T2,T3,T4,T6,T7 Telecom

Connectors-

Two most common connectors used for professional audio are 3 pin XLR and 1/4 phone connectors.

RCA Connectors-

A round,press on connector used for audio and video connections.

F connectors- used for television and antenna applications.

N connectors- used by  cable TV industry.N means Navy.

C connectors- Similar to N connector. However they are Bayonet locking.

BNC Connector-( Bayonet Neil Conelment connector)

RF connector used for terminating coaxial cable.

Used in video and RF applications to 2 GHz.

TNC connector-

Threaded version of BNC connector 

Used in cellular telephone RF antenna connections.

Waveguide Tees-

Waveguide Tees are Waveguide junctions.

1. E type T junction 

2. H type T junction. 

Attenuator -

Used to Control the amount of power transferred between the  points on a transmission line by absorbing or reflecting some of Microwave power.

Directional Coupler-

It is four port component in which two transmission lines are employed in such way that output at port of transmission line depend on the propogation in other.

Modulation-

Modulation is the process in which amplitude, Frequency or phase of a high frequency wave called carrier is changed in accordance with instantaneous value of low frequency wave, called modulating signal.

Type of Analog Modulation-

1. Amplitude Modulation 

2. Angle Modulation ( frequency modulation and phase Modulation) 

Modulation index-

K= Em/Ec 

It is a number lying between 0 and 1

Digital Modulation Techniques-

1) Digital Amplitude Modulation or Ampitude Shift Keying ( ASK)

2) Frequency Shift Keying ( FSK)

3) Phase Shift Keying ( PSK)

Earth Electrodes-

There  are three types of earth electrodes. 

1) Plate type

2) Rod or pipe

3) Strip type 

Chemical Treatment of Soil-

Artificial reduction of Earthing resistance by treatment of soil with salt or similar compounds is generally not recommended except as last resort to improve specific resistivity.

Chemical used include Sodium chloride,Calcium chloride.Magnisium sulphate,copper sulphate.

Decibel -

Decibel is one tenth of bel (B), I.e 1B= 10dB

Although Decibel  measurement are always relative to reference level,if the numerical value of that reference is exactly stated ,then the decibel measurement is called absolute measurement.

dBm indicates power measurement relative to  1 milliwatt, 

0 dBm means no change from 1mW.

Thus 0 dBm is the power level corresponding to a power of exactly 1 mW.

3 dBm means 3 dB greater than 0 dBm.

Absolute measurement of Power-

dBm or dBmW

dB(1mW) - Power measurement relative to 1 milliwatt.

X dBm = X dBW + 30

dBW

dB(1 W) - Similar to dBm but the reference level is 1 Watt.

0 dBW = + 30 dBm

-30 dBW = 0 dBm

Cable Fault Locator-

Cable fault locator are of two types.

1. Pulse Echo Method

2. Time domain Reflectometry 

Transmission Measuring Sets ( TMS)-

Specially designed for maintenance of Telecommunication lines in telephone exchanges & on the field.

TMS is used for following measurements.

1. Signal Levels 

2. Insertion Losses

3. Transmission losses 

4. Return Losses

Insertion loss is the loss of signal power resulting from Insertion of a device in a transmission loss.

Measurements used in OFC

Visual Fault Locator-

It is also called Laser fault locator.

It uses 650 nm or 635 nm visible laser that emits a bright beam of Laser light into a fibre,allowing the user to visually detect a fibre fault upto 5 km.

It is used for following.

1. To locate breaks 

2. To locate macro bends

3. To locate faults in connectors.

4. To find end to end identification.

Optical Power Meter-

It is used to determine how much attenuation ( loss) the light emitted from a light source suffers,while it travels through a given length of fibre.

Optical Time Domain Reflectometer ( OTDR) -

It is a key instrument used in field of fibre optics communication for testing the integrity and performance of fibre optics cable.It works on the principle of sending a series of optical pulses into fibre and analyzing the reflected light to evaluate fibre's characteristics.

OTDR measures the time it takes for the back scattered light to return and intensity of the returned light.

This device analyzes the returning light to create a trace, a geographical representation of fibres performance.

Following can be measured with OTDR.

1. Fibre Attenuation Characteristics 

2. Insertion Loss ( connector)

3. Splice loss.

4. End to end loss measurement.

5. Break point.

Micro bending in OFC

1. Microbending losses occur when an optical fibre bends on a small scale,causing light to scatter and reducing transmission quality.

2. This is loss induced by physical stress on the fibre.

3. The loss which exists when an optical fibre undergoes bending is called bending losses.

4. It affects both,attenuation and loss.

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