AM and FM Transmitters and receivers

High Level modulation, Low Level modulation, AM transmitter, AM superheterodyne receiver, FM transmitter, Armstrong method of FM generation

1. Transmitters and receivers 14 Marks Ms. Kavita Giri Lecturer ( ET) Government Residential Womens Polytechnic , Latur

2. Learning Outcomes Explain with sketches the working of given type of AM generation technique. Explain the function of given blocks of AM super heterodyne receiver. Explain with sketches given type of AM demodulation technique. Explain with sketches principle of given type of FM generation technique. Compare the working of given type of FM detectors. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

3. Contents 3.1 Generation of AM 3.2 Block diagram of AM super heterodyne receiver and its working with waveforms. 3.3 Demodulation of AM : Diode detector and Practical Diode detector 3.4 Automatic gain control and its types 3.5 Concept of Pre-emphasis and De-emphasis 3.6 Generation of FM using direct and indirect method 3.7 Block diagram of FM receiver and its working with waveforms. 3.8 FM detector circuits: Ratio detector and PLL as FM detector 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

4. 3.1 AM generation AM Modulators 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

5. .….3.1 AM generation 3.1.1 Low Level AM Modulator FET acts as a variable resistance Op-amp as a non-inverting amplifier 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

6. .….3.1 AM generation 3.1.1 Low Level AM Modulator 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

7. .…. 3.1 AM generation 3.1.2 Principle of High level modulation Property of a tuned Circuit If we apply a current pulse to a tuned circuit, then it generates damped voltage oscillations at its output. The amplitude of oscillations is proportional to the size of current pulse and the decay rate is proportional to the time constant. EC403E – Basics of Communication Ms. Kavita Giri, Lecturer (EC), Govt. Polytechnic, Nagpur 22334 – Principles of Electronic Communication Ms. Kavita Giri, Lecturer (ET), GRWP, Latur

8. .…. 3.1 AM generation 3.1.3 Requirements of High level modulation A tuned Circuit A circuit which supplies current pulses to the tuned circuit If the amplitude of current pulses is made proportional to the modulating signal, then AM wave will be generated at the output of the tuned circuit. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

9. .…. 3.1 AM generation 3.1.4 High level collector modulator 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

10. .…. 3.1 AM generation 3.1.4 High level collector modulator 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

11. .….3.1 AM generation 3.1.4 High level collector modulator 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

12. .….3.1 AM generation 3.1.4 High level collector modulator 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

13. .….3.1 AM generation 3.1.5 Advantages of High level collector modulator Better linearity Higher efficiency Higher output power per transistor 3.1.6 Limitations of High level collector modulator It wont be possible to get 100% modulation using this circuit. To get 100% modulation, Em = Vcc When the modulating signal goes negative, it subtracts from the Vcc . At the negative peak point, the subtraction is zero, so zero voltage is applied to transistor Q1 producing zero output. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

14. AM transmitters 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

15. AM transmitters Low Level Modulated AM Transmitter AF modulating Signal Stabilized RF crystal oscillator Class A Buffer amplifier Modulator Linear Amplifier Power amplifier Audio processing and filtering Class A AF amplifier 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

16. …… AM transmitters Low Level Modulated AM Transmitter 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

17. ….. AM transmitters High Level modulated AM Transmitter Stabilized RF crystal oscillator Class A RF amplifier Class C RF power amplifier Class C RF output amplifier Audio processing and filtering Class A AF amplifier Class B AF power amplifier AF modulating signal 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

18. ….. AM transmitters High Level modulated AM Transmitter 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

19. ….. AM transmitters Comparison of Low level and High level modulation Sr. No. Parameter Low level modulation High level modulation 1 Modulation takes place at Low power level High power level 2 Types of amplifiers Linear amplifiers (A, AB or B) are used after modulation Highly efficient class C amplifiers 3 Efficiency Lower than high level modulators Very high 4 Devices used Transistors, JFET, Op-Amps Vacuum tubes or transistors for medium power applications 5 Design of AF power amplifier Easy as low power involved Complex due to high power involved 6 Applications Sometimes used in TV transmitters High power broadcast transmitters 7 Power handling capacity Low High 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

20. 3.2 Super hetrodyne Receiver Superheterodyne is basically a process of designing and constructing wireless communications such as radio receivers by mixing two frequencies together in order to produce a difference frequency component called as intermediate frequency (IF), so as to reduce signal frequency prior to processing. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

21. 6.2.2 Superhetrodyne Receiver Receiving antenna : The receiving antenna receives the signal which was sent by the transmitter. It sends the received signal for further processing. RF amplifier : The received signal is fed to the RF amplifier stage so as to amplify it, as the signal gets attenuated during long-distance transmission. It is tuned in such a way that it can choose the desired carrier frequency and amplify it. Local Oscillator : This circuit basically generates a signal with a fixed frequency and the output is then fed to the mixer. When we talk about  AM broadcast  system, the intermediate frequency is  455 KHz  that simply means that local oscillator should select such a frequency which is 455 KHz above the incoming signal frequency. ….3.2 Super hetrodyne Receiver 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

