Doug, The BFO is obviously the culprit here. What serial number is this K2? Do you have the new L33? with many turns of #36 wire. If this is an older K2, install the BFO upgrade kit. If you already have the upgraded parts, then I suggest you equip yourself with all of the parts in the BFO circuit and just replace them. You can replace them one at a time until you find things more stable, but I believe it is easier to replace them wholesale and see what happens. You will need 2 BFO crystals X3 and X4 C173 and C174 D37 and D38 L33 Replacing L33 will require a high value 1/8 watt resistor to mount the toroid - the K2 lists this as R116 PN E500086.
73, Don W3FPR Douglas Furton wrote: > Hello, all > > I've been bothered with the CW tone/filter setting > on my K2 for some time now. I seem to need to run > CAL FIL daily, at least to have the BFO freq. read > into memory. I observe that the CW tone starts low > and drifts upwards as the rig warms up when I tune a > signal to the center of the filters (maxing the > S-meter). > > Here is some data characterizing the freq. drift > in my K2 (#6761). I measured the PLL and BFO freqs > with a nice frequency counter. I measured these > shifts with the K2 locked at 7050 kHz, and computed > the total shift = dPLL - dBFO (all referred back to > the initial (T=18.5C) measurements. I measured the > temp. with a thermocouple in contact with the PLL > thermistor board. I also measured the PLL and BFO > control voltages at various times and found them > to be constant. > > > Cumulative freq. Shifts > T PLL BFO Total > (C) (Hz) (Hz) (Hz) > 18.5 0 0 0 > 19.3 9 -17 26 > 19.6 13 -34 47 > 20.2 17 -57 74 > 20.8 19 -70 89 > 21.3 24 -79 103 > 21.6 26 -87 113 > 22.0 28 -92 120 > 23.3 37 -124 161 > 24.0 40 -136 176 > 24.5 46 -164 210 > 25.0 53 -205 258 > 25.5 62 -256 318 > 25.5 70 -310 380 > > (I hope the table above remains tabulated > properly. Best viewed with a monospace > font.) > > It seems the thermistor board compensates the PLL > fairly well (although maybe I could tweak RA upwards > a bit), but the BFO drifts considerably, and > since the PLL and BFO drift in opposite directions, > the total drift is exaggerated. > > I may measure the drift on a second band, but these > data are just from 40 m. > > I would really like to improve the temp. stability > of my K2. > > Does anyone have any suggestions? > > Thanks, > > Doug Furton > K8EXB > > ____________________________________________________________ > GET FREE 5GB EMAIL - Check out spam free email with many cool features! > Visit http://www.inbox.com/email to find out more! > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > 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: 9.0.730 / Virus Database: 270.14.150/2632 - Release Date: 01/19/10 > 02:34:00 > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
