25-08-2012, 01:26 PM
FACILITIES IN STUDIO CENTRE
[attachment=32726]
Introduction
The broadcast of a programme from source to listener involves use of studios, microphones, announcer console, switching console, telephone lines / STL and Transmitter. Normally the programmes originate from a studio centre located inside the city/town for the convenience of artists. The programme could be either “live” or recorded”. In some cases, the programme can be from OB spot, such as commentary of cricket match etc. Programmes that are to be relayed from other Radio Stations are received in a receiving centre and then sent to the studio centre or directly received at the studio centre through RN terminal/telephone line. All these programmes are then selected and routed from studio to transmitting centre through broadcast quality telephone lines or studio transmitter microwave/VHF links
Broadcast Studio
A broadcast studio is an acoustically treated room. It is necessary that the place where a programme for broadcast purposes is being produced should be free of extraneous noise. This is possible only if the area of room is insulated from outside sound. Further, the microphone which is the first equipment that picks up the sound, is not able to distinguish between wanted and unwanted signals and will pick up the sound not only from the artists and the instruments but also reflections from the walls marring the quality and clarity of the programme. So the studios are to be specially treated to give an optimum reverberation time and minimum noise level. The entry to the studios is generally through sound isolating lobby called sound lock. Outside of every studio entrance, there is a warning lamp, which glows ‘Red’ when the studio is ‘ON-AIR’. The studios have separate announcers booths attached to them where first level fading, mixing and cueing facilities are provided.
In addition to control room and studios, dubbing/recording rooms are also provided in a studio complex. Following equipments are generally provided in a recording/dubbing room :
i) Console tape recorders
ii) Console tape decks
iii) Recording/dubbing panel having switches, jacks and keys etc.
Announcer Console
Most of the studios have an attached booth, which is called transmission booth or Announcer booth or play back studio. This is also acoustically treated and contains a mixing console called Announcer Console. The Announcer Console is used for mixing and controlling the programmes that are being produced in the studio using artist microphones, tape playback decks and turn tables/CD players. This is also used for transmission of programmes either live or recorded.
The technical facilities provided in a typical announcer booth, besides an Announcer Console are one or two microphones for making announcements, two turn tables for playing the gramophone records and two playback decks or tape recorders for recorded programmes on tapes. Recently CD and Rotary Head Digital Audio Tape Recorder (R-DAT) are also included in the Transmission Studio.
Control Room
For two or more studios set up, there would be a provision for further mixing which is provided by a control console manned by engineers. Such control console is known as switching console. Broad functions of switching console in control room are as follows:
• Switching of different sources for transmission like News, O.Bs. other satellite based relays, live broadcast from recording studio.
• Level equalisation and level control.
• Quality monitoring.
• Signalling to the source location.
• Communication link between control room and different studios.
AMPLIFIERS USED IN AIR STUDIOS
Introduction
Amplifier is one of the basic building blocks of modern electronics. The present day electronics would not exist without this. Amplification is necessary because the desired signal is usually too weak to be directly useful. Present day amplifiers used in studios are mostly employing ICs and transistors.
Input Impedance
It is defined as the impedance which we get while looking into the input terminals of an amplifier. The input impedance of a pre-amplifier determines the amount of a.c. voltage the pre-amplifier will get from a microphone. The input impedance also decides the noise performance of the amplifier. For best noise performance, the input impedance of a pre amplifier should exceed ten times the source impedance. It is because of this reason that the input impedance of a pre amplifier is always 2000 ohm or more. In some amplifiers a bridging input is provided. This implies that the input impedance is 10,000 ohm or greater and this impedance is achieved by using a special input transformer. Bridging input permits several amplifiers to be connected across a line without upsetting the impedance match of other equipment.
Output Impedance
The actual impedance seen when looking into the output terminals of an amplifier is called its output impedance. This term should not be confused with load impedance. Load impedance is defined as a specified impedance into which a device is designed to work. Many times the load impedance is higher than the output impedance. For example the output impedance of equalised line amplifier type lab 568 is less than 50 ohm while the specified load impedance is 600 ohm.
Distortion in amplifiers
The amplification of a sinusoidal signal to the input of an ideal class - A amplifier will result in a sinusoidal output wave. Generally the output waveform is not an exact replica of the input signal waveform because of various types of distortions that may arise either from the inherent non-linearity in the characteristics of the active device or from the influence of the associated circuit. The types of distortions that may exist either separately or simultaneously are called non-linear distortion, frequency distortion and delay or phase shift distortion.
Non linear distortion: This type of distortion results from the production of new frequencies in the output which are not present in the input signal. These new frequencies or harmonics, result from the existence of non-linear dynamic curve for the active devices. The distortion is sometimes referred to as amplitude distortion or harmonic distortion. This type of distortion is more prominent when the signal levels are quite large so the dynamic operation spreads over a wide range of the characteristics.
