Paul Kirley wrote: >The K3 is capable of displaying frequencies to 1 Hz. It can >be calibrated to somewhat less than 1 Hz against WWV (method 2). > >Because I wanted to see if my K3 serial 1322 was capable of >measuring frequency to its displayed precision, I decided to >attempt the November 11/12 ARRL Frequency Measuring Test. > >I warmed up my K3 for about two hours because--even with the >optional TCXO--my K3 drifts almost 0.1 ppm per degree Centigrade >from 25C to 30C, the latter part of its warmup range this time >of year at my QTH. (0.1 ppm is almost 1 Hz on 40 meters.) > >Then I carefully used method 2 to calibrate against 10 MHz WWV, >checking after exiting REF CAL by tuning across WWV on CW with >SPOT activated to see that the beat notes were similar on each >side of zero beat for 1 and 2 Hz off frequency. (A lack of >similarity indicates that a small tweak of REF CAL is needed.) >Tuning past WWV's carrier on CW with SPOT enabled also provides >practice for the real thing. >
For anyone who has a reliable 10MHz frequency source (eg locked to GPS), another calibration method is to compare this reference against the 10.000000MHz CW output from the K3 using an oscilloscope. The visual display gives much greater certainty than listening to veeeeery sloooow audio beats. Switch the 'scope into X-Y mode, connect the 10MHz reference into the X input, and connect a sniff of RF from the K3 into the Y input. This will display a slowly rotating Lissajous pattern. Carefully "tune" the REF CAL setting until the pattern comes almost to a complete stop. It isn't possible to freeze the pattern completely because REF CAL can only be adjusted in 1Hz steps at 49.380MHz. Even so, you can very quickly find the closest possible 1Hz step, so the error at 10MHz will typically be less than 0.2Hz. The visual display also gives a very clear indication of frequency drift. (Finally, all of these procedures assume that rounding errors in the internal synthesizer arithmetic are of a much lower order than the smallest (1Hz) steps in the VFO and REF CAL tuning.) -- 73 from Ian GM3SEK ______________________________________________________________ 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