22. 6.2.2 Superhetrodyne Receiver Mixer : A mixer simply mixes the carrier frequency with the frequency of the signal generated by the local oscillator. Here, two different frequencies are to be mixed so as to have another frequency component of lower value. Now the thing that first comes to our mind is why the mixer produces a lower frequency value, which is the difference between the two frequencies. The summation of the carrier and local oscillator frequency at the output of the mixer will give rise to image frequency which is treated as a type of noise or distortion in the signal. This is the reason why the mixer generates a frequency difference at its output. This difference frequency is a constant value irrespective of the variations in the input, known as the intermediate frequency. The constant frequency at its output is gained by capacitance tuning. In capacitance tuning, several capacitances are arranged together and operated by a controlling knob. It doesn’t matter what the incoming signal frequency is, the RF amplifier and local oscillator must be tuned to it. ….3.2 Super hetrodyne Receiver 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

23. 6.2.2 Superhetrodyne Receiver IF amplifie r: This section basically amplifies the output of the mixer. IF amplifier provides sensitivity(gain) and selectivity (bandwidth requirement) to the receiver. As it consists of several transformers consisting of pairs of the tuned circuit . Here , the sensitivity and selectivity are uniform and does not show variations as in case of TRF receivers because  IF amplifier’s characteristics are independent of that of the received signal frequency  as it works on the intermediate frequency. Due to this, the system design is quite easy so as to provide constant bandwidth along with high gain . This section has narrow bandwidth and due to its lower bandwidth, it rejects all other frequency so as to reduce the risk generated from interference. The lower bandwidth accepting nature supports Superheterodyne receivers to give much better performance than other types of receivers. ….3.2 Super hetrodyne Receiver 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

24. 6.2.2 Superhetrodyne Receiver Demodulato r: Demodulator is placed exactly after the IF amplifier so that the constant frequency signal is demodulated and the message signal can be extracted from it. Audio amplifie r: The original signal is fed to the audio amplifier which does not hold distortion or noise so that it can amplify audio signal to a particular level. Power amplifier : Here, the signal is further amplified to a particular power level which can activate the loudspeaker. The amplified signal is finally fed to the loudspeaker circuit which converts the electrical form of the signal into an audio sound signal which can be heard by the listeners. ….3.2 Super hetrodyne Receiver 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

25. 6.2.2 Superhetrodyne Receiver Summary of superheterodyne action ….3.2 Super hetrodyne Receiver 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

26. Waveforms at different points of superheterodyne receiver ….3.2 Super hetErodyne Receiver 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

27. Advantages No variation in bandwidth. The bandwidth remains constant over the entire operating range. High sensitivity and selectivity. High adjacent channel rejection. Frequency Parameters of AM Receivers Frequency bands: a. Medium wave (MW) band b. Short Wave (SW) band RF Carrier Range : a. 535 KHz to 1650 KHz (MW Band) b. 5 to 15 MHz (SW Band) 3. Intermediate Frequency IF : 455 KHz 4. IF bandwidth B : 10KHz ….3.2 Super hetrodyne Receiver 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

28. The process of detection is also called as demodulation. It is the process exactly opposite to modulation. 3.3 Demodulation of am signals The process of recovering the message signal from the received modulated signal is called as detection / demodulation. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

29. 3.3 types of am detectors 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

30. Simple and efficient method for demodulation of narrowband AM signals. A narrowband AM is one in which carrier frequency f c is much higher than bandwidth of the modulating signal. An envelope demodulator produces an output signal that follows the envelope of the input AM signal exactly. It is used in all the commercial AM radio receivers. 3.3 AM Detectors 3.3.1 Envelope Detector 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

31. The envelope demodulator consists of a diode and RC filter. …..3.3 AM Detectors 3.3.1 Envelope Detector 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

32. …..3.3 AM Detectors 3.3.1 Envelope Detector 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

33. …..3.3 AM Detectors 3.3.1 Envelope Detector It shows the charging  discharging of the filter capacitor and the approximate output voltage . It may be observed from these waveforms that the envelope of the AM wave is being recovered successfully . 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

34. …..3.3 AM Detectors 3.3.1 Envelope Detector Selection of RC time constants The capacitor charges through D and R s   when the diode is on and it discharges through R when the diode is off . The charging time constant  R s C should be short compared to the carrier period 1/f c  . Thus,       R s C << 1/f c On the other hand, the discharging time constant RC should be long enough so that the capacitor discharges slowly through the load resistance R . But , this time constant should not be too long which will not allow the capacitor voltage to discharge at the maximum rate of change of the envelope . Therefore,             1/f c  << RC <<  1/W where, W = Maximum modulating frequency 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

