When you look at a broadband amp such as the antenna amp on your TV do you understand that the amp is amplifying channel 1 and channel 10 and channel 100 and all in between all at once? If so it should not be to difficult to accept one amp can amplify AF and RF so I will simply show the circuit and offer a brief, hopefully logical theory of operation.
First the basis for circuit analysis. First step define DC biasing. More often than not getting the DC established is the biggest job the rest falls into place. Now the circuit in question.
What do we know about transistors? One thing is they amplify current. A small current through the base produces a large collector current. The amount of current gain is the transistor Beta factor. If ß is 100 and we apply 1 micro amp through the base we get 100 micro amp out the collector. Be aware the RF transformer is in series with the base current and look at the signal on the transformer.
Does that make since?
Just imagine they placed a switch in the bias circuit which is switching at an RF rate. HEY! That might be why they call them switching diodes.
The transistor selection could effect this circuit a lot. I have some with a ß of 1000. Um 1 micro amp to 1 milli amp would be a giant leap in signal?!?
EDIT: As base current increases collector voltage decreases reducing the diode bias. In case you did not see that.That would be the feedback or reflex function.
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