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Re: [Discuss-gnuradio] Welcome and brief update
From: |
Chris Albertson |
Subject: |
Re: [Discuss-gnuradio] Welcome and brief update |
Date: |
Sat, 11 Jan 2003 21:32:25 -0800 (PST) |
OK, basic radio theory.
The "tunner" is really a kind of filter that letts the 107.5Mhz
signal pass. It don't move the signal.
THe next stage is a "mixer". Here the 107.5Mhz signal
get mixed with, lets say a 50Mhz sin wave signal. THe result
is a signal with frequency compnents at both 107.5+50 and
at 107.5-50 Mix that signal in another mixer with (say)
40Mhz and then apply filters and you have a 10.7Mhz signal
that you can sample at 30Msps. In a real system the numbers
would be all diferent but the result the same, you "mix and
filter" the desired radio freq. down to a standardized "IF"
freq. and then sample it.
It works because the content being carried by the 107.5 carier is
maybe just voice or NTSC video.
--- Marshall White <address@hidden> wrote:
> --- Daniel Rogers wrote:
> > actually, it seems that I choose 40Msps from a lack of
> understanding of
> > the amount of samples/Hz of radio frequency needed for correct
> digitization.
> >
> > That said, how is it that a 400 kHz sample rate is sufficient for a
>
> > 107.5 MHz FM modulated signal? How is it that you can extract
> useful
> > information when you have much muhc less that one sample per cycle.
> >
> > And given all this information, what is the max frequency you could
>
> > demodulate at 40Msps?
> >
> > --
> > Dan
> >
>
> Dan,
>
> The answer is that you must have a "tuner" that takes the signal at
> 107.5 MHz and "moves" it down
> to a much lower frequency (called an IF, or intermediate frequency).
>
> If you have a 40 MHz sampling rate, any IF less than 20 MHz should
> more or less be okay.
>
> If you had a 400 kHz sampling rate, then your IF would have to be
> CENTERED at 100 kHz.
>
> Marshall
>
>
>
>
>
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> http://mail.gnu.org/mailman/listinfo/discuss-gnuradio
=====
Chris Albertson
Home: 310-376-1029 address@hidden
Cell: 310-990-7550
Office: 310-336-5189 address@hidden
KG6OMK
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- [Discuss-gnuradio] Welcome and brief update, Eric Blossom, 2003/01/10
- Re: [Discuss-gnuradio] Welcome and brief update, Daniel Rogers, 2003/01/10
- Re: [Discuss-gnuradio] Welcome and brief update, Mark Smith, 2003/01/10
- Re: [Discuss-gnuradio] Welcome and brief update, John E. Perry, 2003/01/13
- Re: [Discuss-gnuradio] Welcome and brief update, Tanner Lovelace, 2003/01/13
- [Discuss-gnuradio] Direct Conversion vs Superheterodyne, Tanner Lovelace, 2003/01/13
- Re: [Discuss-gnuradio] Direct Conversion vs Superheterodyne, Mark Smith, 2003/01/13
- Re: [Discuss-gnuradio] Direct Conversion vs Superheterodyne, David Bengtson, 2003/01/13
- Re: [Discuss-gnuradio] Direct Conversion vs Superheterodyne, Mark Smith, 2003/01/14
- Re: [Discuss-gnuradio] Direct Conversion vs Superheterodyne, Lisa Bengtson, 2003/01/14
- Re: [Discuss-gnuradio] Direct Conversion vs Superheterodyne, Mark Smith, 2003/01/14
- Re: [Discuss-gnuradio] Direct Conversion vs Superheterodyne, David Bengtson, 2003/01/14