Factors that affect ADSL

Attenuation

Attenuation is the loss of signal strength over distance during transmission. It increases with line distance, transmission power, Temperature and frequency. ADSL is a technology that hardly suffers from attenuation when the distance is increased from DSLAM to subscriber.

Bridge taps

Bridge tap is an unterminated extra length of with that connects to the local loop. Usually left over when subscriber is connected to existing pair of copper wires, and the original subscriber at the end of the pair is disconnected leaving and open-leak at the end of the wire.

When the ADSL signal is sent across the wire and it reflects through the bridges tap. The signal travels to open leak side and then bounces it back. This reflected signal is then mixed with the original signal and confuses the modem. Therefore bridge tap must be removed before install ADSL.

Cross Talk

Crosstalk is a disturbance in a wire caused by the electric or magnetic fields of other signals in other wire pairs of the same cable bundle. There are two types Crosstalk types. They are known as,

Near End Crosstalk (NEXT) is interference between two pairs in a cable measured at the same end of the cable as the transmitter.
Far end crosstalk (FEXT) is interference between two pairs of a cable measured at the other end of the cable from the transmitter.

Split pairs

Split pairs occur when one conductor is in a pair is become separated from the other conductor. They result in noise and cross talk. This will harm line condition and the quality of ADSL service.

Noise

The total power in a transmission line is made up of the signal and noise. Nose is always present but it should always be kept as low as possible in relationship to the signal. Factor that introduced noise are,

Radio and television

Transmitter

Power distribution system

Electrical Machinery

Mechanical vibrators

Dual-tone multi-frequency signaling (DTMF)

Dual-tone multi-frequency signaling (DTMF) is used for telecommunication signaling over analog telephone lines in the voice-frequency band between telephone handsets and other communications devices and the switching center.

When we consider dialing numbers in the telephone now days commonly uses DTMF. Using DTMF (dual tone multi frequency) when we press a key on our phone, it generates two tones of specific frequencies. Then the signal is encoded as a pair of sinusoidal (sine wave) tones from the table below which are mixed with each other. The mixed frequency is traveled to the exchange.

DTMF

Advantages of DTMF compare to Rotary Dialing 

The main advantage is easy to access the phone when we are taking a call. But using rotary dialing hard to make a call.

When we are taking a call, in rotary dialing we have to rotate the numbers. Rotary dial pulses cannot pass through a central exchange. It is time consuming. Normally it takes an average of about 1.5 seconds per digit, or 15 seconds for dialing a 10-digit number. But DTMF tones can pass through a central exchange. It is recognized by the register at the central exchange. A DTMF tone must be present for a minimum of 40 ms. Between two consecutive digits, a pause of 60 ms is required. Total time needed for transmission of one digit is about 100 ms. Compare to rotary dialing it takes very much low of time .It is more efficient than rotary dialing.

Usage of Microwave frequency & Wave length

Usage of Microwave frequency & Wave length

• Microwaves are electromagnetic waves with wavelengths ranging from 1 m down to 1 mm, or equivalently, with frequencies between 0.3 GHz and 300 GHz.
• The microwave range includes ultra-high frequency (UHF) (0.3–3 GHz), super high frequency (SHF) (3–30 GHz), and extremely high frequency (EHF) (30–300 GHz) signals.
• Wireless LAN protocols, such as Bluetooth and the IEEE 802.11 specifications, also use microwaves in the 2.4 GHz ISM band, although 802.11a uses ISM band and U-NII frequencies in the 5 GHz range.
• Cable TV and Internet access on coaxial cable as well as broadcast television use some of the lower microwave frequencies. Some mobile phone networks, like GSM, also use the lower microwave frequencies.
• Microwave radio is used in broadcasting and telecommunication transmissions because, due to their short wavelength, highly directive antennas are smaller and therefore more practical than they would be at longer wavelengths (lower frequencies). There is also more bandwidth in the microwave spectrum than in the rest of the radio spectrum; the usable bandwidth below 300 MHz is less than 300 MHz while many GHz can be used above 300 MHz.
• Most satellite communications systems operate in the C, X, Ka, or Ku Bands of the microwave spectrum. These frequencies allow large bandwidth while avoiding the crowded UHF frequencies and staying below the atmospheric absorption of EHF frequencies

Micro wave frequency ra