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Index
1. Introduction to VSP
a. Introduction to communication
b. Role of communication
c. Types of communication systems
d. Objective
2. Coke ovens & vhf system
a. Block diagram
3. Construction
a. Description in detail
Receiver
Transmitter
Microprocessor control
Synthesizer
Phase locked loop
Phase comparator
Voltage controlled oscillator
EPROM
Signaling
Power supply and Reset
Switched mode power supply
Control and Display
4.Technical specifications
5. Additional features of the base station
6. Programming of the base station
7. Trouble shooting of the base station
8. Suggested applications of the vhf systems
9. Conclusion
1. Introduction to VSP:
Visakhapatnam steel plant is the only shore based integrated steel
plant in our country. Smt.Indira Gandhi laid the foundation stone fulfilling the long
cherished dream of the people of Andhra Pradesh.
Due to the past experience it was realized that in order to be viable,
this plant need to operate at high levels of efficiency comparable with international
standards. It is also necessary that the plant reach its rated capacities at the shortest
possible time. For achieving this it is essential that this plant be characterized as
one having
a) Minimum manpower
b) Better discipline
c) Good team work.
The blue print of Visakhapatnam Steel Plant described the plant as the most
modern Steel plant employing new technologies - very best in the industry with
latest instrumentation and introduction of computerization on large scale.
Visakhapatnam steel plant is located 15 Kms to the South West of the
Visakhapatnam Port. It lies between the Northern boundary of the National
Highway No. 5 from Madras to Calcutta and 7 Kms to the South West of Howrah
Madras railway line.
b) MAJOR PRODUCTION FACILITIES:
VSP has the following major production facilities:
4 coke oven batteries of 67 ovens each and 41.7 cu mt Volume
2 Sinter machines of 312 sq mt area
2 Blast furnaces of 3200 cu mt useful volume
SMS with 3 LD converters of 150 ton capacity and 6 nos of 4 strand
continuous bloom casters
Light and medium merchant mill of 7,10,000 tons per year capacity
Wire rod mill of 8,50,000 tons per year capacity
Medium Merchant & Structural mill of 8,50,000 tons per year capacity
i) Coke Oven and Coke Chemicals Plants:
Coke oven plant consists of three coke oven batteries of 67 ovens each
with useful coke chamber volume of 41.6 cubic meter. Each battery is of 7 meters
height. It produces coke in the sizes of 25 to 70 mm, which meet the coke
requirement of the Blast furnaces. The annual capacity of the three batteries is
2.261 mt. During production operation the CO gas (carbon monoxide) generated is
used in the Coke chemical plants to extract different byproducts like Benzol,
Ammonium Sulphate, Tar products etc. After extracting all the valuable products
the remaining gas is used as an energy source.
ii) Sinter Plant:
There are two sinter machines each of 312-sqmt-grate area. Here iron ore
fines, coke breeze, lime stone, dolomite are mixed together to from the
agglomerated mass, called gross sinter which is used in Blast Furnaces as the
primary input. The annual production capacity is 5.256 mt.
iii) Blast Furnace (BF):
There are two Blast Furnaces named "GODAVARI" and "KRISHNA", each
of 3200 cubic meter useful volumes. Here hot metal is produced from the raw
materials like iron ore (Lump), sinter, coke and limestone etc. The annual capacity
of this facility is 3.4 mt. From molten hot metal pig iron / steel is produced.
iv) Steel melting shop (SMS):
There are three nos. of LD converters each of 133 cubic meters with a
capacity to produce 3 mt of liquid steel. The production capacity of a plant is its
capacity to produce liquid steel. VSP is a 3-mt plant. SMS also has six number of
four strand continuous casting machines to produce blooms. 2.82 mt of blooms can
be cast annually. In this shop hot metal from BF is received in the mixer, kept for
temporary storage and transferred to converter where charging takes place in
presence of 99.5% pure oxygen. After Argon rinsing the molten steel is moved
from here to the six strand continuous casting machines. Blooms are formed which
form the input material for the mills. Blooms are also taken as input to small steel
making industries.
V) Rolling Mills (RM):
There are three rolling mills in VSP
Light & Medium merchant mills : It includes the billet mill and bar mill. It has a
two-strand rolling mill. It produces billets, bars and structures. The annual
capacity is 1.857 mts of billets and 7.1 mt of bars & structures.
Wire Rod mill : It is a high-speed four strand continuous mill. The mill is
designed to produce wire rods in plain rounds and ribbed bars (5.5 to 12.7 mm
diameter). The annual capacity of wire rods production is 0.8 mt.
Medium and Merchant mill : This mill produce squares 12 to 65mm, flats 30 to
150mm, channels and angles etc. This mill has an annual capacity of 0.85 mt of
bars and structures.
1) INTRODUCTION TO COMMUNICATION SYSTEMS:
Communication System refers to sending, receiving and processing of
information from one point to another point. A modern communication system is
first concerned with sorting, processing and storing of information before its
transmission .The processing involves conversion of voice signal into an electric
signal and then transmitted. The message need not be voice alone; it can be data,
image or a mixture of all the three forms of data.
The signal transformation process generally goes through the following steps.
The information signals are first compensated for frequency distortions.
The signals are then amplified so that they can be suitably modulated.
The modulated signal is boosted to sufficient levels to overcome the
effects of noise.
The signals are then passed onto an aerial system where these are
converted from electrical energy to electromagnetic energy.
At the receiving end the receiving system should be capable of recognizing
the signal and then capable of compensating the signal loss and provide a faithful
reproduction of the transmitted information at useful levels.
The receiving end consists of an aerial to receive the electromagnetic
energy and convert it into electrical signals.
Sensitive circuitry to recognize the signal, demodulate the signal and
compensate for distortions introduced by the channel.
Amplify the signal to audible levels.
In this modern age of industrialization and automation, telecommunication
play a very vital role in achieving the assigned targets and accomplishing the
desired performance in any organization, this is more so in case of an integrated
steel plant where the effective, efficient and reliable flow of information and
communication between different production shops, maintenance and service
departments.
Modulation:
Modulation is defined as the process by which some characteristics, usually
amplitude, frequency or phase, of a sinusoidal voltage is varied in accordance with
the instantaneous value of some other voltage called the modulating voltage.
The term carrier is applied to the voltage whose characteristic is varied and
the term modulating voltage is used for the voltage in accordance with which the
variation is made. Usually the modulation frequency is considerably lower than the
carrier frequency.
Need for Modulation:
There are two alternatives to the use of a modulated carrier for the
transmission of messages over long distance in the radio channel. Several
difficulties are involved in the propagation of electromagnetic waves at audio
frequencies below 20 Kilohertz. For efficient radiation and reception the
transmitting and receiving antennas would have to have heights comparable to a
quarter wavelength of the frequency used. All sound is concentrated within the
range from 20Hz to 20 KHz, so that all signals from the different sources would be
hopelessly and inseparably mixed up. In any city, the broadcasting stations alone
would completely blanket the “air”, and yet they represent a very small proportion
of the total number of transmitters in use.
In order to separate the various signals, it is necessary to convert them all the
different portions of the electromagnetic spectrum. Each must be given its own
frequency location. This overcomes the difficulties of poor radiation at low
frequencies and reduces interference. Once signals have been translated, a tuned
circuit is employed in the front end of the receiver to make sure that the desired
section of the spectrum is admitted and all the unwanted ones are rejected. The
tuning of such a circuit is normally made variable so that the receiver can select
any desired transmission within a predetermined range, such as the VHF broad cost
band used for frequency modulation. Separation of signals has removed many
difficulties in the absence of modulation. An unmodulated carrier has constant
maximum amplitude, a constant frequency and a constant phase relationship. In a
continuous modulation system, one of the parameters of the carrier is caused to
vary. Thus at any instant its deviation from the unmodulated value is proportional
to the instantaneous value of the modulating voltage, and the rate at which this
deviation takes place is equal to the modulating frequency.
