exceed 100 VA.
The overall dimensions of the BIR block are 225x130x125 mm. Weight 1.6 kg.
