Joe, Can you elaborate your reasons for this suggestion. I had come to believe that the best situation is to place attenuation before the first mixer to give the greatest amount of dynamic range (headroom).
Yes, I agree that the AGC Threshold could be raised in the K3 and would be beneficial. I have felt the default of 005 was too low. 73, Don W3FPR Joe Subich, W4TV wrote: > Perhaps one should get the ambient well down in the ADC operating > range but killing gain (adding loss) before the first mixer and > the roofing filter is not the way to do it. If you want to > better align the dynamic range of the receiver (or specifically > the ADC) to conditions, the attenuation should come in the > IF - preferably divided between the first IF and 2nd IF. > > However, there would still be no apparent reason that the K3 > should not be capable of sustaining an AGC threshold at least > 10 db higher than currently set with AGC THR = 008 whether > that be reached with preamp on, preamp off or attenuator on. > > 73, > > ... Joe, W4TV > > > > >> -----Original Message----- >> From: elecraft-boun...@mailman.qth.net >> [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Guy >> Olinger K2AV >> Sent: Monday, February 08, 2010 1:49 PM >> To: nospam.li...@subich.com >> Cc: elecraft@mailman.qth.net >> Subject: Re: [Elecraft] K3 DSP AGC Question >> >> >> It may be a dance, but hopefully careful intelligent musing >> over the matter is convincing people that they should get the >> ambient well down in the analog-to-digital converter (ADC) >> operating range. If they do, a -99 threshold is a -109 >> threshold, and further backing off RF gain can make it a -119 >> or -129 threshold as far as the ADC is concerned, and >> headroom is being used for what headroom should be used for. >> >> One thing for sure, there has not been a good-enough >> presentation of what is going on, and people really don't >> seem to get it. For something that is plain indisputable >> physics, people are still running PRE and max RFgain on 80 >> with fast AGC, and are honestly dismayed and confused about >> the inevitable outcome, incorrectly blaming the rig for being >> natively noisy, no-work NR and NB, filter "ringing", unable >> to pull signals out of noise, and more. >> >> Maybe the variable gain by band in the MP (with a menu >> override) was really a better strategy for a default. This >> same issue dogged Orion owners, and by the chatter a lot of >> them never understood either. >> >> There IS something entirely separate with the headphone audio >> and HI-Z headsets, high volume levels, maybe a sharp >> saturation point, and mush, just haven't nailed it yet. >> >> 73, Guy. >> >> On Mon, Feb 8, 2010 at 12:01 PM, Joe Subich, W4TV >> <li...@subich.com> wrote: >> >>> >>>> Likely? I don't know. >>>> >>> Likely is a better choice since raising the AGC threshold >>> >> seems to be >> >>> the primary goal of much of the "PRE/ATT/RF Gain dance" we've seen >>> recently. >>> >>> The hardware AGC (HAGC) would seem to provide an ultimate limit on >>> level to the ADC - unless the ADC can't handle the >>> >> transient peaks - >> >>> so a higher threshold for the DSP derived AGC would be >>> >> helpful in many >> >>> ways. >>> >>> 73, >>> >>> ... Joe, W4TV >>> >>> >>> >>> >>> >>>> -----Original Message----- >>>> From: elecraft-boun...@mailman.qth.net >>>> [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Lyle Johnson >>>> Sent: Monday, February 08, 2010 11:24 AM >>>> To: elecraft@mailman.qth.net >>>> Subject: Re: [Elecraft] K3 DSP AGC Question >>>> >>>> >>>> Hello Joe! >>>> >>>>> Assuming that the threshold values have not changed in a >>>>> >> major way >> >>>>> since Jack's measurements, would it be possible to >>>>> >> extend the range >> >>>>> of threshold values - say to AGC THR=016 at about -80dBm >>>>> >> (assuming >> >>>>> 2 dB per step)? >>>>> >>>>> >>>> Possible? Yes. >>>> >>>> Likely? I don't know. There are a lot of side effects >>>> >> that happen >> >>>> when the threshold is raised... >>>> >>>> 73, >>>> >>>> Lyle KK7P >>>> >>>> >>> ______________________________________________________________ >>> 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 >> > > ______________________________________________________________ > 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 > ------------------------------------------------------------------------ > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 9.0.733 / Virus Database: 271.1.1/2677 - Release Date: 02/09/10 > 02:35:00 > > ______________________________________________________________ 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
