We use electrical signals and electromagnetic waves to transmit and receive data. An efficient transmission of data with no or minimum losses is a fundamental requirement of any data transmission system. Whenever we talk about signal losses or signal strength, the term Attenuation comes up. But what is Attenuation? How it impacts the signal transmission? How do we measure it? What is attenuation in copper wires and fiber optic cables? We will explore the world of Attenuation in this guide and get the answers to all these questions.
What is Attenuation?
In simple terms, Attenuation is the loss of an electrical parameter of a signal (or an electromagnetic wave) such as voltage, current or power during its transmission. The amount of attenuation is usually the ratio of the electrical parameter at the output to the same parameter at input under specific conditions.
As the signal travels along the cable (or a transmission line), it gradually gets weakened due to attenuation. One of the main reasons for this is the impedance of the transmission line. Higher the impedance, greater the attenuation.
We usually represent Attenuation in decibels (dB) (more common) or Neper (N) (less frequent).
Attenuation in Signal Transmission
Irrespective of the type of medium, attenuation is persistent in all wired and wireless modes of transmission. For example, the strength of the signal will become less in your television’s cable, if the distance increases. Similarly, you will notice a drop in the Wi-Fi signal quality as you move farther away from the router.
Here are some of the cables and transmission media where there is attenuation.
- Co-axial Copper Cables
- Fiber Optic Cables
- Wireless Networks (Bluetooth, Wi-Fi, LTE, Cellular, etc.)
- Radio Signals (FM, AM)
- Satellite Communication
An important point here is that copper wires use regular electrical signals for transmitting data while optical fibers use light. Hence, copper cables are more susceptible to attenuation due to several factors (physical, mechanical, temperature, other near-by signals etc.) than fiber cables.
In case fiber, there is attenuation but not due to electrical interference or other electrical related reasons but due to physical, geometry of optical fibers, isolation etc. Hence, we can see plenty of fiber optical cables for long distance and high-speed networking as they usually have low attenuation rates.
We listed some main reasons for attenuation here. You can observe these reasons in a typical computer network that uses copper wires (co-axial or twisted pair).
- Impedance: The main reason for attenuation is the impedance of the cable. A cable with high impedance will usually have high attenuation rates and hence more signal loss. We usually indicate the cable quality on how low is its attenuation (lower the better).
- Interference/Noise: Another main reason for signal loss is due to interference from surrounding electrical signals. If cables have poor isolation, then other electrical and radio signals can easily affect its transmission. You get noise from surrounding electrical currents, leakages, etc.
- Physical: Apart from these, other factors such as temperature, obstructions (walls and barriers), improper cable/wire installations etc. can distort the signal.
- Wire Diameter: A wire with small diameter will usually suffer from greater attenuation than wires with relatively large diameter as small diameter cables have high impedance.
- Range/Length: The length of the cable is also a major contributor to signal loss. If the cable length is high or if the range of wireless network is long, then the signal loses its strength.
How to Measure Attenuation?
Measuring attenuation accurately is very important especially in high frequency RF (radio frequency) and microwave communication. For instance, with proper attenuation numbers in hand, designer of a RADAR System can easily estimate the amount of power a transmitter can transmit to an antenna.
There are several ways to accurately measure the attenuation of a communication system. Some of them are:
- Power Ratio Method
- Voltage Ratio Method
- Audio Frequency (AF) Substitution Method
- Intermediate Frequency (IF) Substitution Method
- Radio Frequency (RF) Substitution Method
From the previous section it is clear that we measure attenuation using decibels (dB). If PIN is the input power and POUT is the output power of a transmission line, then we can define attenuation in decibels (dB) as:
Power Attenuation AP (dB) = 10 log10 | PIN / POUT |
We can also define these powers as signal power at the transmitter end (PT) or source power (PS) and signal power at the receiver end (PR) or destination power (PD). Then the formula becomes:
Power Attenuation AP (dB) = 10 log10 | PT / PR |
Power Attenuation AP (dB) = 10 log10 | PS / PD |
Apart from power, we can also use input and output voltages to express attenuation. If VIN is the input voltage (or VS is the source voltage or VT is the transmitter voltage) and VOUT is the output voltage (or VD is the destination voltage or VR is the receiver voltage), then voltage attenuation is:
Voltage Attenuation AV (dB) = 20 log10 | VIN / VOUT |
Attenuation AV (dB) = 20 log10 | VS / VD |
Voltage Attenuation AV (dB) = 20 log10 | VT / VR |
Attenuation vs Amplification
If attenuation indicates signal loss, amplification is quite opposite to it. Amplification is the process of increasing/boosting the signal strength.
This is one of the main methods to prevent (or reduce the effect of) attenuation. When we are adjusting the volume knob of a radio player, we are actually settings its amplification but not its attenuation.
A Repeater is a type of amplification device that we often use with long distance cable communication. It consists of an amplifier circuit that takes a slightly weak input signal and boosts its signal strength. You can find multiple repeaters in cable TV transmission systems.
Attenuators
There will be some situations where we deliberately introduce attenuation into the transmission line. We do this to reduce or suppress the magnitude of unwanted voltage and currents. An attenuator is a system component that is designed to intentionally produce attenuation between the input and output terminals without affecting the impedance.
Most attenuators are pure resistive circuits. So, it doesn’t introduce any phase shift and all the frequencies will have a same degree of attenuation.
The term for attenuators with fixed level of attenuation is Pads. We generally use variable attenuators in radio communication systems. Here is a small list of some commonly used attenuators:
- T Type Attenuators (Symmetrical and Asymmetrical)
- π Type Attenuators (Symmetrical and Asymmetrical)
- Symmetric Lattice Attenuator
- Asymmetric L Type Attenuator
- Balanced Attenuator
- Variable Attenuator
Conclusion
Irrespective of the type of communication system, be it wired or wireless, all network systems have attenuation. It indicates the loss of electrical signal’s strength due to several factors (type of cable, impedance of the cable, interference, noise, range or distance etc.). We can measure attenuation in decibels (dB) to accurately indicate the amount of power loss in the transmission line.