Frequency Distortion : This type of distortion exists when the signal components of different frequencies are amplified differently. In a transistor amplifier, this type of distortion may be caused either by the internal device capacitances or it may arise because of the associated circuit such as, the coupling components. If the frequency response characteristic is not a straight line over the range of frequencies under consideration, the circuit is said to exploit frequency distortion over this range.
Phase shift or delay distortion : Phase shift distortion results from unequal phase shifts of signals of different frequencies. This type of distortion is not important in audio frequency amplifiers since the human ear is incapable of distinguishing relative phases of different frequency components. But it is very objectionable in the system that depends on the wave shape of the signal for their operation e.g. in television.
AF Final Stage
AF final stage is equipped with ceramic tetrodes CQK-25. Filament current of this tube is about 210 Amps. at 10V. The filament transformers are of special leakage reactance type and their short circuit current is limited to about 2 to 3 times the normal load current. Hence the filament surge current at the time of switching on will not exceed the maximum limit.
A varistor at the screen or spark gaps across the grid are to prevent over voltages. As the modulator valve is condensed vapour cooled tetrodes, deionised water is used for cooling. The valve required about 11.5 litres/min. of water. Two water flow switches WF1 and WF2 in the water lines of each of the valves protect against low or no water flow. Thermostats WT1 and WT2 in each water line provide protection against excessive water temp. by tripping the transmitter up to stand-by if the temperature of the water exceeds 70o C.
Modulation condenser and modulation choke have been dispensed with due to the special design of the modulation transformer. Special high power varistor is provided across the secondary winding of the modulation transformer to prevent transformer over voltages.
Connection of Load (Antenna/Dummy load)
After the application of ventilation, filament and bias the anode voltage can be switched on. But before the anode voltage can be increased the interlocking circuit is to ensure that the load of the transmitter namely antenna or dummy load is connected to the transmitter. The tuning process of the various RF stages are complete and none of the tuning motors are moving.
Application of Screen Voltage : In the case of tetrode tubes, the screen voltage to the tube should not be applied before the application of anode voltage to keep the screen current and screen dissipation within limits. This is taken care of by an interlocking provision that the screen voltage is applied only after the anode voltage reach a certain pre-determined value well above the normal screen voltage.
Release of Audio frequency : The application of AF signal to the AF stage in the absence of carrier power would result in the operation of modulation transformer with no load connected. This is not desirable. Therefore, the AF signal should be applied to the Audio frequency stages only when the RF power amplifier is delivering the nominal power. Normally AF frequency signal to the AF stage is released only when the carrier power is approximately 80% of the normal power.
[attachment=32726]
Introduction
The broadcast of a programme from source to listener involves use of studios, microphones, announcer console, switching console, telephone lines / STL and Transmitter. Normally the programmes originate from a studio centre located inside the city/town for the convenience of artists. The programme could be either “live” or recorded”. In some cases, the programme can be from OB spot, such as commentary of cricket match etc. Programmes that are to be relayed from other Radio Stations are received in a receiving centre and then sent to the studio centre or directly received at the studio centre through RN terminal/telephone line. All these programmes are then selected and routed from studio to transmitting centre through broadcast quality telephone lines or studio transmitter microwave/VHF links
Broadcast Studio
A broadcast studio is an acoustically treated room. It is necessary that the place where a programme for broadcast purposes is being produced should be free of extraneous noise. This is possible only if the area of room is insulated from outside sound. Further, the microphone which is the first equipment that picks up the sound, is not able to distinguish between wanted and unwanted signals and will pick up the sound not only from the artists and the instruments but also reflections from the walls marring the quality and clarity of the programme. So the studios are to be specially treated to give an optimum reverberation time and minimum noise level. The entry to the studios is generally through sound isolating lobby called sound lock. Outside of every studio entrance, there is a warning lamp, which glows ‘Red’ when the studio is ‘ON-AIR’. The studios have separate announcers booths attached to them where first level fading, mixing and cueing facilities are provided.
In addition to control room and studios, dubbing/recording rooms are also provided in a studio complex. Following equipments are generally provided in a recording/dubbing room :
i) Console tape recorders
ii) Console tape decks
iii) Recording/dubbing panel having switches, jacks and keys etc.
Announcer Console
Most of the studios have an attached booth, which is called transmission booth or Announcer booth or play back studio. This is also acoustically treated and contains a mixing console called Announcer Console. The Announcer Console is used for mixing and controlling the programmes that are being produced in the studio using artist microphones, tape playback decks and turn tables/CD players. This is also used for transmission of programmes either live or recorded.
The technical facilities provided in a typical announcer booth, besides an Announcer Console are one or two microphones for making announcements, two turn tables for playing the gramophone records and two playback decks or tape recorders for recorded programmes on tapes. Recently CD and Rotary Head Digital Audio Tape Recorder (R-DAT) are also included in the Transmission Studio.
