[Elecraft] Spectrogram and frequency markers

[Sverre Holm]

When I teach DSP I have sometimes dissected a PC soundcard and shown the
students. What seems to be the case is that the usual 48000 kHz sampling
clock, is derived from a crystal running at 24.576 MHz (divide by 512).
The other sampling rates like 44.1, 32, 16, 8 kHz etc are done digitally
by interpolation and resampling. So, the basic accuracy comes from the
crystal where e.g. 1 ppm gives 0.048 Hz error in 48 kHz. 

Then the frequency resolution is due to the FFT length, e.g. sampling
rates 11.025 kHz and 1024 point FFT gives you a 10.7666 Hz resolution. I
am assuming that there is no interpolation for increased peak location
accuracy after the FFT. This will be the main source of inaccuracy in
the marker setting in Spectogram as the bins will be centered at
n*10.7666 Hz, e.g. if you want 600 Hz it will be either 592.2 Hz or
602.9 . The conclusion is that this is not a major problem in setting
the K2 to something like 30 Hz accuracy.

--
73, 
Sverre

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Sverre Holm, LA3ZA
www.qsl.net/la3za