Re: AGC circuit to try?

Jerry Gaffke
 

Any an attenuator used up front at the uBitx antenna port 
will be dealing with a whole world's worth of RF, 
so any non-linearity in the attenuator could create IMD products 
due to a strong local AM or FM or TV or hairdryer signal.

The situation gets slightly better after the 30mhz low pass filter at L1,2,3,4
Much better after the 45mhz crystal filter.
Much much better after the 12mhz filter.

Though as Tim has pointed out, the 12mhz filter might
be especially sensitive to variations in impedance.

Pick your poison.

Jerry


On Tue, Apr 10, 2018 at 10:36 am, Jerry Gaffke wrote:
The half-life of the charge carriers in a PIN diode is only around a microsecond,
so won't work at all at audio frequencies, must be prior to D5 pin 3.

Most of the AGC schemes we see here suppress the audio after the audio pre-amp.
And they work well enough.
But we should get more dynamic range (be able to receive strong signals) if the AGC
attenuator is somewhere between C50 and the antenna port.

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