LNAs are used to increase the dB level of the overall RF spectrum, thus also increasing the noise. Normally, a filter would be applied before the LNA to reduce spurious signals. This is a LNA I bought from AliExpress (link), it does not work with Bias Tee, you need to power it using the pads on the board.
Watch out! Cheap LNAs like this one can and would add noise to your spectrum, don't cheap out on these, buy a good one instead.
I did some measurement on this cheap one, you can find them below:
These type of filters are used on RX circuits and only allows a small portion of the RF spectrum to "pass" through. In other words, they block signals on other frequencies that could interfere with the signal you are trying to receive (if a signal is too strong it could block or even damage your receiver).
This filtering increase the SNR (Signal to Noise Ratio) thus increasing the sensitivity of the receiver. This kind of filters is mandatory if you operate near a FM station and such.
Since I'm into radiosonde, I bought a 403s BPF (link) to install in my RX station. These are the measurements:
I'm also into LoRa and Meshtastic, so I have a transceiver for this band, and I needed a filter to increase my SNR which was very low, barely sufficient to receive messages via Meshtastic. So I bought this 868 BPF and these are the measurements:
Band Stop Filters are used to exclude a portion of the spectrum that contains very strong signals, for example the commercial FM radio stations band (88-108 MHz). In my area there are some strong FM station signals that interfere with the lower portion of the spectrum (27 MHz and such), so I also bought this FM BSF.
