0805. tnx Wayne
On Dec 5, 2011, at 4:31 PM, Paul Christensen wrote: > Wayne, > > For those of us ordering the cap through Mouser or DigiKey, can you > reply > with the SMD/SMT cap dimension code (e.g., 0603, 1608, etc.) > > Tnx! > > Paul, W9AC > > ----- Original Message ----- > From: "Wayne Burdick" <n...@elecraft.com> > To: "Elecraft Reflector" <elecraft@mailman.qth.net> > Sent: Sunday, December 04, 2011 8:50 PM > Subject: [Elecraft] K3 hardware AGC experiment shows promise > > >> Hi all, >> >> The K3's hardware AGC time constant is a compromise between recovery >> time and IMD due to modulation of the loop. C238, on the bottom of >> the >> RF board near the front, sets this time constant. >> >> We did a little experiment today (thanks to Tree, N6TR) that suggests >> increasing the size of C238 substantially might be a worthy change. >> In >> the case of signals just large enough to tickle the hardware AGC, the >> first IMD products were reduced by something like 18 dB. This will >> also increase the recovery time for very strong signals, so the jury >> is out on whether this is OK for the average user. >> >> For the experimentally inclined: C238 is easy to get to; just remove >> bottom cover A (the front half). C238 is a large-ish surface mount >> capacitor nestled between two 20-pin connectors. The present value is >> 0.1 uF. Tree tacked a 1-uF cap on top of it. Then he tacked another >> one on, which improved things by another few dB. >> >> Some ops have mentioned problems with signals much lower than this, >> which has always baffled me. But I got to thinking: Suppose you're >> listening to a bunch of S4-S5 signals in your DSP passband. You could >> have larger signals outside the DSP, but inside the crystal filter. >> Or >> you could have clicks from strong signals that get inside the crystal >> filter but you can't hear because you're using a narrow DSP filter. >> Or >> you could have noise spikes. Any of these could ping the hardware AGC >> just enough to cause IMD between all of the signals in the passband. >> >> My point is that increasing the loop time constant could have a more >> general benefit when a band is busy and/or noisy. >> >> Let me know if you try this and whether the results are of interest. >> (I live in an RF-free zone, it seems, so I can never recreate the >> problem here. Frustrating!) >> >> 73, >> Wayne >> N6KR >> >> >> >> ______________________________________________________________ >> 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
