Re: How does digital TV broadcast prevent ghosting effects?

Glenn Gundlach wrote:
On Nov 21, 1:57 pm, AZ Nomad <aznoma...@xxxxxxxxxxxxxxxxxxx> wrote:
> On Wed, 21 Nov 2007 10:11:28 -0800 (PST), MRW
<mr.whate...@xxxxxxxxx> wrote:
> >Good morning world!
> >I've been reading about the new digital TV standards (8-VSB, DVB-
T,
> >ISDB-T) and they all mention that the standards are more robust
> >compared to the analog standard. For example, all state that
> >practically ghosting effects are eliminated with DVB-T and ISDB-T
> >providing more robust response to mulitpath effects than 8-VSB.
> >How do these standards eliminate ghosting effects?
>
> step 1) get a clue at what ghosting is
>
> When you've done this then you'll understand why ghosting is
impossible
> with digital transmission.

Multipath is a large problem in digital transmission though it doesn't
manifest itself as trailing edge smears in the picture. It shows up as
lumps in the RF response (comb filtering) that make it difficult to
impossible to extract the data. There are active equalizers that can
correct some pretty bad reflections. The newest chipsets (#6 coming
soon) can correct a broader range of errors and do it faster - almost
to the point of working in a moving car.

http://www.hdtvprimer.com/ISSUES/what_is_ATSC.html


The Vizio set I just bought does a fairly good job here. It did decode a few streams where I was almost sure it wouldn't. But not all because multipath is really bad out here.

Question: How do you find out what's on those digital channels? Ok, I found some via the local station web sites, such as 13.1 or 13.2. But then others are scattered. For example 54.1, 54.2 and 54.4 are listed under KTEH whereas 54.3 is on the KQED web site. The latter is confusing because it is listed as channel 9 out of San Francisco. Our TV guide here turns out not to be very useful because it only lists the analog channels for OTA stations, the rest is all cable and satellite.

--
Regards, Joerg

http://www.analogconsultants.com/
.

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