[Elecraft] New K3 Firmware: Pileup-inspired AGC changes

[Joe Subich, W4TV]

> #  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-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Wes Stewart
> Sent: Thursday, February 26, 2009 10:32 AM
> To: elecraft at mailman.qth.net; Jim Brown
> Subject: Re: [Elecraft] New K3 Firmware: Pileup-inspired AGC changes
> 
> 
> 
> 
> --- On Wed, 2/25/09, Jim Brown <jim at 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 at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>