Posted by
Don Wilhelm-3 on
Apr 25, 2006; 12:40pm
URL: http://elecraft.85.s1.nabble.com/Need-help-for-sick-K1-tp389102p389127.html
Darrell,
Since the limit of tuning precision for the K2 is 10 Hz, there is no benefit
to be derived by attempting to tune WWV or other standard frequency station
to less than 10 Hz - and that is well within the error range presented by a
computer soundcard. In other words, even if the error in the soundcard is 5
Hz, the tuning of the K2 will be as close as you can get.
Any error from a high frequency clock will be derived from a 'countdown' of
the computer clock or other crystal controlled clock. Even though a 1%
error on a 14 MHz clock is 140 kHz, when you divide it down to audio, the
same 1% error in the clock on a 100 Hz tone is only 1 Hz - and most computer
reference frequencies are much more accurate than the 1% I used as an
extreme example.
The same is true of the SPOT tone in the K2, it is derived from the 4 MHz
reference oscillator, and with just setting the C22 trimmer to midpoint the
frequency error will likely be less than 1 kHz - that is an error of one
part in 4000 which is only .025% error - when that same error is applied to
a 600 Hz tone, the error is only 0.15 Hz.
So it would seem to me that there is little actual need for calibration of
the computer soundcard spectrum analyzer. If the computer clock is so far
off that the soundcard is greatly in error, that fact should be obvious from
other 'funny happenings'.
73,
Don W3FPR
> -----Original Message-----
> Please expand on this. I have never used a PSK application, but
> how would it
> detect the subcarrier is exactly at 100 Hz? I suspect the
> software is using
> the soundcard clock as a reference and that wouldn't necessarily be very
> accurate.
>
> Seems that the K2 can be set very exactly using Wayne's method
> (
http://www.elecraft.com/Apps/K2%20C22%20Adjust%20App%20Note.pdf) but it
> requires properly zero beating WWV. Using an audio spectrum
> analyzer such as
> Spectrogram to detect WWV's broadcast tones is dependant on the
> accuracy of
> the spectrum analyzer.
>
> The spot tone generator in the K2 seems to derive it's clock and
> therefore
> it's frequency from the MCU and the 4.0 MHz oscillator set by C22, so the
> spot tone frequency will be dependant on the setting of C22,
> which is what we
> are trying to set in the first place. So using this tone as a
> reference does
> not look like it will work.
>
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