Control Room
For two or more studios set up, there would be a provision for further mixing which is provided by a control console manned by engineers. Such control console is known as switching console. Broad functions of switching console in control room are as follows:
• Switching of different sources for transmission like News, O.Bs. other satellite based relays, live broadcast from recording studio.
• Level equalisation and level control.
• Quality monitoring.
• Signalling to the source location.
• Communication link between control room and different studios.
AMPLIFIERS USED IN AIR STUDIOS
Introduction
Amplifier is one of the basic building blocks of modern electronics. The present day electronics would not exist without this. Amplification is necessary because the desired signal is usually too weak to be directly useful. Present day amplifiers used in studios are mostly employing ICs and transistors.
Input Impedance
It is defined as the impedance which we get while looking into the input terminals of an amplifier. The input impedance of a pre-amplifier determines the amount of a.c. voltage the pre-amplifier will get from a microphone. The input impedance also decides the noise performance of the amplifier. For best noise performance, the input impedance of a pre amplifier should exceed ten times the source impedance. It is because of this reason that the input impedance of a pre amplifier is always 2000 ohm or more. In some amplifiers a bridging input is provided. This implies that the input impedance is 10,000 ohm or greater and this impedance is achieved by using a special input transformer. Bridging input permits several amplifiers to be connected across a line without upsetting the impedance match of other equipment.
Output Impedance
The actual impedance seen when looking into the output terminals of an amplifier is called its output impedance. This term should not be confused with load impedance. Load impedance is defined as a specified impedance into which a device is designed to work. Many times the load impedance is higher than the output impedance. For example the output impedance of equalised line amplifier type lab 568 is less than 50 ohm while the specified load impedance is 600 ohm.
Distortion in amplifiers
The amplification of a sinusoidal signal to the input of an ideal class - A amplifier will result in a sinusoidal output wave. Generally the output waveform is not an exact replica of the input signal waveform because of various types of distortions that may arise either from the inherent non-linearity in the characteristics of the active device or from the influence of the associated circuit. The types of distortions that may exist either separately or simultaneously are called non-linear distortion, frequency distortion and delay or phase shift distortion.
Non linear distortion: This type of distortion results from the production of new frequencies in the output which are not present in the input signal. These new frequencies or harmonics, result from the existence of non-linear dynamic curve for the active devices. The distortion is sometimes referred to as amplitude distortion or harmonic distortion. This type of distortion is more prominent when the signal levels are quite large so the dynamic operation spreads over a wide range of the characteristics.
Frequency Distortion : This type of distortion exists when the signal components of different frequencies are amplified differently. In a transistor amplifier, this type of distortion may be caused either by the internal device capacitances or it may arise because of the associated circuit such as, the coupling components. If the frequency response characteristic is not a straight line over the range of frequencies under consideration, the circuit is said to exploit frequency distortion over this range.
Phase shift or delay distortion : Phase shift distortion results from unequal phase shifts of signals of different frequencies. This type of distortion is not important in audio frequency amplifiers since the human ear is incapable of distinguishing relative phases of different frequency components. But it is very objectionable in the system that depends on the wave shape of the signal for their operation e.g. in television.
AF Final Stage
AF final stage is equipped with ceramic tetrodes CQK-25. Filament current of this tube is about 210 Amps. at 10V. The filament transformers are of special leakage reactance type and their short circuit current is limited to about 2 to 3 times the normal load current. Hence the filament surge current at the time of switching on will not exceed the maximum limit.
A varistor at the screen or spark gaps across the grid are to prevent over voltages. As the modulator valve is condensed vapour cooled tetrodes, deionised water is used for cooling. The valve required about 11.5 litres/min. of water. Two water flow switches WF1 and WF2 in the water lines of each of the valves protect against low or no water flow. Thermostats WT1 and WT2 in each water line provide protection against excessive water temp. by tripping the transmitter up to stand-by if the temperature of the water exceeds 70o C.
Modulation condenser and modulation choke have been dispensed with due to the special design of the modulation transformer. Special high power varistor is provided across the secondary winding of the modulation transformer to prevent transformer over voltages.
Connection of Load (Antenna/Dummy load)
After the application of ventilation, filament and bias the anode voltage can be switched on. But before the anode voltage can be increased the interlocking circuit is to ensure that the load of the transmitter namely antenna or dummy load is connected to the transmitter. The tuning process of the various RF stages are complete and none of the tuning motors are moving.
Application of Screen Voltage : In the case of tetrode tubes, the screen voltage to the tube should not be applied before the application of anode voltage to keep the screen current and screen dissipation within limits. This is taken care of by an interlocking provision that the screen voltage is applied only after the anode voltage reach a certain pre-determined value well above the normal screen voltage.
Release of Audio frequency : The application of AF signal to the AF stage in the absence of carrier power would result in the operation of modulation transformer with no load connected. This is not desirable. Therefore, the AF signal should be applied to the Audio frequency stages only when the RF power amplifier is delivering the nominal power. Normally AF frequency signal to the AF stage is released only when the carrier power is approximately 80% of the normal power.