1. Safety Measures in Super Power and High Power Transmitters in
All India Radio
R.K.Singh and V.K Gupta

2. Present Status of Transmitters in AIR
All India Radio is operating a large
Number of Transmitters ranging from
1kw to 1000kW
In addition large no of FM transmitters
are also operating
All these Transmitters radiate through
MW, SW Antennas and high FM Towers .

3. Present Status of Transmitters in AIR
Working on these Transmitters, Antennas
and very high Towers calls for great care
and safety measures to avoid accidents
And safety of very costly equipments and
operators .

4. Major components/systems involved in
Broadcasting
1.RF Chain
2.AF Chain
3.Power Supply System
4. Metering System
5.Protection System
6.Cooling System
7.Feeder Line
8.MW/SW Antenna System
9.Control System .

5. Frequency Range of Broadcasting
MW Range: 540kHz to 1605 kHz
SW Range: 3MHz to 30MHz
FM Range: 87.5MHz to 108MHz

6. Salient features of RF Chain
RF chain develops Carrier(RF) of rated Frequency
Very costly transmitting valves are used
It requires special cooling system like Condensed
Vapor cooling.
Special protection system is provided to these very
costly transmitting valves.
For example in 300 kW MW BBC transmitter the
valve used is CQK 350 costing about 25 LACS

7. Salient features of AF Chain
This chain provides desired amplification to audio
signal (content) before it is superimposed on
Carrier.
This process is known as ‘Modulation’
In the final stage of this chain costly transmitting
Valves are used
These valves are also provided special protection.
For example in 300 kW MW BBC transmitter the
valve used is CQK 50.

8. Power Supply System
This system provides DC power supply to various
stages of RF chain and AF chain.
In final stage required may be 15 KV DC or more.
In HPTs and SPTs Thyristor controlled DC power
supply is used.
This has special protection system like costly bank
of protection diodes.
This Thyristor controlled power supply must be
protected against any reflected power or transients.

9. Metering system of Broadcast Transmitter
Constant observation of voltage, current, or any
other parameters of various stages of the
transmitter, transmission line and mast/tower is
very essential to monitor the health of the
broadcast transmission system.

10. Metering system of Broadcast Transmitter
Essential voltage, current and power, temperature
, cooling water temperature/pressure are picked
up from various points and displayed on the panel
in front of the operator.
These readings are recorded manually or
automatic at regular interval.

11. Metering system of Broadcast Transmitter
One such important measurement is VSWR.
This reading gives the idea about how much
transmitter power is being radiated and how much
power is reflected back to transmitter.
This reflected power is very dangerous and may
damage costly equipments.
Readings are recorded manually or
automatic at regular interval.

12. Protection System of Broadcast Transmitter
Very fast and effective protection system is
Safe guard operators and costly equipments.
A knob in red color is provided in front panel of
the transmitter.
In case of any major problem like fire, severe
Sparking etc. this knob is pressed to switch off the
Transmitter completely.
These protection devices should be very fast.

13. Protection System of Broadcast Transmitter
In old generation transmitters electromagnetic
relays were used.
These relays were not fast acting.
Now modern generation transmitters uses digital
relays.
These solid state device relays are very fast acting.

14. Cooling System of Broadcast Transmitter
High power transmitting tubes needs very
effective cooling to protect it from damage.
Forced air cooling and water cooling were used
In old generation transmitters.
Modern transmitters use condensed vapour
Cooling which is very efficient in removing heat
from the valve and protecting it from the damage.

15. MW/SW Antenna System Broadcast Transmitter
Very high self radiating mast are used for MW
Transmitters. These masts are supported by guy
Wires and insulated from the ground by mast
Base insulator.
Verticality of the mast regular maintenance of guys
Is essential to avoid any serious accident.
SW aerial are called curtain, dipole.
These are supported in the air with the help of
towers.
Regular maintenance of Aerial field is essential.

16. Control Circuit System of Broadcast Transmitter
Control circuit of any transmitter is most important
It is called Brain of the transmitter.
It controls every operation of the transmitter like
switching on/off in defined sequence
Operators working on the transmitter must be very
familiar with the Control circuit.
Control system is important part of the safety
measures of broadcast transmitters

17. Special precautions before switching on the of Broadcast Transmitter
Operating staff work in shift in AIR.
There is over lapping period when persons of two
shifts are on duty.
It is mandatory for engineer on duty to blow
hooter for some specified time before applying
HT voltage to transmitter.
Some time technician or engineer may be working
or doing some maintenance work inside the
transmitter or in the aerial field
Hooter is to alert everyone.

18. Special precautions before starting maintenance work in the Broadcast Transmitter or in the Aerial field
Proper entry should be made in the log book.
Before touching any component in the cubicle or
In ATU it must be touched by the Earth Rod.
Cubicles and components should be examined for
any sparking spot
Components should be touched with due care for
any overheating.
Maintenance schedule must be strictly followed.

19. Special Safety features in Broadcast Transmitters
It is interesting to note that in any high power
Broadcast transmitter there is strong RF field
present in the cubicles of the transmitter, inside
The transmitter building and in the aerial field.
This RF field is capable of producing voltage of the
order of 50to100 Volts or even more.
Digital control circuit operate on 5volts.
This digital circuit gives command to operate
various stages of the high power transmitter

20. How Digital circuit is protected from strong RF field in the transmitter?
Digital control circuit is part of the transmitter and
located in one of the cubicle of the transmitter.
RF field in the cubicle can easily generate more
than 5 Volts in Digital circuit force it to give wrong
command to transmitter.
This may create malfunctioning of the transmitter
and may cause serious damage to equipment and
threat to operators.

21. What is Filter Wall? How it protects Digital circuit from strong RF field in the transmitter?
Digital control circuit is located in a cubicle which has filter walls all around.
This filter wall has large number of holes and each hole is fitted with RF bypass capacitor.
All the wires entering into the digital control circuit or going out from the control circuit has to pass through these holes fitted with RF filter condenser.
This removes any RF voltage associated with wire.
Hence Digital circuit can not malfunction.

22. Digital Broadcasting in India Introduction of DRM transmitters in AIR
About 40 DRM transmitters have been installed
At various stations of All India Radio.
These transmitters can operate in both Analog and Digital mode.
These Digital transmitters with modern technology have excellent protection devices and
Safety measures.

23. We welcome your Questions
THANKS
We welcome your Questions
R.K.Singh and V.K Gupta