For those who can gather information from graphs, take a look at the AGC behavior Jack Smith has plotted. The information is at http://www.cliftonlaboratories.com/elecraft_k3_agc_and_s-meter.htm#AGC_SLP_and_AGC_THR.
73, Don W3FPR Don Wilhelm 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. > > After a bit of experimenting, you may come to the point where you have > achieved a compromise set of AGC Threshold and Slope setting that work > well in all but the most demanding situations. Leave them set at that > point and control the receiver response with the normal controls of > preamp, ATT, and RF Gain. For those digging for signals beneath the > noise level (yes, some ops have very good ears for that), they will have > to suffer with hearing some of the noise as well - just how much is an > individual decision. > > Again, as Jim Brown pointed out - noise arriving from the antenna is > just another signal source - some signals will be above that noise level > and others will be below it. Normally we can only copy signals that are > above the noise level, so why do some insist on setting "all controls to > the right" and having the receiver amplify the noise as well as the > signals - it is all in the quantity called "(signal + noise) to noise > ratio". > > The only way to further reduce noise is to use noise reduction > techniques which search through the signal plus noise to find something > that appears to be coherent and amplify it. That is what the K3 NR > algorithms do. How well it works depends on the type of noise present > at the time, and the K3 offers several settings to handle the differing > situations - do expect distortion with the more aggressive settings, but > if they are able to dig a signal out of the noise for us, perhaps we can > put up with the distortion to complete the contact. This is for use in > extreme situations, and not for normal use when we want more casual copy. > > 73, > Don W3FPR > > ______________________________________________________________ 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
