Posted by
Vernon Mauery on
Apr 05, 2011; 9:45pm
URL: http://elecraft.85.s1.nabble.com/Elecraft-K3-Frequency-Calibration-using-Sidetone-tp6243828p6243923.html
On Tue, Apr 5, 2011 at 2:08 PM, David Robertson <
[hidden email]> wrote:
> I see many references using the CW sidetone as a calibration tool for the K3's frequency readout. I fully understand the logic behind using the sidetone but this brings up a question.
>
> What is the reference for the sidetone frequency within the K3? Is in the K3's master oscillator? If you are in fact changing the master oscillator frequency to match K3's readout to an actual frequency, and if the sidetone frequency is derived from the same master oscillator aren't you defeating the purpose of your calibration. It seems logical to me to a method of calibration that your reference is not derived from the same oscillator you are trying to calibrate.
I am not sure what is used to generate the sidetone, but even if it is
the K3 master oscillator, you are probably safe to do it this way.
This is because the master oscillator runs at 48.39 MHz, while your
sidetone is at 400-900Hz. We are talking a 4-5 orders of magnitude
difference here. That means that if you change the frequency by 100Hz
(mine is off by 80 or so), you would only change the sidetone
frequency by 80*10e-4 Hz, which is imperceptible.
But that doesn't take into account the fact that the sidetone is all
local. Your receiver generates the sidetone (of your choosing), which
is N-Hz away from actual chosen pitch, where N is the frequency
difference between the carrier of the signal and your tuned frequency.
Hitting the SPOT button mixes in the chosen sidetone, which then
creates nulls and peaks that are easy to discern even for the tonal
impaired. But since BOTH tones are generated by your K3, it makes
sense that they would change at the same rate, thus negating any
changes from the master oscillator.
> Having said the above here is the method I use.
>
> On usb mode I tune the K3 to the reference standard you are using ( Any AM station such as WWV or any station of a known frequency). I set the readout to the exact known frequency of that station. I note the pitch of the sound I hear from the station (the tone from WWV or CHU works best) . Next I switch to LSB and note the pitch of the sound. If they are identical then the K3 is calibrated. If the pitch changes then you have to configure the master oscillator's frequency so the pitch between USB and LSB match. I relies the above method requires a good ability to note slight changes in pitch. Some of us do not posses that ability and must use a different method. For those that do, this method works.
This is a method I have not heard of, so thank you for sharing it.
--Vernon N7OH
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