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Old 9-Mar-2021, 7:06 PM   #30
tripelo
Senior Member
 
Join Date: Jan 2010
Location: Dallas, TX
Posts: 172
Quote:
Originally Posted by videobruce View Post
Post #4 and #7 have been extensively updated.
Sorry about your experience with the Avant-X. Just few minutes ago, posted a couple of comments, inquiring about your Avant-X unit.

Likely, you know this, put it here for others benefit:

A DTV station produces splatter outside the normal ~6 MHz bandwith in both upper and lower adjacent channels.

This splatter appears as noise to a receiver that is trying to demodulate the adjacent channel signal.
If the combination of noise (environmental, thermal, other interference plus the adjacent splatter)
reduces the signal-to-noise ratio to less than about 15 dB then signal cannot be decoded.

In the above case, no amount of frequency rejection of the undesired channel can recover the desired signal.

The FCC sets limits on the splatter:

From:

ATSC Recommended Practice:
Transmission Measurement and Compliance for
Digital Television
Document A/64B, 26 May 2008



As shown in the image the splatter begins at about 36 dB below the flat portion of the DTV channel.

That adjacent splatter is caused by intermodulation distortion (IMD) in the transmitter chain.

Pretty sure many stations perform somewhat better that that shown in the graph,
but it is a tough problem for transmitter chain designers.

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In addition, adjacent splatter can be generated in the TV receiving circuits.

Mainly occurs when signal is very strong.

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Attached Images
File Type: gif Xmtr Splatter.gif (16.3 KB, 435 views)
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