> # I'm seeing 5 to 6 dB of increase in meter reading between > no modulation and modulation peaks. I guess I'm old fashioned > but I thought that the AM carrier strength should set the AGC > level.
It seems to me that this is exactly what one would expect. AM PEP = 4 x carrier (e.g. 6 dB). If an S-meter did not respond to peaks but rather responded to the "no modulation" signal level, it would be completely useless for CW or SSB. 73, ... Joe, W4TV > -----Original Message----- > From: elecraft-boun...@mailman.qth.net > [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Wes Stewart > Sent: Thursday, February 26, 2009 10:32 AM > To: elecraft@mailman.qth.net; Jim Brown > Subject: Re: [Elecraft] New K3 Firmware: Pileup-inspired AGC changes > > > > > --- On Wed, 2/25/09, Jim Brown <j...@audiosystemsgroup.com> wrote: > > > > > Someone just posted that they had trouble in pileups during the > > contest last weekend, but the radio worked better when they turned > > on the > > attenuator and turned down the RF gain. DUH! I learned > > that in 1957 -- > > but younger operators never learned it, since modern radios > > depend so > > heavily on AGC. > > Nothing personal Jim, but your post is a handy one to add to. > > I've been licensed for over 50 years so I've been through all > of the turn off the AVC (dating myself) and ride the rf gain > control business. > > But I must say that having to turn off the AGC and ride the > rf gain control in a modern whiz-bang super-duper > multi-kilobuck radio seems oxymoronic to me. Why should I > have to ride the gain? I thought all of this DSP stuff was > supposed to be smarter than I am. Shouldn’t the radio be > smart enough to know when a signal is so strong that the > attenuator needs to be inserted to "protect" the DSP or the > second mixer, for example? > > Besides the K3 AGC appears to never be "off" despite what the > display reports. For example while listening to a strong AM > broadcast station, if I reduce the RF Gain* with the AGC on > so that the S-meter stops peaking# and adjust the audio gain > for comfortable listening and then turn the ACG off, the > signal practically disappears. If the AGC was truly off then > there shouldn't be any change. Adjusting the RF Gain higher > to bring back the signal level will also result in the > S-meter following the signal peaks. > > Running this experiment also seems to demonstrate a problem > with the gain distribution in this radio. If I reduce the RF > Gain to the point that the S-meter is just beginning to be > affected, there is a distinct reduction in the SNR. It's > quite disconcerting to have a S9+50 dB, interference-free > signal that sounds noisy. > > Comparing to my TS870 with the same signal, I can decrease > the gain (increase the S–meter reading) by at least 20 dB > without noticing any reduction in SNR. > > * RF Gain seems to be a misnomer; unless I'm mistaken > (always a possibility) there isn't a gain-controlled RF > amplifier in the radio. The only hardware that is obviously > gain-controlled is the second stage in the first i-f amplifier. > > # I'm seeing 5 to 6 dB of increase in meter reading between > no modulation and modulation peaks. I guess I'm old fashioned > but I thought that the AM carrier strength should set the AGC > level. This peak-reading AGC may also be a contributor to > the distorted audio that has been widely reported. > > Wes Stewart, N7WS > > > > > ______________________________________________________________ > 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 > ______________________________________________________________ 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
