Chokes can be classified into
- Audio Frequency chokes which function at the power and audio frequency and
- Radio Frequency chokes which function at high frequencies.
What is a Choke ?
Chokes can be classified into
Comparison of Optical Fibres and Metallic Wires
| Optical Fibre | Metallic Wire |
| Not a lightning hazard as it is non conducting | Can attract and transmit lightning |
| Lighter in weight | Heavier in weight |
| Not affected by Interference | Affected by interference |
| High data bandwidth | Lower data bandwidth |
| Lower data loss | Data loss is more |
| Faster data transmission | Relatively slower data transmission |
| Unauthorised tapping of data is difficult | Easier to tap data without authorization. |
| Difficult to terminate | Easier to terminate |
| High initial cost | Lower initial cost |
| Less affected by chemicals and pollution | More prone to effects of pollution |
| No risk of sparking. Hence, can be used in petroleum and chemical industries. | Risk of sparking and fire. Hence, cannot be used in hazardous environments. |
Terminating Resistors-An Overview
Terminating resistors are used in communication cables to prevent reflection of the transmitted signal. The reflected signal can cause interference which may affect data transmission. Hence, to prevent this resistances are connected in parallel.
The value of the impedance will match the wave impedance of the line. Thus a communication line with an impedance of 120 ohms will have a 120 ohm resistor connected across it. Short cables can function without terminating resistors.
What is a Band Stop Filter?
A Band Stop Filter is a filter which blocks a set of frequencies in a specific band and permits frequencies above and below that range to pass through.
Functionally, the Band Stop filter does the opposite of the Band Pass Filter.
The series LC circuit is connected in parallel. At the resonant frequency of the LC circuit, the reactance is minimum. Thus a specific frequency is shorted across the input and prevented from reaching the output.
The Band Stop Filter can be made by connecting a Low Pass Filter and a High Pass Filter in parallel.
What is a Band Pass Filter?
A Band pass filter combines the characteristics of the High Pass and Low Pass Filters.
The Band pass Filter, as the name suggests, allows only signals of a particular band or range of frequencies to pass through. All other signals are blocked or shorted. 
Band pass Filters can be made by connecting a high pass filter in series to a low pass filter or vice versa.
A Band pass filter can be made by connecting an inductor in parallel to filter the low frequency components which lie below the desired frequency. Another inductor in series will then block the high frequency components which lie above the desired frequency.
Likewise, the Band pass filter can also be made using capacitors as in the second figure. Here, the first capacitor filters the high frequency components and the second capacitor in series blocks the low frequency components.
What is a High Pass Filter ?
A High Pass Filter is a filter which permits high frequency signals to pass through and blocks only low frequency signals. The high pass filter has a relatively simple construction. The filter can be constructed by either providing a low impedance path to high frequency signals from the input to the output or by providing a low impedance path to low frequency
If a capacitor is connected in series between the input and the output, it will provide low impedance to high frequency signals and high impedance to low frequency signals. High frequency signals alone will be able to pass the capacitor.
Alternatively, if an inductor is connected in parallel to the input, it will offer low impedance to low frequency signals which will get shorted across the input. High frequency signals will alone reach the output.
What are Low Pass Filters ?
A Low pass filter is a filter which permits only low frequency signals to pass through. High frequency signals are blocked or shorted across the input. The low pass filter offers low impedance to low frequencies and high impedance to high frequencies.
There are two ways of constructing a Low Pass Filter.
The first method is to connect an inductor in series to the output. The reactance of the inductor is so chosen that it offers high reactance to high frequency signals. Thus, high frequency voltages are blocked. At low frequency, the reactance is low and thus low frequency signals are allowed to pass.
Another method is to connect a capacitor in parallel to the input. The capacitor provides low reactance to high frequency signals which are shorted across the input. The low frequency signals see a high reactance in the capacitor and they alone reach the output. The series resistance serves to limit the current.
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