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Four Essential LNB Parameters

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A low noise block (LNB) is a vitally important component for the majority of satellite ground stations. However, many engineers and managers don’t know the key information about them which can lead to system performance issues that everyone wants to avoid. Therefore, this blog provides the essential information on four LNB parameters.

LNBs are used on satellite ground station phased arrays and Figure 1 shows a typical block diagram. The LNB is normally connected between the phased array input and the system modem. As such, LNBs are an important part of a satellite phased array ground station. They are also used in dish antenna systems.

Figure 1. Simplified block diagram of a LNB showing the main functions.

Essential #1: Noise Figure

 

The noise figure of the LNB is one of the most important parameters of a LNB. This is because noise figure sets the receive sensitivity of the whole system. Many people will be familiar with the G/T requirement of a satellite ground station, but they may not realize that noise figure of the LNA is a major factor that determines the “T” part of the G/T calculation. Typical noise figure of the LNB is 0.6 to 0.9dB but depends upon operating frequency and can be higher or lower. Lower noise figure translates into higher G/T which is absolutely key to satellite ground station performance.

Essential #2: Gain

 

Along with noise figure, the gain of the LNB is a crucial performance parameter. This is because the gain of the LNB must increase the level of the satellite signal so that it can properly interface with the system modem. In other words, without the LNB required gain, the signal level will be too low to meet the minimum threshold required in the modem. The typical acceptable LNB gain is in the range of 50-70dB with 60dB a common requirement.

Essential #3: Output Compression Point

 

Most LNB units have a specification for gain compression point. Up to the gain compression point, the LNB output power versus input power curve must be linear. However, as the input power increases, a point is reached where the output power is no longer linear. This point is called the gain compression, or 1dB compression point. Most systems require a gain compression point of +10dBm to +17dBm.

Essential #4: IF Frequency Range

 

LNB modules are frequency down converters. As such, they will convert a down link signal to a lower frequency such as L and/or S-band. For instance, a Ku-Band LNB may operate from 11.7-12.2GHz as the satellite down link frequency, but the IF frequency band out of the LNB may be 0.950-1.45GHz. The IF frequency must be properly specified to match the modem so the system will perform properly.

Conclusions

 

An LNB will typically have 10-20 or more specifications that must be met. This blog presents four of the most critical parameters. If you have questions about LNBs or want to know how MPT can help you with your LNB needs, then feel free to call us at +1-951-252-6336 or by email at info@mptcorp.com.