35. …..3.3 AM Detectors 3.3.1 Envelope Detector Distortions in envelop detector There are two types of distortions which can occur in the detector output such as : 1. Diagonal clipping 2. Negative peak clipping 1. Diagonal Clipping This type of distortion occurs when the RC time constant of the load circuit is too long. Due to this, the RC circuit cannot follow the fast changes in the modulating envelope .  22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

36. …..3.3 AM Detectors 3.3.1 Envelope Detector 2. Negative peak Clipping This distortion occurs due to a fact that the modulation index on the output side of the detector is higher than that on its input side. Hence, at higher depth of modulation of the transmitted signal, the overmodulation may take place at the output of the detector. The negative peak clipping will take place as a result of this overmodulation .   22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

37. …..3.3 AM Detectors 3.3.2 Practical Diode Detector 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

38. …..3.3 AM Detectors 3.3.2 Practical Diode Detector 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur The diode has been reversed, so that now the negative envelope is demodulated. This has no effect on detection, but it does ensure that a negative AGC voltage will be available. The resistor R of the basic circuit has been split into two parts R1 and R2 to ensure that there is a series DC path to ground for the diode

39. …..3.3 AM Detectors 3.3.2 Practical Diode Detector 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur A low pass filter has been added, in the form of R1-C1. This has the function of removing any RF ripple that might still be present. Capacitor C2 is coupling capacitor, which is used to prevent the diode dc output from reaching the volume control R4. R3-C3 is a low pass filter to the carrier strength, and which may be used for automatic gain control

40. 3.4 Automatic Gain control (AGC) 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur The signals from various radio stations reaching at the receiver input are not of same strength. The signals from strong stations are strong and those from weak stations are weak. If the receiver gain is constant then the receiver output will fluctuate proportional to the strength of input signal. This is not desirable. So the automatic gain control is used to adjust the receiver gain automatically so as to keep the receiver output constant irrespective of strength of input signal. Types of AGC

41. 3.4 Automatic Gain control 3.4.1 Simple AGC 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur Simple AGC is a system which will change the overall gain of a receiver automatically. This is done in order to keep the receiver output constant even when the signal strength at the input of the receiver is changing. In the AGC system, a dc voltage (AGC bias) is derived from the detector. This AGC bias is thus proportional to the strength of the received signal. The AGC bias is applied to a selected number of RF and IF amplifiers and mixer stage. The transconductance and hence the gain of the devices connected to these stages is dependent on the applied AGC bias.

42. 3.4 Automatic Gain control AGC Characteristics 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur Advantages of Simple AGC Simplicity Low cost. Hence used in domestic radio receivers. Disadvantages of Simple AGC Not only strong signals and the weak signals also are attenuated.

43. 3.4 Automatic Gain control 3.4.2 Delayed AGC 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur Ideal AGC N o Delayed Automatic Gain Control would be applied until signal strength was considered adequate, and after this point a constant average output would be obtained no matter how much more the signal strength rose.

44. 3.4 Automatic Gain control 3.4.2 Delayed AGC 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur Delayed Automatic Gain Control curve. This shows that AGC bias is not applied until the signal strength has reached a predetermined level, after which bias is applied as with normal AGC, but more strongly. As the signal strength then rises, receiver output also rises, but relatively slightly. The problem of reducing the gain of the receiver for weak signals has thus been avoided, as with “ideal” AGC

45. 3.4 Automatic Gain control 3.4.2 Delayed AGC 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

46. 3.4 Automatic Gain control 3.4.2 Delayed AGC 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur It uses two separate diodes: the detector and the AGC detector . These can be connected either to separate transformer winding, as shown, or both may be connected to the secondary without too much interference. A positive bias is applied to the cathode of the AGC diode, to prevent conduction until a predetermined signal level has been reached. A control is often provided, as shown, to allow manual adjustment of the bias on the AGC diode, and hence of the signal level at which Delayed Automatic Gain Control is applied. If weak stations are mostly likely to be received, the delay control setting may be quite high (i.e., no AGO until signal level is fairly high). Nevertheless , it should be made as low as possible, to prevent overloading of the last IF amplifier by unexpected stronger signals.

