[Elecraft] AGC Design of the K3

[Bill W4ZV]

Shane White wrote:
> 
> I noticed a remedy for the following problem on the K3 enhancement list -
> 
> Hardware AGC threshold change
> Some users prefer tuning the band with a wide filter bandwidth selected
> (for example, using a 2.7 or 2.8 kHz SSB filter in CW mode rather than a
> 500 Hz or narrower filter). Strong off-frequency signals (above about
> S9+5) that are inside the crystal filter passband can then activate the
> hardware AGC circuit, reducing the level of desired signals. 
> 
> Shouldn't a radio's AGC only use signals within the selected final IF
> passband width to control gain?
> 

No because the DSP stage doesn't have enough dynamic range to handle the
full 140 dB range of possible input signals.  There are two AGCs in the K3,
Orion, etc...analog ahead of the DSP stage and digital within the DSP.  The
analog AGC ahead of the DSP is needed to protect the ADC from overload and
the digital can then handle about 100 dB internally.

73,  Bill  W4ZV
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