The defensive hardware AGC is hardware AGC because you can see the entire circuit for this defensive AGC in analog components. It cannot be turned off. It is an AGC that in all circumstances would be better if you didn't need to use it, though this is clearly not possible in some circumstances. This is only one of various reasons for using the narrowest roofing filter that fits the mode and usage.
I could call hardware AGC simple-*ssed AGC, because it is, and it has only one purpose: don't overdrive the d*mned analog to digital converter (ADC). Hardware AGC seems more polite. ADC-defensive is more specific. DSP AGC is entirely done in algorithm in the number soup bit bucket. The degradation of NR performance occurs when the ambient noise level is allowed to hit the ADC at a high level, so that both the noise and desired signals are at the same level going into the ADC, with the defensive hardware AGC acting as the leveling device. The follow-on digital algorithms then have to accept as fact that the noise and the desired signal are now the same level. Perhaps with an ADC with another 30 or 40 db range, and similar increases in non-military cost processors are available, a defensive hardware AGC will not be needed. The manual solution to the quandary of the prior paragraph is to turn off PRE, perhaps turn on ATT, and perhaps reduce the RF gain pot as well until the ambient noise is only moderate at the K3 output. As clear as this might seem to some, attempts to correctly relate a "roaring noisy" K3 to PRE/ATT/RFgain settings for a band have often not been understood. PRE/ATT/RFgain are not dynamic adjustments, they don't vary in millisecond time ranges as found in hardware AGC. They vary at most at hand-twiddle speeds as they are manual. When the PRE/ATT/RFgain have been turned down so that ambient noise is in the LOW range at the ADC, then following digital algorithms have true information to work with, that has not been compressed by the hardware AGC. The DSP's "AGC" can do the stuff that can't be done with simple circuits. >From emails it is clear that proper manual reduction of PRE/ATT/RFgain to suit band and conditions is not catching on in a significant customer slice. My suggestion is to take these users at face value, that they want the setting of PRE/ATT/RFgain done automatically for best performance. If someone insists on calling that AGC, then there would be *THREE* AGC's. Hardware ADC-defensive AGC, digital level management in DSP algorithms, and a third, crawl-speed RF string management AGC. I'm thinking that the DSP can tell the difference between noise and discrete signal. It therefore can over a period of time (a second or two, or five or ten?) determine the best setting of PRE/ATT/RFgain and slowly engage the preamp, attenuator and set the resting gain of the post filter IF ampl based on that determination, rather than manual input. This latter automatic mode for RF string management could be engaged by reducing RFgain to minimum. To get out of it the user could advance the RFgain. At the point matching the automatic setting, the manual control would re-engage. The PRE/ATT settings would be left as is, because those would probably be correct. But they would follow the buttons if depressed. 73, Guy. On Fri, Jul 9, 2010 at 11:16 PM, Wes Stewart <[email protected]> wrote: > I'm sorry, but you can't have it both ways. > > "RF" (i-f) gain as implemented in the K3 operates on the post-filter (8 > MHz) i-f amplifier. The control voltage is derived at least two (perhaps > three) ways. > ______________________________________________________________ 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
