Re: Complex to 2x real - how?

On Oct 10, 6:15 am, Randy Yates <ya...@[EMAIL PROTECTED]
> wrote:
> Jerry Avins <j...@[EMAIL PROTECTED]
> writes:
....
>   2. Mix to new sample rate (2*Fs) / 4: this ****fts the
>   spectrum by Fs / 2, so that what was at -Fs/2 to 0 is
>   now at 0 to Fs / 2, and what was at 0 to Fs / 2 is
>   now at Fs / 2 to Fs. Since the new sample rate is
>   2*Fs, Fs is the highest frequency available.
>
>   This preserves the information that was in the
>   negative frequencies of the old complex signal
>   in the positive frequencies of the new real
>   signal.
> ...

>
> The bad thing about this approach is that it inverts
> the spectrum, as seen by the step 2 explanation.
>
> %  Randy Yates

Randy

This doesn't invert the spectrum, it merely ****fts it linearly up in
frequency. When used to demodulate an upper sideband this process
follows a translation of the center of the sideband to DC and a
desampling lowpass filter stage to reduce the bandwidth to match the
bandwidth of the sideband. This complex to real process puts the
entire sideband back above DC and allows use as an audio channel of
the sideband content.

Dale B. Dalrymple