I believe I've written about this before, at least to a few, but perhaps it bears repeating. I have done a side-by-side comparison of my K3 with another K3 when "RF" (actually IF) gain was reduced with the AGC on.
With my radio, tuned to a S9+50 dB BC station, even a slight decrease in gain was met by a large *decrease* in SNR. On the other this wasn't the case. IMHO, this results from the wide differences in the volts v. dB characteristic of the gain-controlled hardware, i.e. the FET/diode post crystal filter amplifier, from radio to radio. This is why one guy can write, "SNR is improved when I reduce RF Gain" and another can say, "SNR goes to pot when I reduce RF Gain." Both can be correct, depending on their hardware. It's not new knowledge that we want to delay the application of AGC to early stages in the radio so as to maintain SNR. But in this radio, one size of delay doesn't fit all. The RF gain "calibration" is an attempt to fix in firmware what is essentially a hardware problem and Lyle has done an excellent job doing this. If I understand correctly, (always a dubious proposition) he measures the gain v. volts of the FET amplifier and applies this new found correction to the gain control partitioning. This has made a remarkable difference in my radio, which must be a real outlier. Still, and this is conjecture, I have this nagging concern that there might be some latency in the process and under highly dynamic conditions, it "doesn't keep up." Wes N7WS --- On Thu, 12/17/09, Ignacy <n...@arrl.net> wrote: > 2. Gain distribution under RF gain. RF gain under AGC does > not reduce noise > as much as with AGC off. The reduction with AGC on seems to > affect the first > stages first. So for a large decrease of RF gain the noise > reduction is not > as strong. Try listening to the same station with AGC off > and AGC on while > adjusting RF Gain. On the same note, the audio sounds > beautiful on strong > stations with large AGC hold but there is lots of noise > when the station > goes off. > > 3. AF distortions as documented by UR5LAM in > http://ur5lam.jimdo.com/elecraft-k3-mod-s-page/ > These may fixed with the new DSP board. Partially as UR5LAM > also applied > fixes to mixers and IF amp. found a few other fixes > necessary. > > The simplest fixes IMHO would be to extend the range of AGC > THR, and then > make RF gain behave similarly with AGC on and off. I > noticed a large > improvement after RF calib. For (3), a separate EQ setting > per mode would > help (if not already done). > > The noise is an issue important if K3 is marketed to > everyone. Like most in > this group, I find K3 highly superior to other radios in > contesting and > DX'ing. > > Ignacy, NO9E > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