Levels of modulation: (figures –td 60, 61)
In low-level modulation little power is associated with either the signal or
the carrier. The output of the modulator is at a lower level. A series of linear
power amplifiers are then used to boost the signal level to higher levels.
In high-level modulation the carrier and information signals are amplified to
sufficiently higher levels before modulation. This requires amplifiers, which are
linear over a wide range of frequencies.
Modulation techniques:
Among the available types of modulation techniques, Amplitude
modulation, Phase modulation and Frequency modulation are most popular.
Modulation is the process of converting a signal from its primary form to a form,
which is most suitable for transmission. This is realized by using a high frequency
signal as ‘carrier’ and varying one of its parameters like amplitude or phase or
frequency as a linear function of the instantaneous value of the modulating signal
the ‘message’. At the receiver end the reverse modulation ‘de-modulation
techniques are employed to extract the signal ‘message’ .
In all these three techniques the frequency component of the modulating
signal would occupy a different frequency component of the frequency spectrum in
the modulated form. All the above are linear modulation techniques.
Amplitude Modulation:
In amplitude modulation, the amplitude of the carrier voltage is varied in
accordance with the instantaneous value of the modulating voltage.
The unique feature of this type of modulation is that the envelope of the
modulated carrier signal has the same shape as that of the modulating signal.
Amplitude modulation requires that
a) Carrier frequency is very much higher than that of the modulating
signal
b) The amplitude of the modulating signal is less than that of the carrier
In case the above two conditions are not met, it would result in distortion of
the received signal. The detection of signal from AM signals uses two types of
methods, they are coherent / synchronous detection, de-multiplier techniques or
diode / envelope detection. Amplitude modulation results in generation of USB
and LSB (the upper and lower side bands).
Frequency Modulation:
Frequency modulation consists in varying the frequency of the carrier
voltage in accordance with the instantaneous value of the modulating voltage
In cases where noise levels are inherent with signal in relatively large amplitudes
FM is used. FM is a non-linear or exponential technique and helps to discriminate
wanted and unwanted components of the signal in the post modulated spectrum.
Due to its non-linear nature the signals are required to be processed for
compensation.
Phase Modulation:
Phase modulation consists in varying the phase angle of the carrier voltage
in accordance with the instantaneous value of the modulating voltage.
Apart from the above pulse modulation is becoming popular due to its high signal
to noise ratio. The parameters of amplitude and frequency are varied and thus pulse
amplitude modulation, pulse width modulation, time division multiplexing,
frequency shift keying etc have come into existence.
Pre-emphasis and De-emphasis:
The boosting of the higher modulating frequencies, in accordance with a
prearranged curve, is termed Pre-emphasis and the compensation at the receiver is
called De-emphasis. Take two modulating signals having the same initial
amplitude, and one of them is pre-emphasized to twice this amplitude, other is
unaffected (being at lower freq). The receiver has to de-emphasize the first signal
by a factor of 2, to ensure that both signals have the same amplitude in the O/p of
the receiver. When this signal is de-emphasized, any noise sideband voltages are
de-emphasized with it, and therefore have lower amplitude than they would have
had without emphasis. There effect on the O/p is reduced. The higher modulating
frequencies must not be over emphasized. The curves of figure show that a 15KHz
signal is Pre-emphasized by about 17dB. When such boosting is applied the
resulting signal cannot over-modulate the carrier by exceeding the 75KHz
deviation, or distortion will be introduced. It is difficult to introduce Pre-emphasis
and de-emphasis in existing AM services since extensive modifications would be
needed, particularly in view of the huge numbers of receivers in use.
Propagation of Electromagnetic waves:
In an earth environment, electromagnetic waves propagate in ways that
depends not only on their own properties but also on those of the environment
itself since the various methods of Propagation it depends largely on frequency, the
complete electromagnetic spectrum shown in figure.
There are five different types of wave propagation as given below. The most
important of these are the ground wave (surface wave), sky wave and space wave
propagation. The Earth, the atmosphere and the frequency of signal generally
govern the propagation.
The direct wave due to line of sight propagation between the radiator and
receiver.
The reflected wave arrival after reflection at an intermediate point on the
earth’s surface.
The surface wave produced by energy traveling close to the ground and
guided by it to follow the curvature of the earth, subject to laws of
diffraction.
Ionospheric wave (sky wave) leaving the transmitter aerial in an upward
direction and being bent by the conduction layers of the atmosphere to reach
earth.
Frequency and method of propagation:
< 500 KHz Surface wave
500 KHz to 1.5 MHz Surface wave for shorter distances and
Ionosphere wave for longer distances.
1.5 MHz to 30MHz Ionospheric wave
> 30 MHz Line of sight propagation
Propagation of Radio waves:
Surface Wave:
A ground wave travels along the surface of the Earth (Thus the ground wave
is required to be vertically polarized-vertical electric field). As the wave travels it
induces energy currents into the Earth and thus looses energy as it travels. Due to
dissipation of energy into the Earth the surface wave suffers attenuation, which is a
function of Earth’s conductivity. The loss is compensated by the downward flow of
energy from upper layers due to diffraction. The wave front gradually tilts as it
propagates and finally the wave dies. Thus range depends on the power and
frequency with which the initial wave is transmitted.
Space Wave:
For frequencies in the range of 30 MHz ground waves get attenuated within
a few hundred feet distance. These waves do not get reflected even by the
Ionosphere. Hence the only way of transmission is by line of sight. The limitation
is the curvature of the Earth. Space wave comprises of two types. The direct wave
and the ground reflected wave. The problem with the later type is unless the
resultant of the direct wave and reflected wave is significant at the receiving end
the signal strength may not be of any use. The problem of shadow zone is
associated with space, antenna height and LOS reception.
Ionospheric Wave:
Due to ultra violet radiation the molecules in the atmosphere get ionized.
Since the density of molecules is high and radiation is low at lower heights the
ionization effect is not felt. But at distances of 50 Kms to 500 Kms above the
Earth’s surface this is considerable. This area of ionization is called ionosphere.
For waves of frequencies below 100 KHz the change in electron density
occurs over a distance relatively smaller than wavelength and the ionosphere will
act as a perfect reflector. Long distance propagation is possible due to multiple
reflections between Earth and Ionosphere. In case of waves of higher frequencies
the Ionosphere acts a bad conductor and as a refractive medium due to which the
wave gets refracted as it passes through the layers and eventually gets bent towards
the Earth. For certain angles of incidence the wage will not get reflected back but
passes through the layers. So a critical angle of incidence comes into effect. When
an electromagnetic wave gets trapped in the Earth’s atmosphere it tends travel
fairly large distances along the surface of the Earth and this phenomenon is termed
as duct propagation.
Maximum usable frequency:
This is the maximum frequency that can be reflected back for a given
distance of transmission using reflections from the atmosphere.
Skip Distance:
The minimum distance over the transmitted after going into the atmosphere
touches the Earth for the first time. Reception within the skip distance is not
possible while using sky waves.
Impedance matching:
The iron-cored transformer is used for matching impedances at the lower
frequencies. At higher frequencies air core transformers are used for impedance
matching. Another method used for impedance matching is the usage of four
terminal networks. The four terminal networks is composed of reactive elements
to avoid dissipation of the RF power and also it can be used over a narrow band of
frequencies thus resulting in increased efficiency of transmitted power. The
network is designed on an image basis to match the resistance part of the load.
Wave Guides:
Up to 1 GHz, the attenuation in polyethelene cables is mainly due to the
conductor material (i.e. copper losses). The attenuation varies as the square root of
the frequency. Beyond 1 Ghz, the dielectric losses also become appreciable and
vary as the frequency of operation at 10 Ghz. At still higher frequencies the
current tends to travel at the outer surface and loss is due to the core material.
