Low Noise Amplifiers (LNAs) are designed to amplify signals such that they rise above the noise floor in radio systems. An increase in signal level relative to noise makes it easier to process the signal.
This is the primary use case of an LNA. However, it is not the only application. For instance, an LNA can be used in transmitter systems or in general, systems where signal amplification is required.
HOW SHOULD I CONNECT MY LNA?
The RFin or RF input terminal of the LNA should always be connected to the source of the signal. In receiver systems, RFin should be connected to the antenna. The unmarked terminal at the other end, should be connected to the RF input of the radio receiver.
In transmitter systems, RFin should be connected to the output of the transmitter. The unmarked terminal at the other end should be connected to the antenna.
What about transceivers or devices that both transmit and receive signals from the same port (such as Wi-Fi access points and Helium hotspots)?
A LNA cannot be connected between the antenna and the hotspot in such situations as it only amplifies signals that are present at the RFin terminal. The LNA does not amplify signals in both directions!
In fact, if you use it in a transceiver with a single Tx/Rx port, you run the risk of damaging both the transceiver and the LNA.
The only exception to this is if you are able to control the transceiver such that it only operates as a receiver or a transmitter. Typically, this is the case when you use a software-defined radio (SDR).
An SDR can be configured as a receive-only device in which case you can connect the LNA as you would with a receiver.
Now what if your transceiver has separate ports for transmit and receive?
In this situation you can use an LNA on each port. Note that the RFin always connects to the source of the signal. In the case of the transmitter, it is connected to the Tx port. For the receiver, it is connected to the antenna.
