[opendtv] Re: Seeing Ghosts on a Single Frequency Network

  • From: dan.grimes@xxxxxxxx
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Wed, 19 Jan 2011 09:11:51 -0800


I've had problems receiving some ATSC channels that appeared perfect on the
spectrum analyzer, at least at the settings I had it on.  But the article
brings to light that I did not go deep enough into the signal to see what
was really going on.  Can't believe I didn't think of that!  Now I'll need
to see if my low-cost analyzer (<$10K) can scan at those rates/resolution.
Thanks, Mr. Rhodes!

Of course, the phase issue makes perfect sense.  But my guess is that the
receiver antenna wouldn't have to move much to affect the relative phase
between the direct signal and echo.  Of course, for those of us with fixed
antennas on the roof, that adjustment isn't practical.  And my directional
antenna is not exactly a match for an SFN.  However, I'm sure the SFN with
ATSC is really intended for mobile applications, which then begs the
question, how will mobile affect these off-phase echoes?  I'm sure it
depends on the period of the cancelation which is dependent on the speed of
the receiver.

The point is that there are still more variables to be considered in the
ATSC reception from SFNs that may or may not affect these results.  But I
can appreciate the experiment for isolating this particular variable.

Dan

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