Removing the core material can increase the efficiency of transmission. This gives
rise to the hallow pipe or the wave-guide.
Antennas:
An antenna is a structure – generally metallic and sometimes very complex –
designed to provide an efficient coupling between space and the output of a
transmitter or the input to a receiver. Like a transmission line, an antenna is a
device with distributed constants, so that current, voltage and impedance all vary
from point to the next one along it.
The antenna offered with the fixed station Transceiver is of ground plane type
having omni directional radiation pattern.
Antenna Gain and Effective Radiated Power:
Certain types antennas focus their radiation pattern in a specific direction, as
compared to an omni directional antenna.
Directive Gain:
Directive gain is defined as the ratio of the power density in a particular
direction of one antenna to the power density that would be radiated by an omni
directional antenna (isotropic antenna). The power density of both types of
antenna is measured at the same distance, and a comparative ratio is established.
1. The longer the antenna, the higher the directive gain.
2. Non-resonant antennas have higher directive gains than resonant antennas of
equal lengths.
Directivity and power gain:
The maximum directive gain is defined as the gain in the direction of one of
the major lobes of the radiation pattern. The maximum directive gain is also
referred as Directivity.
Another form of gain used in connection with antenna is power gain. Power
gain is a comparison of the output power of an antenna in a certain direction to that
of an isotropic antenna. The gain of an antenna is a power ratio comparison
between an omni directional & unidirectional radiator.
This ratio can be expressed as
A (dB) = 10log10 (p2/p1)
A (dB) = antenna gain in decibels
P1 = Power of unidirectional antenna
P2 = Power of reference antenna.
Field Intensity:
The field strength (field intensity) of an antenna’s radiation, at a given point
in space, is equal to the amount of voltage induced in a wire antenna 1m long,
located at that given point.
The field strength, or the induced voltage, is affected by a number of
conditions such as the time of day, atmospheric condition & distance.
The voltages induced in a receiving antenna are very small, generally in the
microvolt range. Field strength measurements are thus given in microvolt per
meter.
Antenna Resistance:
Radiation resistance is a hypothetical value, which, it replaced by an
equivalent resistor, would dissipate exactly the same amount of power that the
antenna would radiate.
Radiation Resistance:
Radiation resistance is the ratio of the power radiated by antenna to the
square of the current at the feed point.( P= I*I*R)ISQUARER
Bandwidth, Beam width, & Polarization:
Bandwidth, beam width & polarization are three important terms dealing
respectively with the operating frequency range of an antenna, the degree of
concentration of its radiation, and the space orientation of the radiated waves.
Bandwidth:
The term bandwidth refers to the range of frequencies over which the
antenna radiates effectively i.e. the antenna will perform satisfactorily through out
this range of frequencies.
Beam width:
The beam width of an antenna is the angular separation between the two half
-power points on the power density radiation pattern.
Polarization:
Polarization of an antenna refers to the direction in space of the E field
(electric vector) pattern of the electromagnetic wave radiated from an antenna.
Grounded Antennas:
If an antenna is close to the ground, the earth acts as a mirror and it becomes
a part of the radiating system. The ungrounded antenna with its image forms a
dipole array, but the bottom of the grounded antenna is joined to the top of the
image. The system acts as the antenna of double size.
The Marconi antenna has one important advantage over the ungrounded, or
Hertz, antenna. To produce any given radiation pattern it need be only half as
high. On the other hand since the ground here plays such an important role in
producing the required characteristics, the ground conductivity must be good.
Where it is too low, an artificial ground is used. The radiation pattern of Marconi
antenna depends on its height.
Ungrounded Antenna:
An image antenna is visualized to exist below the earth surface and is a true
mirror image of the actual antenna. Once the image has been established, the
resulting radiation may be considered as having come from the antenna and its
image, rather than from an antenna situated above a reflecting surface.
Horn Antenna:
There are two types of horn antennas present. They are basic horn and
special horn. When a wave-guide is terminated by a horn, the abrupt discontinuity
that existed is replaced by a gradual transformation.
UHF and Microwave Antennas:
Transmitting and receiving antenna designed for the UHF (0.3 – 3GHz) and
microwave (1-100GHz) regions tend to be directive.
Antennas with Parabolic Reflectors:
A practical reflector employing the properties of the parabola will be a three
dimensional surface, obtained by revolving the parabola about the axis. The
resulting geometric surface is the paraboloid, often called a parabolic reflector or
microwave dish.
2) ROLE OF COMMUNICATION (at VSP)
The communication plays an important role in the following things:
To transfer information (voice, video, data) from one place to another
place efficiently.
To avoid the delay in production.
To avoid time delay in communication.
For instantaneous transfer of information.
To get proper feedback.
For the effective coordination among various departments or sections.
3) TYPES OF COMMUNICATION :
Different types of communication systems are being used to meet the
internal and external communication needs. These are broadly classified as follow:
General-purpose communication systems.
Process communication systems.
Monitoring and signaling systems
It is obvious from the classification that every type of communication
system cannot be used in every type of environment. Communication systems are
chosen in each shop floor depending on the ambient noise, communication needs
etc.
A. General-purpose communication systems.
The following facilities are provided under category of general-purpose
communication systems:
3000 lines electronic exchange in plant.
2000 lines electronic exchange in town ship.
2500 lines electronic exchange of BSNL.
B. Process communication systems.
To facilitate coordination among operation & management activities of
production, maintenance and service departments, the following process
communication systems are provided:
Despatcher communication systems.
Loudspeaker intercom systems.
Loudspeaker broadcasting systems.
Loudspeaker conference communication systems.
Industrial public address system.
Hot line communication systems.
VHF communication systems.
C. Monitoring and signaling systems.
To facilitate and operate production activities remotely the following
Monitoring and signaling systems are provided:
Closed Circuit Television Systems (CCTV).
Central fire alarm signaling system.
Supervisory Control and Data Acquisition Systems (SCADA).
Shift change Announcement Siren system.
Briefly,
1. For the purpose of Intra shop communication needs ELECTRONIC
“Despatcher Communication Systems” are used.
2. In order to communicate in noisy environment and also to communicate
between any two stations having interconnectivity on selection basis, we use
“Loud Speaker Intercom Systems”.
3. For communicating general information to personnel on the shop floor
“Loud speaker broadcasting systems”. Are being used
4. For locating individuals and then communicating personally in noisy
environment, we prefer “Loud speaker conference communication systems”.
5. For the purpose of Communication by means of announcement and also
through hand sets in private mode in extremely noisy environments like that of
power plants, “Industrial public address and conference communication
system” are used.
6.Specified locations are connected permanently so that whenever one
subscriber lifts his telephone the other will immediately get a ring and
communication can be had with out any loss of time using “Hotline
communication systems”.
7. In order to supervise critical operating areas of major production units from
their concerned control pulpits, we prefer “ Closed Circuit Television Systems”.
8. For the simultaneous actuation of sirens to alert personnel of the affected
plant zones, we prefer “Central fire alarm signaling system”.
9.For closely monitoring the generation and distribution of energy
rationalization of the distribution based on the available energy, we prefer “
Supervisory Control and Data Acquisition System”.
10. For ensuring uniform and accurate shift timings throughout the plant, we
prefer “Shift change Announcement Siren System”.
11. For the purpose of talking to individuals while working at site or on move “
VHF Communication Systems” are used
1. Hand held VHF Walkie Talkies:
This system comprises of hand-held VHF mobiles (including a battery pack)
working on the respective battery frequency. Usually these walkie-talkies are in
the hands of the shift in-charges and some key operators, who have to be moving
regularly.
