Here are the technical details regarding the K3's VFO tuning accuracy: The K3's PLL synthesizer is phase locked to its 49.38 MHz reference via a DDS chip used as a precision divider. The DDS output is in the 3.6 MHz range, with a step size of 0.184 Hz (49.38 MHz DDS clock divided by 2^28 DDS word size).
Taking the 8.215 MHz 1st IF into account (added to the VCO on 160-10 m, subtracted from the VCO on 6 m), this translates to a VCO step size of about 0.5 Hz on 160 m, 1 Hz on 20 m, and 2 Hz on 6 m. Other bands are between these values. Example: At RF=14 MHz, the VCO is running at around 22 MHz. The ratio between 22 and 3.6 is about 6, and 6 * 0.184 = about 1 Hz. This is the worst-case DDS-related tuning error on 20 m. If REF CAL (in the CONFIG menu) is not set to the exact frequency of the reference oscillator, there will be a small additional offset on all bands that is proportional to the operating frequency. In diversity mode (main/sub VFOs and filter bandwidths set identically), the DDS chips on the two synthesizers are set to exactly the same tuning word, and the VCO outputs are at exactly the same frequency. The two synths are phase-locked to the same signal, so there is never any beat note between the two. This is critical for diversity use, and is lacking in some other transceivers with a sub receiver. 73, Wayne N6KR On Nov 17, 2009, at 10:05 AM, ab2tc wrote: > > Hi, > > First time I have heard about this. How much frequency shift are we > talking > about here? A fraction of a Hz, 10Hz? I have certainly never noticed > this, > but of course on speech anything less than 10Hz is practically > inaudible > unless you do a USB/LSB comparison on an AM station. > > AB2TC - Knut > > > > Wes Stewart wrote: >> >> Guys, >> >> I've mentioned this caviet before: >> >> http://n2.nabble.com/Ref-Osc-Cal-Method-4-td2595451.html#a2595451 >> >> The way the K3 implements the passband shift, the same signal, with >> the >> same VFO setting, will have a different audio beat note if the SHIFT >> control is changed. * >> >> <snip> >> > > -- > View this message in context: > http://n2.nabble.com/K3-frequency-accuracy-versus-displayed-precision-tp4016138p4020213.html > Sent from the Elecraft mailing list archive at Nabble.com. > ______________________________________________________________ > 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
