This circuit is from American documentation from the 70s. This configuration appears in this section obtained from other sources. The signal is sinusoidal determined in amplitude by D1 and D2.
Avago Technologies (www.avago.com) suggests the circuit in Figure 9 for amplifying signals of...
We found this circuit in a 1986 publication. However, as it is based entirely on 555 integrated...
This circuit can be used to listen for SSB signals on receivers that do not have the built-in...