2. Mobile phones :
A VHF Base Station means a VHF Transceiver fixed on mobile equipment
like jeeps of CISF and fire fighting fleet etc working on the vehicles of the battery.
3. Base stations:
A VHF Base Station means a VHF Transceiver fixed in a metallic / wooden
enclosure along with an ‘AC’ to ‘DC’ power supply equipment and external
sockets for fist microphone and antenna connections.
The Base Station is to be fed with 230V 1-, AC power supply. This AC
will be converted into a DC voltage of 13.2v by the power supply cabinet inside
the base station of PRM 8020
1d.OBJECTIVE
To Study VHF Communication systems employed in Coke Ovens Batteries
of C&CCD department in VSP. The study starts with comparison of various types
of communication systems that can be used in battery applications. After this the
superior system i.e. VHF Communication is explained in detail. Of the various
models employed, the VHF Base Station with PRM 8020 Transceiver of Simoco
Telecommunications make, is taken up in this project. This involves the study of
circuit diagrams, the hardware aspects, programming screens and trouble shooting
techniques.
2
2. Coke ovens and VHF system:
There are a total of 3 battery complexes presently operational in VSP. Each
complex consists of a battery of 67 ovens and one CDCP (Coke Dry Cooling
Plant). For each battery approximately 80 to 85 Coke pushing’s are done every
day. These operations are carried out by Ovens’ machines in each battery. The
following persons are involved in operation for each pushing and they are
provided with VHF system.
a. Operations Shift In-charge
b. Pusher Car Operator
c. DE (Door Extractor) Car Operator.
d. Charging Car Operator
e. Loco Operator
f. CDCP Lifter Operator
g. CDCP Control Room Operator.
Since four of the above locations are moving machines, a wired
communication is not practically viable. The best option for a maintainable
communication system is to go for a fixed type VHF system in all the seven (7)
locations. The single phase AC power required for the VHF system operation is
drawn from the machine supply.
A VHF System consisting of a seven VHF base Stations is required for
working in each battery. For this purpose, all the stations are to be tuned onto a
common frequency. In the case of battery I and II, some of the Ovens’ machines
are common for operations. It means that these common Ovens’ machines can be
utilized either in Battery I or in Battery II ovens. Therefore, dual frequency VHF
base stations are provided for Battery I and II machines.
For non-conflicting operations, the three Batteries (including the respective
CDCP) will work on three independent frequencies.
The three frequencies allotted to the Batteries are:
1. 149.450 MHz – Battery – I Frequency
2. 149.550 MHz – Battery – II Frequency
3. 149.650 MHz – Battery – III Frequency
S. No. LocationBattery
Number
Fixed /
Moving
Frequency
Value Type
1. Shift In-
charge Room
I Fixed 149.450Mh
z
Single
2. Pusher Car 1 I Moving 149.450Mh Single
z
3. Pusher Car 2 I or II Moving 149.450Mh
z
149.550Mh
z
Dual
4. Pusher Car 3 II Moving 149.550Mh
z
Single
5. Charging Car
1
I Moving 149.450Mh
z
Single
6. Charging Car
2
I or II Moving 149.450Mh
z
149.550Mh
z
Dual
7. Charging Car
3
I or II Moving 149.450Mh
z
149.550Mh
z
Dual
8. Charging Car
4
II Moving 149.550Mh
z
Single
9. DE Car 1 I Moving 149.450Mh
z
Single
10. DE Car 2 I or II Moving 149.450Mh
z
149.550Mh
z
Dual
11. DE Car 3 II Moving 149.550Mh Single
z
12. Loco 1 I Moving 149.450Mh
z
Single
13. Loco 2 I or II Moving 149.450Mh
z
149.550Mh
z
Dual
14. Loco 3 II Moving 149.550Mh
z
Single
15. CDCP-I
Control Room
I Fixed 149.450Mh
z
Single
16. CDCP-II
Control Room
II Fixed 149.550Mh
z
Single
17. Lifter Cabin –
1 (CDCP-1)
I Fixed 149.450Mh
z
Single
18. Lifter Cabin –
2 (CDCP-1)
I Fixed 149.450Mh
z
Single
19. Lifter Cabin –
3 (CDCP-1)
I Fixed 149.450Mh
z
Single
20. Lifter Cabin –
4 (CDCP-1)
I Fixed 149.550Mh
z
Single
21. Lifter Cabin –
5 (CDCP-2)
II Fixed 149.550Mh
z
Single
22. Lifter Cabin –
6 (CDCP-2)
II Fixed 149.550Mh
z
Single
23. Lifter Cabin – II Fixed 149.550Mh Single
7 (CDCP-2) z
24. Lifter Cabin –
8 (CDCP-2)
II Fixed 149.550Mh
z
Single
25. Telecom Lab I, II and
III
Fixed 149.450Mh
z
149.550Mh
z
149.650Mh
z
Multi
26. Shift In-
charge Room
(Battery- 3)
III Fixed 149.650Mh
z
Single
27. Pusher Car 4 III Moving 149.650Mh
z
Single
28. Pusher Car 5 III Moving 149.650Mh
z
Single
29. Charging Car
5
III Moving 149.650Mh
z
Single
30. Changing Car
6
III Moving 149.650Mh
z
Single
31. DE Car 4 III Moving 149.650Mh
z
Single
32. DE Car 5 III Moving 149.650Mh
z
Single
33. Loco 4 III Moving 149.650Mh
z
Single
34. Loco 5 III Moving 149.650Mh
z
Single
35. CDCP III
Control Room
III Fixed 149.650Mh
z
Single
36. Lift Cabin 9
(CDCP III)
III Fixed 149.650Mh
z
Single
37. Lift Cabin 10
(CDCP III)
III Fixed 149.650Mh
z
Single
38. Lift Cabin 11
(CDCP III)
III Fixed 149.650Mh
z
Single
39. Lift Cabin 12
(CDCP III)
III Fixed 149.650Mh
z
Single
PRM 8020 General Information:
The PRM 8020 series is a mobile radio transceiver unit manufactured by
M/s Simoco Telecommunications Limited. These are under-dash mounted local
controlled simplex radios for vehicular applications. The transceiver utilizes
microcomputer to control a frequency synthesizer and also to perform the analog
signaling. To suit the site requirements i.e. changing the frequency, band, power
and other features is called customization. Customization of the microcomputer
control is done via an EEPROM. This programming of the EEPROM is done
through a field-programming unit (FPU). The FPU consists of the system software
required for operation of PRM 8020, which in turn is loaded on a personal
computer. For customization, the transceiver is connected through its microphone
socket to the external PC.
TYPICAL CONNECTION FOR PROGRAMMING A TRANSCEIVER:
PRM 8020 provides up to 64 channels & 8 additional buttons are provided
which can be programmed to accept the additional features. The front panel of the
transceiver utilizes liquid crystal display. (LCD).
2a.Blockdiagram:(material fig 23)
3
3.Construction: The transceiver consists of three printed circuit boards (PCB).
The PCB’s are double-sided epoxy fiberglass type. Surface mounted components /
devices are extensively used along with some conventional leaded components.
The three PCB’s are defined as
1.Front Panel Board.
2.Control Board.
3.Radio Board.
A chassis made of die-cast aluminum provides heat sinking for power
amplifier & regulating devices. The radio and control PCBs are attached to the
chassis and are shielded from each other. The radio PCB has a separate Zinc
shield, which is fitted on the components’ assembly side. Interconnection between
the radio and control PCBs is done via a flexible printed circuit (FPC) and the
socket fitted to the radio PCB. Another flexible printed circuit with the socket
fitted to the front panel PCB connects the control PCB to the front panel PCB. The
front Panel PCB is housed in a separate plastic moulding.
