Re: Fwd: K3 Wide AGC threshold

Posted by Bill W4ZV on Nov 19, 2010; 9:50pm
URL: http://elecraft.85.s1.nabble.com/K3-Wide-AGC-threshold-tp5755595p5756731.html

Bob Henderson-2 wrote

The hardware AGC appears to be set at a level which precludes effective
utilisation of the 100dB+ DR of the DSP system.

Hi Bob...spoken like a former Orion user!  You're absolutely correct...but it's actually much better than it was originally.  Why?  I have no clue.

73,  Bill

Hardware AGC threshold change (HAGC Mod Kit)

http://www.elecraft.com/K3/k3_app_notes.htm  (scroll nearly to the bottom)

SMD HAGCMDKT instructions

Both through hole and SMD parts are included. Users can install either set of parts.

        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.

This modification raises the hardware AGC threshold from about S9+5 to about S9+25 to +30. The new threshold still protects the DSP's analog-to-digital converter, while providing better receive performance when wider crystal filters are used. This is not as significant an issue when using narrow CW filters (500 Hz and below).