47. 3.5 Pre-emphasis & de-emphasis in fm Pre-Emphasis Why Pre-Emphasis??? 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

48. …..3.5 Pre-emphasis & de-emphasis in fm Pre-Emphasis The artificial boosting of higher modulating frequencies is called as pre-emphasis. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

49. Pre-Emphasis The pre-emphasis circuit is basically a high pass filter. The pre-emphasis is carried out at the transmitter . The frequency for the RC high pass network is 2122 Hz as shown in fig.1 (b). Hence , the pre-emphasis circuit is used at the transmitter as shown in fig.2. …..3.5 Pre-emphasis & de-emphasis in fm 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

50. De-Emphasis The process that is used at the receiver end to nullify or compensate the artificial boosting given to the higher modulating frequencies in the process of pre-emphasis is called De-emphasis. That means, the artificially boosted high frequency signals are brought to their original amplitude using the de-emphasis circuit . The 75 μsec de-emphasis circuit is standard and it is as shown in fig. 3. It shows that it is a low pass filter. 75 μsec de-emphasis corresponds to a frequency response curve that is 3 dB down at a frequency whose RC time constant is 75 μsec.i.e ., The demodulated FM is applied to the De-emphasis circuit. With increase in f m the reactance of C goes on decreasing and the output of de-emphasis circuit will also reduce as shown in fig.3. …..3.5 Pre-emphasis & de-emphasis in fm

51. 3.6 Generation of FM waves 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

52. 3.6 Generation of FM waves Direct Method of FM Generation In direct method or parameter variation method, the baseband or modulating signal directly modulates the carrier. The carrier signal is generated with the help of an oscillator circuit. This oscillator circuit uses a parallel tuned L-C circuit. Thus the frequency of oscillation of the carrier generation is governed by the expression : Now, we can make the carrier frequency ω c  to vary in accordance with the baseband or modulating signal x(t) if L or C is varied according to x(t ). 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

53. A) Reactance Modulator In direct FM generation, the instantaneous frequency of the carrier is changed directly in proportion with the message signal. For this, a device called voltage controlled oscillator (VCO) is used. A VCO can be implemented by using a sinusoidal oscillator with a tuned circuit having a high value of Q. Principle of Working 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur 3.6.1 Direct Method of FM Generation

54. Varactor Diode Modulator Principle of Working A varactor diode is a semiconductor diode whose junction capacitance varies linearly with the applied bias and the varactor diode must be reverse biased. 3.6.1 Direct Method of FM Generation

55. Advantages Simple Circuits Low Cost Disadvantages The LC oscillator frequency is not stable enough. Oscillator cannot be used for broadcast purposes. Crystal Oscillator needs to be used. We have to use automatic frequency control scheme. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur 3.6.1 Direct Method of FM Generation

56. Armstrong Frequency Modulation System In this method, the FM is obtained through phase modulation. A crystal oscillator can be used hence the frequency stability is very high and this method is widely used in practice. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur 3.6.2 inDirect Method of FM Generation

57. Armstrong Frequency Modulation System This method needs to be divided into three parts: 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur 3.6.2 inDirect Method of FM Generation

58. Armstrong Frequency Modulation System Part I: How to obtain FM from phase modulator? 3.6.2 inDirect Method of FM Generation

59. Armstrong Frequency Modulation System Part II: Implementation of Phase modulator 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur 3.6.2 inDirect Method of FM Generation

60. Armstrong Frequency Modulation System Part II: Implementation of Phase modulator 3.6.2 inDirect Method of FM Generation 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

61. Armstrong Frequency Modulation System Part II: Implementation of Phase modulator Now, as the modulation index is increased, the amplitude of sidebands will also increase. Hence, the amplitude of their resultant increases. This will increase the angle Φ made by the resultant with unmodulated carrier. 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur 3.6.2 inDirect Method of FM Generation

62. Armstrong Frequency Modulation System Part III : Combining Parts I and II 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur 3.6.2 inDirect Method of FM Generation

63. Block Diagram 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur 3.7 FM receiver RF Amplifier Local Oscillator Mixer IF Amplifier Limiter FM Detector De-emphasis AF and Power amplifier Receiving Antenna It also works on the principle of ‘ Super heterodyning ’ as in AM receivers Difference between AM and FM receivers: The operating frequencies in FM are much higher than in AM. FM receivers need limiter and de-emphasis FM demodulators are different than AM. Method to obtain AGC is different.

64. Working 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur 3.7 FM receiver

65. Waveforms at various points of FM receiver 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur 3.7 FM receiver

66. An FM detector or demodulator is a circuit which receives an FM wave at its input and produces the message signal or modulating signal at its output. Demodulation or detection is exactly opposite to the modulation process. The AM detector is basically an envelope detector. But FM detector is basically a frequency to amplitude converter. It is expected to convert the frequency variations in FM wave at its input into amplitude variations at its output to recover the original modulating signal. 3.8 FM detectors 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

67. Requirements of FM detector 1 2 3 4 3.8 FM detectors 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur

68. Types of FM detectors 3.8 FM detectors 22334 – Principles of Electronic Communication Ms. Kavita Giri , Lecturer (ET), GRWP, Latur