In the front panel, eight moulded plastic buttons are provided. The Liquid
crystal display (LCD) is protected by means of a plastic lens. The front panel PCB
is attached to the front panel moulding by fixing screws.
A chassis mounted BNC type socket at the rear side of main chassis
provides antenna connection to the unit.
Loud Speaker and DC power connection are provided by a 4-way connector
socket mounted on the control PCB. A microphone socket is available as two
parallel ports.
1. A. 15-way D type connector (on the rear of the chassis)
2. RJ45 type socket (accessible through an opening on the front panel)
3a. Technical Description:
1. Receiver:
The receiver uses super heterodyne principle with a first and second IF
frequencies of 21.4MHz and 455KHz respectively. (Double conversion super
heterodyne principle)
The front end of the receiver uses electronically tuned band pass fitters and a
radio frequencies amplifier ahead of a double balanced mixer. The frequency
conversion to the first IF of 21.4MHz occurs in this mixer with the local oscillator
injection from the receive voltage controlled oscillator (VCO). Monolithic crystal
filters at 21.4MHZ provide the first stage of adjacent channel rejection.
Amplification at 21.4MHz is provided before frequency conversion to the second
IF of 455KHz. The final stage of adjacent channel rejection is provided by a
ceramic filter.
The second conversion, IF limiter amplification and FM demodulation are
all processed in a single IC. The demodulated audio out of this IC is first low pass
filtered to remove residual 455KHz products and then further de-emphasis, is
provided. The mute gate is before the volume control adjustment, which is before
the audio power amplifier.
The demodulated output is also high pass filtered, amplified and detected.
Super heterodyne F.M. receiver: (fig 108 ken)
Fig gives the block diagram of a super heterodyne F.M. receiver. It is similar
to super heterodyne A.M. receiver. The main constituent stages of F.M. receives
are as follows:
(i) R.F. Amplifier or signal Frequency Amplifier: It serves the same
functions as in amplitude modulation super heterodyne receiver. Thus it serves (a)
to raise the signal level appreciable before the signal is fed to the mixer and (b) to
discriminate against the image signal. But in F.M. broadcast, the signal bandwidth
is large being 150 KHz as against 10KHz in A.M. broadcast. Hence the R.F.
amplifier must be designed to handle this large bandwidth.
(ii) Frequency Mixer: It performs the usual function of mixing or
heterodyning the signal frequency voltage and the local oscillator voltage to
produce the difference frequency voltage, which is the intermediate frequency
voltage. Since F.M. broadcast takes place either in the VHF band or UHF band,
signal transistor frequency converter is not used and hence a separate local
oscillator is used. The intermediate frequency used in F.M. receivers is higher than
that in A.M. receivers operating at short waves. This high intermediate frequency
helps in image rejection.
(iii) Local Oscillator: A separate local oscillator is always used. At high
frequencies, it is preferred to keep the local oscillator frequency smaller than the
signal frequency by an amount equal to the intermediate frequency.
(iv) I.F. Amplifier: A multistage I.F. amplifier is used to provide large gain.
Further this I.F. amplifier should be designed to have high overall bandwidth of the
order of 150KHz. Since the overall bandwidth decreases as the number of stages
in cascade increases, it is necessary to design individual stage to have
correspondingly higher bandwidth than the overall bandwidth desired.
(v) Limiter: The IF amplifier is followed by a limiter which limits the I.F.
voltage to a predetermined level and thus removes all amplified variations which
may be incidentally caused due to changes in the transmission path or by man
made static or natural static.
(vi) F.M. Detector: This extracts the original audio modulating frequency
voltage from the frequency modulated carrier voltage. A discriminator is used as
the F.M. detector.
(vii) Audio Amplifier: The output of the F.M. detector is fed to an audio
frequency small signal amplifier and one or more audio frequency large-signal
amplifiers. The o/p audio voltage is then feed to the loud speaker. Often two or
more loudspeakers are used, each reproducing a limited range of frequency.
Advantages of super heterodyne receiver:
The advantages of super heterodyne receiver make it the most suitable type for the
great majority of radio receiver applications; AM, FM, communications, single
side band and even radar receivers all use it, with only slight modification in
principle
Phase Discriminator:
Phase discriminator is also called as the center-tuned discriminator or the
Foster-Seelay discriminator. It is used as a FM demodulator. Its main function is
to change the frequency deviation of an incoming carrier into AF amplitude
variation. This conversion is done efficiently and linearly.
The circuit diagram of Phase Discriminator is as given above. The Foster
Seelay discriminator is derived from a balanced slope detector. It uses two slope
detectors connected back to back, to the opposite ends of a center-tapped
transformer, and hence fed 1800 out of phase. The presence of L3 ensures that the
voltages fed to the diodes vary linearly with the deviation of the input signal.
The primary and secondary voltages are related as given below:
1. Exactly 900 out of phase when input frequency is fc
2. Less than 900 out of phase when fin is higher than fc
3. More than 900 out of phase when fin is below fc
2.Transmitter:
The transmitter power amplifier amplifies the 20 mill watts level of the
VCO to achieve 25 watts final output. The amplifier design in broadband without
mechanical tuning. Power output is stabilized by the action of a feedback loop.
This power control loop circuit also protects the amplifier from excessive load
mismatch conditions and temperature rise. The output from the amplifier is
coupled to the antenna socket via the antenna change over switch and the harmonic
rejection low pass filter.
Power output can be set between 1 and 25 watts, with the option of
switching between to preset power levels.
Transmit audio processing begins with an active microphone containing a
transistor preamplifier. The microphone signal is filtered and amplified, in the
transceiver unit, ahead of an amplitude limiter stage. Following the limiter, the
signal is low pass filtered prior to modulating the transmit VCO.
3. Microprocessor Control:
A single chip 8-bit CMOS microprocessor forms the basis of the computer
control circuitry within this device is a masked program read only memory. The
program generates and detects selective call tone sequential signaling, as well as
the operational characteristics of the selcall system response. In addition, the
microprocessor programmes the synthesizer, updates the LCD display, controls the
receiver audio mute and transmit microphone mute, monitors the front panel
buttons, controls CTCSS and reverse tone burst signaling, programmes and reads
the electrically erasable memory.
The electrically erasable memory contains the user customizable
information, which includes features such as channel frequency, signaling system
requirement (tone set, code, system response etc). and transmit limit timer value.
The memory is programmed or read, via the microprocessor, from the microphone
socket interface.
The microprocessor operates from an external 12MHz clock controlled by a
crystal oscillator. The clock frequency in divided by an additional IC to provide a
clock signal of 1MHz for the CTCSS option.
A latch, between the microprocessor and several controlled functions of the
transceiver, provides a port expansion of the microphone and isolates the more
sensitive radio control interfaces from the microprocessor clock noise.
4. Synthesizer:
The frequency synthesizer provides the function of excitation for the transmitter
power amplifier, and the receiver first local oscillator. A signal phase locked loop
principle is used with synthesis at the required final frequency. The phase locked
loop comprises the transmit and receive VCOs, a prescaler/divider, programmable
divider and phase comparator, reference oscillator, and loop low pass filter. The
action of the loop is phase lock the VCO frequency to the stable reference
frequency, which is derived from a crystal oscillator.
The synthesizer is reprogrammed to a new frequency by a serial sequence of
data commands to the programmable divider IC, this data is latched in the IC. For
frequency modulation in transmit mode, both the transmit VCO and the synthesizer
reference oscillator have modulation applied.
Frequency Synthesized Signal Generator:
To understand the basic function of the frequency synthesizer, imagine that a
technician, wishing to reduce the frequency drift of a signal generators, decides to
set the frequency of the generator every few seconds by reacting to the counter &
adjusting the generator accordingly to the correct frequency. This is the human
equivalent of the phase-locked loop frequency synthesizer.
