fix figure ref

Author: 777arc

content/sampling.rst

@@ -252,7 +252,7 @@ The figure in the "Receiver Side" section demonstrates how the input signal is d
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 Baseband and Bandpass Signals
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-We refer to a signal centered around 0 Hz as being at "baseband".  Conversely, "bandpass" refers to when a signal exists at some RF frequency nowhere near 0 Hz, that has been shifted up for the purpose of wireless transmission.  There is no notion of a "baseband transmission", because you can't transmit something imaginary.  A signal at baseband may be perfectly centered at 0 Hz like the right-hand portion of this figure :ref:`downconversion-figure`. It might be *near* 0 Hz, like the two signals shown below. Those two signals are still considered baseband.   Also shown is an example bandpass signal, centered at a very high frequency denoted :math:`f_c`.
+We refer to a signal centered around 0 Hz as being at "baseband".  Conversely, "bandpass" refers to when a signal exists at some RF frequency nowhere near 0 Hz, that has been shifted up for the purpose of wireless transmission.  There is no notion of a "baseband transmission", because you can't transmit something imaginary.  A signal at baseband may be perfectly centered at 0 Hz like the right-hand portion of this figure :ref:`_downconversion-figure`. It might be *near* 0 Hz, like the two signals shown below. Those two signals are still considered baseband.   Also shown is an example bandpass signal, centered at a very high frequency denoted :math:`f_c`.
 
 .. image:: ../_images/baseband_bandpass.png
    :scale: 50%