[linrad] Silly question or is it?

["Conrad G0RUZ" <conrad@xxxxxxxxx>]

I have been thinking about the IQ receiving scheme. I am not sure that I
have grasped exactly what is going on. If I understand correctly the Nyquist
theory says that the frequencies reproduced accurately are a little below
1/2 the sampling rate. So for a 96kHz sampling rate the maximum accurately
reproduced frequency will be around 46kHz. The anti alias filters in the
Delta 44 are presumably set a little below 48kHz. This explains how, when
sampling at 96kHz, if you don't choose IQ mixing in Linrad you only get a
48kHz wide display on the waterfall graph. When you go to IQ this gets twice
as wide, I am not absolutely sure why this is and I would like a simple
explanation if possible.

Also my uncalibrated system at the moment shows a big nasty spur at 48khz or
so, does the calibration routine remove it? If so how?

Sorry for the simple questions but I would really like to know what exactly
is going on. I think that there are many who don't understand this.

73

Conrad G0RUZ



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