One very popular method of frequency synthesis is called the indirect
method or the phase- locked loop shown in fig. Four main components are
required the VCO or voltage controlled oscillator, the phase detector, the phase
reference & loop fitter.
The VCO is the source of the O/p frequency & has the ability to tuned
electronically, usually by applying a variable voltage. Some oscillators are
electronically tuned using a current, especially in the higher frequency, but for the
general discussion of a PLL Frequency synthesizer, the signal voltage will be
considered a voltage-controlled device.
The programmable divider is a logic element that divides the frequency of
the VCO by an integer that can be entered via programming switches a
microprocessor or other method.
The phase detector provides an analog O/p that is a function of the phase
angle between the two inputs, which in the case of frequency synthesizer is the
reference source & the o/p of the programmable divider.
The reference source is a very accurate & stable frequency source, which is
typically a quartz crystal oscillator. The accuracy of the entire synthesizer is
independent on the accuracy of the reference source. The crystal oscillator
operates in the region of 1 to 10 MHz and this frequency is divided down using
digital counters to provide the necessary clock & reference frequencies for the
synthesizer. The loop filter is an analog filter.(block diagram manual 31)
Fv = N*Fr
Fv = desired frequency of the VCO
N = integer entered into the programs divide
Fr = reference frequency.
The programmable divider divides the frequency of the VCO by N and the
O/p frequency of the programmable divider is Fv/N. The reference oscillator O/p is
also divided down by a programmable divider to produce the synthesizer reference
frequency Fr.
The signals of Fv/N and Fr are combined in a phase comparator, which
produces an O/p voltage proportional to the phase error between these two inputs.
The error signal is connected, via the loop filter circuit block, back to the voltage
control input of the VCO. The error signal causes the VCO frequency to be
modified so that no phase difference exists between the two-phase comparator
inputs. When this occurs the loop is said to be phase locked and Fv/N =Fr.
If the programmable divider value of N is increased by 1 to N+1, then for
the phase lock to occur, Fv*/N+1 = Fr, where Fv* is the new VCO frequency and
hence it can be shown that Fv*= Fv+Fr. Therefore, by setting Fr to equal the
channel spacing, it is possible to select a particular channel by choosing the
appropriate value for N.
When the synthesizer is used as the transmitter exciter, modulation must also
be applied. This is achieved using the two-point modulation technique. The VCO
is directly modulated but, because this signal will be seen as a phase error, which
the loop will attempt to correct, it is necessary to apply modulation to the reference
oscillator. The modulation polarity for the VCO and reference oscillator must be
the same.
Indirect Synthesizer with Microprocessor Control(fig ref notes,material31)
Frequency synthesizers are found mostly in all communication equipment.
The microprocessor is used in the communication system to facilitate the purpose
of remote control, as well as to enhance operational flexibility and convenience.
The availability of the frequency synthesizers, which avoided the need for manual
turning and calibration.
The functional diagram of communications receiver microprocessor control
is as given below (page 143 kennedy)
Functioning:
The microprocessor, after receiving its instructions from a remote control or along
the data bus from the manual controls, initiates an address sequence. The word or
words in this sequence are decoded are applied to a number of key points in the
receiver, which then generate the desired actions. One of the addresses is applied to
a set of data latches. These, in turn, select the appropriate AGC function, the
wanted IF band pass filter from among the six provided, and the appropriate audio
function. The address is also applied to the manual controls, where appropriate
voltages select the wanted channel, IF gain, form of frequency scanning and so on.
It is also applied to the liquid crystal displays, to ensure that the selected quantities
are correctly indicated for the operator. Similarly the data latches operate the
Synthesizer interface and the BFO interface on request by the microprocessor or
because of the manual settings adjusting their outputs to the desired values.
Microprocessor controls very significantly increase the versatility of a
communications receiver. This has many applications – such as switching between
two distant receivers for best output under fading conditions, complete remote
control of coast radio station from a central point. Further, complex search and
channel selection patterns can be stored in the microprocessor memory and used as
required with very simple initiation procedures. Test routines can be stored and
simply used as required.
Phase Locked Loop:
A Phase Locked Loop (PLL) is a feedback loop with a phase detector, a low
pass filter, an amplifier and a voltage – controlled oscillator (VCO). Rather than
feeding back a voltage, the PLL feeds back a frequency and compares it with the
incoming frequency. This allows VCO to lock on to the incoming frequency.
The Phase-Locked Loop Principle has been used in application such as FM
Stereo decoders, motor speed controls, tracking filters, frequency synthesized
transistors and receivers, local oscillator frequencies in TV and in FM tuners etc.
Phase detector:
A phase detector is a mixer optimized for use with equal input frequencies. It is
called a phase detector (or phase comparator) because the amount of DC voltage
depends on the phase angle between the input signals. As the phase angle
changes, so does the DC voltage.
Voltage – Controlled Oscillator:
A voltage – controlled oscillator is a source of a periodic signal whose
frequency may be determined by a voltage applied to the VCO from an external
device.
Functioning of PLL:
The phase detector, or comparator compares the I/p frequency f in with the
feedback frequency fout. The o/p of the phase detector is proportional to the Phase
difference between fin and fout. The o/p voltage is a dc voltage and it is referred as
the error voltage. The o/p of the Phase detector is applied to the low-pass filter,
which removes the high frequency noise and produces a dc level. This dc level is
in turn is the I/p to the voltage – controlled oscillator (VCO). The o/p frequency of
the VCO is directly proportional to the I/p dc level. The VCO frequency is
adjusted until it is equal to input frequencies. The PLL goes through three states:
free running, capture, and phase lock.
Before the I/p is applied, the PLL is in the free-running state. Once the I/p
frequency is applied, the VCO frequency starts to change and the Phase-locked
loop is said to be in capture mode. When phase locked, the loop tracks any change
in the I/p frequency through its respective action.
EEPROM
EEPROM (Electrically Erasable Programmable Read Only Memory)
is a semiconductor memory, which is electrically erasable and hence inherently
possesses on-board programming and erasing facility. The microprocessor and
EEPROM are the only devices on the serial data bus, which can both send and
receive data. The EEPROM is a 512-byte device configured as 256/16,but as it is
communicating with an 8-bit microprocessor, the control program treats it as an 8-
bit array.
When programming the EEPROM, as the initial configuration of the
equipment, the following steps occur:
1.The EEPROM is sent a write enable command and the enable line turns high.
2.Nine bits of data are locked in and the enable line turns low.
3.Next, the 28 bits of data to be written to the EEPROM and the program
command are clocked into the device. The data out line is load during
programming and high when programming is completed. Typically the
programming takes 5 to 10 ms.
4.When finished, a write disable command is issued to the device.
5.Reading of data in the EEPROM is accomplished by setting the enable line
high and then clocking in the read command and address. The data of that
location is clocked out and enable line turned to low.
6.When reading a byte, only 8 bits of data are clocked out. When reading 16bits,
the whole 16bits are clocked out.
7.When reading channel data, the read command, address and then 48 bits of
data are clocked out. When changing channel and an invalid channel selected,
only the read command, address and two bits of data are clocked out. If the
channel data is valid, the 48 bits of data are clocked out.
EEPROM, is hence, referred in applications where the permanent
programs are frequently needed to be updated on board.
Signaling:
Selective call tone frequencies are in the microprocessor. A digital to analog
converter provides a low distortion encode signal. Receiver demodulated selcall is
band pass filtered before a zero-crossing detector. The circuit produces impulses
at twice the frequency of the demodulated selcall tones and provides a waveform
suitable for processing directly by the microprocessor.
The CTCSS encode & decode function is performed in a single integrated
circuit. The IC is controlled by the microprocessor the encoder / decoder IC also
provides a high pass fitter when in receive mode to remove the demodulated tone
ahead of the audio power amplifier.
