My tests were done as part of the work John, KI6WX, did in developing and testing the thermister frequency compensator that is now a part of the K2 design. That was back in 2002.
As you know, the drift is worse on higher frequencies, and it depends upon the stability of both the BFO and VFO variable crystal oscillators. My K2 was pretty typical of the day. On 15 meters I'd expect to see about 150 Hz drift just receiving for 30 minutes from a "cold start". Normal transmitting might pushed the drift to 210 Hz. After installing the temperature compensator, the worst case situation, running the internal air temp from 70F to 120F (which made the heat sink too hot to leave my hand on) resulted in a worst band drift of 50 Hz and less than 20 Hz on most bands. It's much lower than that in normal use. Even though I'm a long-winded CW rag chewer the temperature never approaches what it was while testing the compensator. The temp compensation circuit became part of the production units at about S/N 3446. If you have an earlier unmodified K2 this would be a worthwhile change. IIRC it also included a change to a NPO cap in the BFO circuit to improve that oscillator's stability as well. You can further "tweak" the compensation circuit by changing the value of Ra in the circuit. That's the 27K resistor in series with the input to the op amp in the compensator. Values from 15k to 56k can be used to adjust the compensation further. Ron AC7AC -----Original Message----- Subject: Re: [Elecraft] Successfully using a micro fan to keep K2 cool Well, I like mine cool. In my experience, cool equipment has fewer breakdowns and lasts longer. Not only that, it has less drift. There is a menu in K2 to calibrate the temperature probe that controls the fan. I have mine set to a much higher temperature than what it actually is. This makes the fan come on at a lower temperature. I just put up with the noise. My K2/100 drifts about 70 Hz from a cold turn on in the mornings to "ambiant." If I begin rag chewing and really pound away it will drift another 40 Hz. I live with this every day, and although it gives me something to do while rag chewing, but I'd be happy to improve the temperature stability further and reduce it a bit more. So, Ron, It got hot enough you couldn't put your hand on it... How far did it drift ? TR, WB6TMT K2 S/N 838 ______________________________________________________________ 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
