HF preamplifier with threshold needed

[neazoi]

Hello I need to see if there is any HF preamplifier circuit, that has the next special function.
The preamplifier should be able to amplify signals only above a certain level. Prefferably, this level should be variable, user selected.
Signals below this level should be left not amplified, or otherwise cut off.

This is not the same as a squelch circuit (in audio). A squelch circuit would amplify both low and high level signals, but only when enabled by the prescence of a high level signal.

 

[BigBoss]

You have to use Received Signal Strength Indicator Circuit (RSSI) to cut-off the amplification below certain level.
You can even build a RSSI circuit for acceptable accuracy. Seek internet for "logarithmic amplifiers or RSSI circuits".