aliasing error question

Started by bos1234 May 13, 2010
Consider the system below. At point B it is graphed. The question is what
is the value of the signal at 15Khz. And what is the aliasing error at this
frequency.

Why did they minus F_s-f=45 in the solution. And what is the value of the
aliasing error mean?

[IMG]http://i41.tinypic.com/idbrjm.png[/IMG]

at Point A and B respectively

[IMG]http://i39.tinypic.com/kas1mp.png[/IMG]

[IMG]http://i40.tinypic.com/9k5yra.png[/IMG]




On May 13, 8:02&#2013266080;pm, "bos1234" <suren130@n_o_s_p_a_m.gmail.com> wrote:
> Consider the system below. At point B it is graphed. The question is what > is the value of the signal at 15Khz. And what is the aliasing error at this > frequency. > > Why did they minus F_s-f=45 in the solution. And what is the value of the > aliasing error mean? > > [IMG]http://i41.tinypic.com/idbrjm.png[/IMG] > > at Point A and B respectively > > [IMG]http://i39.tinypic.com/kas1mp.png[/IMG] > > [IMG]http://i40.tinypic.com/9k5yra.png[/IMG]
Hi, Its clear that the sampling frequency is 60 KHz. This means that all signals between -30 KHz to 30 KHz will be represented as is. Howoever signals whose frequency is outside the range of -30 Kz to 30 KHz will get aliased to those in the range od -30 to 30 KHz. Hence if there is a signal at 45 KHz, it will get aliased as 15 KHz signal, i.e. it will appear as though it were a 15 KHz signal (case of undersampling). Hence 45 KHz is considered in the solution. The level of the 45 KHz signal is the value of the aliasing error. Hope this helps. Regards suren
great explanation. Understood! Just one question. Could I say that the
frequencies from 30-50Khz are the frequencies that are aliased with the
original plot?
On May 14, 10:20&#2013266080;am, "bos1234" <suren130@n_o_s_p_a_m.gmail.com> wrote:
> great explanation. Understood! Just one question. Could I say that the > frequencies from 30-50Khz are the frequencies that are aliased with the > original plot?
Yes. All frequecies from 30 -50 KHz will get aliased. suren