> Andor wrote:
>
> ...
>
>> Are you saying that A/D converters don't generate a train of dirac
>> impulses for sampling?
>
> No Diracs and -- get ready for this, are you sitting down? -- there
> are no tooth fairies, either. :-)
That's not true! I have an Agilent DG1001 (Dirac Generator) sitting right here on my desk...
--
% Randy Yates % "Maybe one day I'll feel her cold embrace,
%% Fuquay-Varina, NC % and kiss her interface,
%%% 919-577-9882 % til then, I'll leave her alone."
%%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO
http://home.earthlink.net/~yatescr
Reply by Vladimir Vassilevsky●September 20, 20072007-09-20
Jerry Avins wrote:
> cincydsp@gmail.com wrote:
>
>
>> ... Stupid analog electronics and their parasitics.
>
>
> Welcome to the real world, where all engineering starts and ends.
Na. In the real world, the engineering starts at 7 and ends at 5.
VLV
Reply by Jerry Avins●September 20, 20072007-09-20
Andor wrote:
...
> Are you saying that A/D converters don't generate a train of dirac
> impulses for sampling?
No Diracs and -- get ready for this, are you sitting down? -- there are
no tooth fairies, either. :-)
Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by Jerry Avins●September 20, 20072007-09-20
cincydsp@gmail.com wrote:
> ... Stupid analog electronics and their parasitics.
Welcome to the real world, where all engineering starts and ends.
Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●September 19, 20072007-09-19
On Sep 19, 11:58 am, Andor <andor.bari...@gmail.com> wrote:
> On 19 Sep., 15:37, cincy...@gmail.com wrote:
>
>
>
> > On Sep 19, 2:29 am, Andor <andor.bari...@gmail.com> wrote:
>
> > > Jon wrote:
> > > > With current A/D technology, what is the upper limit of what can be
> > > > directly sampled? Super-nyquist is OK -- I'm wondering about the
> > > > highest absolute frequency that can be directly sampled in any practical
> > > > sense. Could I directly sample a 900MHz GSM antenna? Or a 1.8G CDMA
> > > > antenna? How high can you go?
>
> > > Theoretically, sampling only requires a finite band, not necessary
> > > lowpass bandlmitation. So if you are sampling with frequency Fs, you
> > > can perfectly reconstruct a signal that lies in the interval
>
> > > [k Fs/2, (k+1) Fs/2]
>
> > > for any k in {0, 1, 2, ... }, provided you know k. Note that there is
> > > no upper limit on k.
>
> > > Regards,
> > > Andor
>
> > Practically, however, the input frequency response of the A/D
> > converter will diminish enough to impose some limit on what k you can
> > actually achieve. For signals at too high of a frequency, there's not
> > enough time for the input capacitance on the converter to charge/
> > discharge to the right voltage before it's sampled! Stupid analog
> > electronics and their parasitics.^
>
> Are you saying that A/D converters don't generate a train of dirac
> impulses for sampling?
>
> :-)
Oh no, don't get that can of worms open again!
Jason
Reply by Andor●September 19, 20072007-09-19
On 19 Sep., 15:37, cincy...@gmail.com wrote:
> On Sep 19, 2:29 am, Andor <andor.bari...@gmail.com> wrote:
>
>
>
>
>
> > Jon wrote:
> > > With current A/D technology, what is the upper limit of what can be
> > > directly sampled? Super-nyquist is OK -- I'm wondering about the
> > > highest absolute frequency that can be directly sampled in any practical
> > > sense. Could I directly sample a 900MHz GSM antenna? Or a 1.8G CDMA
> > > antenna? How high can you go?
>
> > Theoretically, sampling only requires a finite band, not necessary
> > lowpass bandlmitation. So if you are sampling with frequency Fs, you
> > can perfectly reconstruct a signal that lies in the interval
>
> > [k Fs/2, (k+1) Fs/2]
>
> > for any k in {0, 1, 2, ... }, provided you know k. Note that there is
> > no upper limit on k.
>
> > Regards,
> > Andor
>
> Practically, however, the input frequency response of the A/D
> converter will diminish enough to impose some limit on what k you can
> actually achieve. For signals at too high of a frequency, there's not
> enough time for the input capacitance on the converter to charge/
> discharge to the right voltage before it's sampled! Stupid analog
> electronics and their parasitics.^
Are you saying that A/D converters don't generate a train of dirac
impulses for sampling?
:-)
Reply by ●September 19, 20072007-09-19
On Sep 19, 2:29 am, Andor <andor.bari...@gmail.com> wrote:
> Jon wrote:
> > With current A/D technology, what is the upper limit of what can be
> > directly sampled? Super-nyquist is OK -- I'm wondering about the
> > highest absolute frequency that can be directly sampled in any practical
> > sense. Could I directly sample a 900MHz GSM antenna? Or a 1.8G CDMA
> > antenna? How high can you go?
>
> Theoretically, sampling only requires a finite band, not necessary
> lowpass bandlmitation. So if you are sampling with frequency Fs, you
> can perfectly reconstruct a signal that lies in the interval
>
> [k Fs/2, (k+1) Fs/2]
>
> for any k in {0, 1, 2, ... }, provided you know k. Note that there is
> no upper limit on k.
>
> Regards,
> Andor
Practically, however, the input frequency response of the A/D
converter will diminish enough to impose some limit on what k you can
actually achieve. For signals at too high of a frequency, there's not
enough time for the input capacitance on the converter to charge/
discharge to the right voltage before it's sampled! Stupid analog
electronics and their parasitics.
Jason
Reply by Andor●September 19, 20072007-09-19
Jon wrote:
> With current A/D technology, what is the upper limit of what can be
> directly sampled? Super-nyquist is OK -- I'm wondering about the
> highest absolute frequency that can be directly sampled in any practical
> sense. Could I directly sample a 900MHz GSM antenna? Or a 1.8G CDMA
> antenna? How high can you go?
Theoretically, sampling only requires a finite band, not necessary
lowpass bandlmitation. So if you are sampling with frequency Fs, you
can perfectly reconstruct a signal that lies in the interval
[k Fs/2, (k+1) Fs/2]
for any k in {0, 1, 2, ... }, provided you know k. Note that there is
no upper limit on k.
Regards,
Andor
Reply by mnentwig●September 19, 20072007-09-19
One problem is timing jitter:
A given sampling time offset (in seconds) leads to an error voltage that
is proportional to dV/dt, where V is the signal voltage.
Naturally, dV/dt increases proportionally with the signal frequency.
This can hurt subsampling schemes badly, because the resulting error may
appear as white noise over the whole bandwidth: The smaller the
bandwidth-to-signal ratio, the more jitter-related noise folds inband and
hits the signal.
Cheers
Markus
Reply by Eric Jacobsen●September 18, 20072007-09-18
On Tue, 18 Sep 2007 20:28:09 -0400, Jon Mcleod
<jonmcleod2003@yahoo.com> wrote:
>With current A/D technology, what is the upper limit of what can be
>directly sampled? Super-nyquist is OK -- I'm wondering about the
>highest absolute frequency that can be directly sampled in any practical
>sense. Could I directly sample a 900MHz GSM antenna? Or a 1.8G CDMA
>antenna? How high can you go?
How high do you want it to go? How much do you want it to cost?
Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org