[opendtv] Re: News: Free but Fickle, DTV Eludes Some
- From: Albert Manfredi <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 5 Mar 2009 21:48:59 -0500
Craig Birkmaier posted:
> Free but Fickle, DTV Eludes Some
>
http://www.tvnewsday.com/articles/2009/03/03/daily.2/
The article says, among other things:
"The dirty little secret about digital is that it doesn't have nearly the
coverage of analog."
The real truth is, most of these articles don't educate or elucidate, they go
for dramatic effect.
Sometimes the reception problems are explained by people expecting VHF-only
antennas to work for UHF too. Sometimes the problem is that the DTV station is
at still too low power. I'll bet that many times, the problem is that the
"successful" analog reception was very poor, but the interviewee was never
explained about the digital cliff. Rarely are all the facts given, and this
article is no exception.
I did a tvfools.com experiment, to see what this one tool says about analog vs
digital signal strength for stations that are good or marginal.
The analog signals that these interviewees usually rave about are most likely
local VHF stations. In my case, using my current antenna height of ~3':
analog VHF digital (all UHF)
---------- -------
Ch 4 -33.3 dBm -64.2 dBm
Ch 5 -37.0 dBm -65.7 dBm
Ch 7 -39.8 dBm -66.8 dBm
Ch 9 -41 dBm -61.1 dBm
Hmmm. You think 30 dB difference in signal strength could have some effect? And
yet, those DTV stations are good.
So then I tried to see what a truly grainy and inadequate analog stations would
measure as, and compare it with its digital counterpart. Here are some truly
marginal analog stations, from Baltimore, and the comparative digital strength.
The digital is most often fine, sometimes over the cliff.
analog (UHF) digital (also UHF)
---------- -------
Ch 45 -96.2 dBm -100.4 dBm
Ch 54 -88.7 dBm -97.4 dBm
Going by these numbers, it seems clear that the problem is not so much
"digital," but signal strength differences. And even then, those essentially
unviewable analog stations, 45 and 54, are often beat by their solid digital
counterpart, at lower strength.
I'm think the tvfool numbers are best taken to show comparisons, not absolute
values. I doubt my receivers are really good to -100 dBm. And it is remarkable
that analog stations really can sync up at such low power levels. But truly, I
bet most of the differences in reception are explained by the digital signal
being quite a bit weaker than its analog precedent.
Bert
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