How can I decide the amplifier size ??

I’ve heard many times this question and I don’t have a straightforward answer, I’m sorry.?There are many factors that must be taken into account before doing the calculations on this. Finally the results of the calculation will tell the VSAT owner the size of amplifier needed to run the satellite link efficiently and effectively.?

Generally, satellite amplifiers are not measured in physical sizes. They are always measured in output power mostly watts (W).?Even the manufacturer's standard of measurement can be doubtful, some of them measure the amplifier output as Power(sat), which means the power required to saturate the signal. A saturated signal is not usable, and an amplifier measured in Power(sat) does not represent the practical maximum output power. A more accurate measurement is called P1dB.?

What is P1dB?

An amplifier usually provides a constant gain over a specific frequency range. If we represent the?Input power Vs Output power?of an amplifier on a graph, we get a straight line (Linear Relationship) i.e 'output power = input power + Gain' - so if the gain of an amplifier is 5 dB, then a 1 dBm input signal will result in a 6 dBm output signal. As the input power level increases, there comes a point where the output power of the amplifier no longer increases by the gain value so we called it the amplifier output power starts to saturate.?

The?1 dB compression point (P1dB)?is the output power level at which the gain decreases 1 dB from its constant value. Once an amplifier reaches its P1dB it goes into compression and becomes a non-linear device, producing distortion, harmonics, and intermodulation products. Amplifiers should always be operated below the compression point. P1dB is one of the most important specifications for power amplifiers, as it is up to this point that we consider an amplifier to operate linearly.?

In this scenario an amplifier is rated as say 50 watts?the idea is well almost all 50 watts can be used without distortion to the RF signal.?

Although the measurement of power is important it is just as important to know the frequency range of the amplifier.?

The following factors must be taken into account when we calculate the RF power of the amplifier.?

• Size of the Earth Station Antenna
• Size of the VSAT Antenna
• ?The satellite carrier bandwidth
• ?The signal strength of the satellite at the VSAT location
• ?Rainfall at both ends of the satellite link

The final calculation is performed by using the link budget formula, In most cases, the engineers in the satellite operation center will do the calculation of the link budget, nowadays most software-based systems also can do it accurately ex: Integrasys Beam budget, etc.?Finally, we can have an idea about how much power is needed in good weather conditions, and how much power extra power we need in bad weather to keep things safe.

Thank you.?