For those interested in evaluating their K2's drift without access to test equipment, here's a process created by John Grebenkemper, KI6WX, while testing the original PLL active frequency compensation mods back in 2003.
This procedure will identify the drift in the PLL reference oscillator separately from the BFO oscillator. That's really handy to know if you think your drift is excessive. Otherwise, you don't know which oscillator is causing the drift. Also, on some bands the drift in the BFO oscillator will cancel the drift in the PLL Reference oscillator. That tends to make the K2 seem as though it's very stable on some bands and not so stable on other bands. You'll need a signal you can receive that is very stable over time. The accuracy of the measurement depends upon this, and we're looking for drifts of a few Hz! A good signal is a standards frequency signal such as WWV in the USA at 10 MHz or CHU in Canada. Step 1: Tune in the on-air signal in CW mode selecting the normal sideband (no bar above the C on the display). Carefully zero beat it using the K2's SPOT function, then note the reading on the K2's frequency display. If you're listening to WWV or some other signal with a steady tone modulation, be careful not to zero beat to the sideband of the tone. If you do, your results will be in error by the amount of the tone frequency unless you zero beat to the same tone later. If using WWV, recommend you wait for a silent period to confirm that you are zero beat to the carrier, which should be producing a tone in the K2's speaker equal to the sidetone frequency you're using. We will call the frequency shown in the K2's frequency display "f1cwn", for "frequency 1, CW normal". Step 2: Switch to CW RV, then re-zero beat the carrier to the SPOT tone. We will call this frequency "f1cwr" for "frequency 2, CW reverse". Step 3: Now you wait until you're ready to take a second set of reading to see how much the K2 has drifted. You can go ahead and have some QSO's or just leave the rig running, whatever you want. When running the drift tests, we transmitted at full power into a dummy load for a period of time to simulate some intensive on-air activity. Step 4: Repeat the above measurements taken in Step 1 and Step 2. Call these measurements "f2cwn" and "f2cwr" for "frequency 2 cw normal" and frequency 2 cw reverse". Step 5: Now we calculate the total drift as follows. Subtract f2cwn from f1cwn. Multiply the result by 1000 since the K2 displays KHz and we want to work in Hertz. Algebraically, this is: Delta (i.e. change in) fcwn = 1000(f2cwn - f1cwn) Delta fcwr = 1000(f2cwr - f2cwr) Step 6: Now we calculate the individual drift that has occurred in the BFO oscillator and the PLL reference oscillator as follows: Delta fpll = (delta fcwn + delta fcwr)/2 Delta fbfo= (delta fcwn - delta fcwr)/2 In my K2 I tested the drift at ambient room temperature, +26C, then operated the rig at 100 watts sending CW from a buffer into a dummy load until the internal temperature reached +42C as measured by a probe mounted inside the closed-up rig. The KPA100's heat sink was too hot to leave my hand on it. The maximum drift I found was less than 50 Hz on any band under those extreme conditions. As they say, your mileage may vary, but that should be typical. If you have an old K2 like mine (S/N 1289) that has never been upgraded, it's a worth while effort if you notice any drift. The PLL reference oscillator stability mods were included in all kits after S/N 3446, according to the information on the Elecraft WEB site. Like most improvements to the K2, Elecraft provides an inexpensive kit of parts and instructions you can use to upgrade your K2. Order E850138, K2 Temperature Compensated PLL Reference Upgrade. If your K2 has a serial number earlier than 3000, you'll also need BFOMDKT, K2 BFO Toroid & PLL Ref Osc Xtal Upgrade. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
