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*Subject*: Silly question or is it?*From*:conrad@xxxxxxxxxxxxxxxx>*Date*: Sun, 12 Jan 2003 19:39:14 -0000

I am about to show my ignorance but there is something I don't understand fully. 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 G0RUZLINRADDARNIL