A reverse tone burst feature is provided. A 180 degree phase shift is
available in encode directly out of the encoder/decoder IC.
The selective call signaling is achieved by means of a software control
program operating in the main control microprocessor for both encode and decode
functions.
Power Supply & Reset: Three regulated supply voltage are required for operation
of the transceiver circuitry. These are +9v, +5v & +23v. The +9v & +5v regulated
supplies are derived from integrated circuit and the +23v supply is generated by a
multivibrator circuit and a voltage multiplier. The high voltage supply is used to
provide a wider control voltage range for the varicap diodes used in the VCO's and
receiver front and filters.
A permanent +5v trickle supply is provided for the microprocessor. This
enables stored information to be maintained during short duration power failures,
and the last programmed state to be retained when the transceiver is switched off.
To ensure reliable operation of the microprocessor, an interrupt and reset
circuit is provided. The circuit detects power failure and induces the
microprocessor to prepare for a reset. The timing between interrupt and reset is
carefully controlled to ensure that the microprocessor is enabled and disabled in a
predictable manner during supply failure and restoration. The reset operation is
also rate limited and prevents enabling of the processor before the supply voltage
has stabilized sufficiently.
The interrupt and reset operation is designed to detect total loss of primary
power, or supply voltage reduction below the regulator limit of the +9v regulator.
Switched Power Supply:
Switched power system and switched mode regulators are used for their high
efficiency intensive development has taken place over the last few years to produce
power supplies of maximum efficiency and small size & weight. Many of these
circuits are developed from the basic inverter. An inverter is a device that converts
dc to ac.
In the circuit this is achieved by the switches S1 & S2 which alternately
reverse the dc connection to the transformer primary. The transformer has to be
center – tapped on one half cycle current flows through the top half of the primary
winding and on the other, when the switches change, the current flows in the
opposite direction through the lower half of the primary. The result is that A.C
will be produced at the secondary. The switches are usually special purpose
transistors or thrusters driven by some form of square wave or pulse oscillator.
Another method is to have feed back windings on the primary so that the inverter
transistors form a self-oscillating circuit. The frequency of the switching signal,
especially if the inverter is used as part of a regulator, is typically in the range.
By following an inverter with a rectifier circuit of filter a converter, that is
D.C to A.C is created if a feedback loop is them added that senses the D.C O/p,
compares it with a reference level, feeds a signal that can be modify the switching
time of the transistor, a type of switched regulator results show in fig (a) this
circuit uses a principle called primary switching.
Controls and Display:
In PRM 8020 version of the front panel, the visual display indications are
provided by a liquid crystal display. A single integrated circuit is used to drive the
display information to be displayed in programmed and latched into the driver IC
by the microprocessor.
The momentary acting push-button switches are connected directly to a set
of dedicated inputs on the microprocessor.
4
4. Technical Specifications:
General operation: Single or Two-frequency simplex
Modulation: Frequency modulation (Phase)
Power requirements: 13.8V dc negative earth
Current consumption:
Stand by: Less than 350 mA
Full Audio: Less than 700 mA
Transmit (25 watts): Less than 6.5 A
Frequency Bands:
Switching Bandwidth: Complete frequency band coverage without returning
(1dB).
Number of channels: 64
Channel spacing: 12.5/20/25/30KHz
Frequency Stability: 10/5/2.5ppm
Operating temperature: -300 to + 600c
Transmitter:
Power output: 1.5, 6,10,15, of 25 watts
Duty cycle: 1 minute transmit – 4 minute receive (at 25 w)
Spurious Emissions: Less than 0.25uw (100 KHz to 1GHz )
FM Residual Noise: Better than 40dB
Audio frequency distortion: Less than 3% (at 1KHz for 60% deviation).
Audio frequency Response: within + 1dB to –3dB of 6db/octave Pre-emphasis
curve over 300 to 3000Hz (2.55KHz for
12.5KHzchannel spacing)
Transmitter Rise time: Less than 40m sec.
Receiver:
Sensitivity: Better than 0.31uV pd for 12 dB sinad
Adjacent Channel Selectivity: Better than 75dB at 25KHz channel spacing.
Better than 65 dB at 12.5KHz channel spacing.
2-signal EIA method
Intermodulation Rejection: Better than 75dB
3-signal EIA method
Spurious Response Rejection: Better than 80 dB
Single signal method for 12dB sinad response
Blocking: Better than 90 dB
Audio Frequency Response: within + 1dB to –3dB of 6db/octave de-emphasis
characteristics from 300 to 3000Hz (2.55KHz for
12.5KHz channel spacing)
Mute Delay: Less than 40 ms at 20dB sinad.
Audio Output: Better than 4Watts at 5%distortion into 4 ohm.
5
5.Additonal features of base station:
Description
Feature Summary Benefit
Two versions
available
The PRM 8020/8010 versions. Have
variable signaling capability and
operator selectable scanning. It can
provide 6a channels.
Meets different
user
requirements.
Industrial
design
Designed by Philips corporate
Industrial design for case of use.
Features smooth rounded design for
safety. Styling matches vehicle facial
mouldings.
Easy to use- safe
to operate
attractive
appearance.
Flexibility Professionally engineering for
versatility features wideband RF and
flexible software package.
Will meet
majority of user
needs.
Automated
manufacturing
Manufactured with the latest SMD
Technology on common PRM 80 flow
line
Improved
Delivery, lower
cost and high
reliability over a
wide range of
product variants.
OPERATIONAL FACILITIES
Transmit inhibit Prohibits mobile transmission
when a carrier signal is
present on the channel.
Allows the
conversation to
proceed without
interruptions.
Transmit
Limit timer
Limits of length transmission
by automatically inhibiting the
Transmitter after a
predetermined period
Does not allow the
radio channel to be
inadvertently or
deliberately locked
up.
High /low Power
selection
Radio channels can be
programmed with either high
or low transmit power levels
Enables the user to
reduce RF power
when required.
TRANSCEIVER ELECTRICAL PACKAGE
Complete
frequency band
coverage with
narrow band
receiver
Tracking narrow band (6MHz)
front end with electronic
tuning provides complete
frequency band coverage
(1dB).
Ideal for large
systems users with
many scattered
channels. Tracking
front end provides
high performance.
Transceiver Economic design with limited Simplified spares
Design number of specific
components
holding.
Wide operating
temperature
-300C to +600C Reliable operation in
extreme
environments
High receiver
sensitivity
0.31uv at 12dB sinned Extended range of
operation
Audio output 4 watts at 5% distortion High quality audio
OPERATOR CONTROL
Liquid crystal
display
Large backlit LCD with
display of channel, selective
call and operational
information.
High visibility even in
direct sunlight.
Operator control
push buttons
Large size push buttons for
control of main functions.
Easy to see, find and
operate.
Volume control Volume control is rotary type Easy adjustment by
user.
Variable squelch
option
Variable receiver mute
threshold provided by a
Allows operator
adjustment of receiver
control concentric with
Receiver volume control.
muting level in high /
low reception signal
conditions or
interference. For
maximum range and
intelligibility.
SCANNING AND CTCSS
Scanning Up to 10 channels can be
scanned for a signal.
User can monitor a
number of channels.
Priority Channel
scan
Priority channel scan is
available to enable the radio
to scan for a busy channel
whilst still monitoring the
normally used priority
channel.
User can listen to other
channels and still
monitor his channel.
CTCSS Continuous Tone Controlled
Squelch System
incorporating EIA tones
Provides protection
from unwanted calls
on shared radio
channels
CTCSS frequency
variable per
CTCSS frequencies are
programmable per channel.
Enables the user to
access different bases
channel by change of channel
switch.
DTMF signaling DTMF microphones encode
option.
Works into PABX
systems or SPCX
PROGRAMMING FACILITIES
Group call Radio provides for normal
group tone sequence or free
from tone sequence.
