[Elecraft] RE: Difference between "real" filters (FL1 thru FL4) andDSPfilters (SF1 thru SF4)

[Ron D'Eau Claire]

Steve, W2MY/5 wrote:

The DSP is audio.  Its got a sharper cutoff but can be affected by the AGC
which is also audio.  The crystals filters FL1 -FL4 are IF and closer to the
front end and cut interference before the AGC.

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The K2 AGC is not audio AGC. It's derived from RF in a separate I.F. strip
dedicated to producing an AGC voltage based on the strength of the signal at
the I.F. and the AGC voltage controls the gain of the I.F. amplifier. The
AGC circuits are on the control board. NE602 mixer U1 converts the I.F.
signal to about 150 kHz. That way any BFO signal at 4.9 MHz can't get into
the AGC system. The output of the NE602 is rectified to produce the DC AGC
voltage that operates the "S" meter and which controls the gain of the
MC1350 I.F. amplifier (U12) on the RF board. 

Ron AC7AC