At 07:10 PM 2/2/2010 -0500, you wrote: >Brian, > >That is an illusion - yes the K3 gets more quiet (on noise) if the AGC >Threshold is reduced. >BUT what that indicates is that the AGC is being activated by the noise >and the K3 is reducing the gain due to AGC action. >The lowest AGC Threshold that is usable for any given level of >atmospheric noise is the threshold setting just higher than the setting >which begins to reduce the noise. In other words, listen to a spot on >the band where there are no signals, then start at the highest Threshold >setting of 008. >Reduce the value of the AGC Threshold until you sense that the noise >level starts to go down - then move the Threshold up to the next level. > >That setting will produce the most usable sensitivity for that band, >that antenna, and at that particular point in time (atmospheric noise >levels do change with time). If the resulting noise level is >bothersome, then take other steps to reduce that response - Preamp off, >ATT ON, and reduce the RF Gain (in that order) until you can just barely >hear the noise. That will result in the most sensitive setting for the >receiver. >Remember (as Jim Brown just posted) - that atmospheric noise is just >another 'signal' to the receiver that is to be amplified (it is coming >in on the antenna port). One must condition the receiver to place that >noise level at (or just above) your threshold of perception to reduce >your fatigue level when listening to any band. That is what the preamp, >attenuator, and RF Gain controls are for.
Hi, I am not an Elecraft owner ... yet ... However I have built (homebrewed) many receivers over the years ... and building a good AGC system is one of the hardest parts (biggest challenge in modern parlance). One of the things I learned after many years is how to make the AGC sensitive to noise. Most of the receivers I built and commercial ones I have used basically relate the AGC level exclusively to received signal. However in designing the AGC detector time constants I found it very useful to have receiver gain controlled by noise level to some degree. As background noise goes up ... receiver gain goes down to a degree ... and as the background gets quieter gain should go up a little. I never did get it just right ... and the general front end attenuator and RF gain control always got used a lot hi hi. I find the topic very interesting .... and I find it very encouraging the effort put into AGC design in the K3. Jim, VE3CI ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