Allows base operators
to contact a number of
mobiles
simultaneously
Alarm function Activated by normal alarm
switch or external emergency
alarm switch. Mobile can be
programmed to send normal
alarm sequence or it can go
into deducted emergency
mode.
Provides a facility for
user to alert base of an
emergency or it can be
used as a priority
speech request.
Message
acknowledge
Auto acknowledges and
delayed call acknowledges
are provided.
Mobile responds
automatically to
confirm receipt of a
call.
CUSTOMISING
Customization Broadband RF
characteristics. Separate
Receiver and Transmitter
VCO's.
Mobile is ideally
suited to users
requiring fast
customization
Onsite: Non-Volatile
memory so no back-up
battery required. No
need to remove covers.
6
6.Programming of base station:
7
7. Maintenance & Trouble Shooting :
The circuiting being fully solid state and free from moving parts needs
minimum maintenance. However, the following points should be checked from
time to time.
1. Output voltage setting should be 13.2Volts without load. On load (Max 6A) the
voltage can drop to maximum 0.3 Volts. If the voltage falls, beyond this then
check R35R4 and also voltages on IC pin nos. 5 & 6 which should be within
1.5 to 1.6 volts. For adjusting the output voltage at 13.2 volts use R6 only. If
the output voltage is not up to the level, then the pilot lamp gets dim when the
transmitter is switched on.
2. If mains hum is experienced, the likely reason could be drop in voltage output
of the power supply due to drop in main supply voltage or drift in voltage
setting. In case persistent low mains voltage is the reason, top changing of the
transformer secondary and checks as in point 1 and the problem of hum can be
eliminated. Another reason for hum could be due to poor earth connection in
the 3-pin supply socket. Ensure a good earth connection through the earth pin
in the mains socket.
3. For detailed checks on the power supply card, refer to the voltage data and the
circuit diagram provided.
4. If transmission is not possible check the antenna cable to make sure that it is not
short circuited or broken any where along the length of the cable. Check that
the microphone cable is properly connected and no wires are broken.
5. If carrier is transmitted without any modulation, the probable fault could be in
the microphone. Check that the microphone capsule connecting wires are not
broken.
6. If the reception is intermittent, adjust the squelch pre set through the hole
provided in the front panel of the set. Turn the pre-set potentiometer anti clock
wise to desensitize the squelch setting.
7. In case battery is kept connected, ensure that the battery terminals are clean in
order that good electrical contact is obtained.
8. In case a severe fault is suspected, do not attempt to open the LTS set especially
during the guarantee period. Consult us by providing as much observed fault
details as possible to enable us to guide you.
T1 3515 138 10000 Transformer
R1 2315 321 14038 wire wound Resistor 0.3E, 5w
R2 2315 321 14038 wire wound resistor 0.3E, 5w
R3 2315 321 14018 wire wound resistor 0.1E, 5w
R4 2315 321 14028 wire wound resistor 0.2E, 5w
R5 2315 411 07103 Pot meter 10ktypeA 6H
R7 2315 211 03102 Resistor CR 25 1k + 5%
R8 2315 321 32251 wire wound resistor
3515 138 10010 P.C. Board 250E, 10w
C1 2215 108 12502 A1. E1. Cap 5000 uF, 50V
C2 2215 108 14101 A1. E1. Cap 100uf, 25V
C3 3515 344 21104 Polyester cap 0.14F+10%, 100V
C4 3515 344 21104 Polyester cap 0.14F+10%, 100V
D1 3515 030 01630 Fall wave rectifier 5RB1510R/Per115P
D2 3515 030 01530 Fall wave rectifier 5RB1510/Per115N
TS1 9315 975 10229 Transistor 2N 2219A/PBD13>
TS2 9315 976 10305 Transistor 2N 3055
TS3 9315 976 10305 Transistor 2N 3055
TS4 9315 976 10305 Transistor 2N 3055
TS5 9315 976 10122 Transistor BC 148 Bor Equiv
TS6 9315 977 10112 Transistor BC 158 B
TC1 3515 030 03085 I.C. CA 3085A
F1 3515 200 10110 Fuse 1Amp.
F2 3515 200 10120 Fuse 6Amp.
SK 3515 020 09810 Socket Assy.
VOLTAGE LEVELS
Typical Values DC Volts
Power Supply PCB Emitter Base Collector
TS1 (2N 2219A) 14.5 (NL) 15.0 (NL) 28.5 (NL)
15.5 (NL) 16.0 (NL) 22.0 (OL)
TS2 (2N 3055) 14.0 14.5 (NL) 28.5 (NL)
15.5 (NL) 22.0 (OL)
TS3 (2N 3055) 13.75 14.0 28.5 (NL)
22.0 (OL)
TS4 (2N 3055) 13.75 14.0 28.5 (NL)
22.0 (OL)
TS5 (BC 148 B) 13.2 13.5 13.5
TS6 (BC 158 B) 13.6 (NL) 13.5 13.2
15.3 (OL)
IC(CA 3085 A) Pin No. 1 & 8 15.0 (NL)
16.0 (OL)
Pin No. 2& 3 28.5 (NL)
22.0 (OL)
Pin No. 4 0
Pin No. 5& 6 1.5 to 1.6
Pin No.7 13.6 (NL)
13.3 (OL)
Test points TP1 0
TP2 28.5 (NL)
22.0 (OL)
TP3 14.5 (NL)
15.5 (OL)
TP4 13.2
TP5 13.2
TP6 13.2
TP7 13.5
NL – No Load Voltage OL = on Load Voltage
.
8
8.Suggested applications of vhf systems:
Some of the suggested applications of VHF systems are given below:
1.Wireless Video Link
2.Wireless LAN
1. Wireless Video Link:
The Wireless Video Link consists the following equipments:
1.Camera
2.Microphone & Audio amplifier
3.Antenna (both transmitting and receiving antennas)
4. Monitor
Here in this application the camera is placed at remote places where
manual operation is not possible. The camera is aimed at the scene so that the
optical image can be focused on the target plate of the pick up tube and the light
variations are converted to corresponding electrical signals. The microphone
converts the sound waves to corresponding electrical variations for the audio
signals. These audio signals are further amplified and transmitted along with the
video signals using transmitting antenna. These signals received at the receiving
antenna are amplified and then fed to a monitor.
9
9.Conclusion:
The VHF systems are widely used because of the following advantages.
1.No cables required:
VHF communication does not require any cables for communication. On the other
hand the telephones require different types of cables twisted pairs, coaxial cables
and optical fibers.
2.User friendly:
The VHF sets are very easy to operate. By simply pressing a switch one can
communicate with another in different location.
3.Critical applications:
Since walkie-talkies are designed to operate under critical applications such as
MIL (military) applications, the VHF sets, which are the extension of the walkie-
talkies, can also be used for critical applications.
4.User programmable:
The VHF sets can be programmed very easily. The amount of power to be
transmitted can be adjusted to low, medium or high.
5.Congestion:
The VHF sets are free of congestion because they operate over a wide range of
frequencies (149-174 KHz) where as in telephones depending upon the number of
lines and the number of subscribers, the congestion may arise.
6.Easy to install:
As cables are not required, the VHF systems can be installed very easily with out
loss of time where as the telephone requires installation of cables, towers etc.
7.No external disturbances:
In telephones the cables are installed overhead or they may laid under the ground.
In case of overhead cables there may be disturbances due to external voltages,
thunders, lightenings, magnetic fields created due to H.T wires where as in under
ground cables, moisture may affect the signal. These problems do not occur in case
of VHF communications.
8.Vehicular application:
As these sets do not require cables, they can be carried out easily on vehicles
where as the telephones which require cables and hence they cannot be carried on
vehicles.
