[opendtv] Re: DVB-T HDTV demo using 19.7 Mbps in a 6 Mhz channel in costa rica
- From: "nat ostroff" <nostroff@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 6 Mar 2006 20:06:51 -0500
I could not have said this better myself. Wait a minute! We did say this in
1999.
It is ashamed that so many were sold a "bill of goods" on ATSC and lacked
the ability to see just a little into the future. I guess they were blinded
by the stream of enlighten rhetoric from our industry leaders.
Nat Ostroff
----- Original Message -----
From: "Stephen W. Long" <longsw@xxxxxxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Monday, March 06, 2006 7:13 PM
Subject: [opendtv] Re: DVB-T HDTV demo using 19.7 Mbps in a 6 Mhz channel in
costa rica
> Since Doug is so full of him self this evening, lets discuss this a little
> further. These comments echo part of my discussions with the FCC years
ago:
>
> In the far field, you are going to need an antenna to receive a signal.
> Since many stations tend to have antennas in the same part of town, folks
> in the far field can receive all of the stations without repointing the
> antenna. If you are going to all of the trouble to have a 30' antenna,
the
> selection of a 3db preamp to pull in a COFDM signal is no big deal. In
the
> far field, big antennas and preamps are the norm, and I would assert there
> is no practical difference in the two systems. BTW, there are very few
> viewers in the far field - at least few when it comes to ratings numbers
> which is what a station cares about anyway.
>
> The differences in the two systems are in the NEAR field - where all the
> people live. COFDM is superior in the near field - the echos of
buildings,
> etc. make reception BETTER, and you do not have to repoint the antenna
just
> to change a channel. As demonstrated at NAB in 1999 you can have a
> robust/mobile SD channel and an HD channel in the same bandwidth using
> COFDM. More importantly, in the event of a local emergency, COFDM modes
> can be switched to maximize robustness to punch through to all receivers -
> to portable receivers hiding in the basement. You do not have such
> flexibility with ATSC 8VSB.
>
> With regards to the 30' antennas - what a joke. Like anyone in a city
> gives a hoot about installing a 30' antenna to receive TV. I want a stub
> antenna on the back of the set - just like my cell phone. I could have
> this with COFDM, I will never have it with ATSC. Out in the country, it
is
> common to have big antennas. Given the differences in behaviors by real
> consumers in the near and far fields, there is NO advantage to ATSC.
>
> Stephen Long
>
> At 10:51 AM 3/6/2006 -0600, you wrote:
> >John Shutt wrote:
> >
> >>
> >> What is the point of your quote? It reinforces what was actually
observed
> >> in the field by over a hundred different observers over the course of a
> >> summer in 1999. You think you can tell the difference in 2 dB of
> >> sensitivity in your living room with your receiver? Atmospherics alone
> will
> >> make the signal vary by more than 2 dB.
> >>
> >
> >You BET I CAN tell a 2 dB difference, and it is large and
> >obvious.
> >
> >Actually, of course, the difference is still more like 3 dB
> >between COFDM and ATSC, but let's say 2 dB because it's
> >still a big difference in reception.
> >
> >I have a station I watch frequently that is some 68 miles
> >away. I get if off an indoor antenna, a 16 element Yagi
> >sticking out a window. This is attached to a preamp
> >with a 0.6 dB [sic] NF, which is is tuned for the
> >channel of interest, though the 3 dB NF bandwidth is +- 4
> >channels.
> >
> >The signal is quite reliable with this setup. I get dropouts
> >for periods of a hour or so in the evening every 10 days or
> >so in early winter. The signal on a spectrum analyzer is
> >near perfectly flat when reception is OK. Typically the
> >S/N on the receiver is in the 16.5-18 dB range. The failures
> >start when it starts dropping below 16 dB into the middle
> >15s. The S/N shown on the receiver meter corresponds to the
> >power level shown on the spectrum analyzer as long as the
> >spectrum is flat. In some reception conditions, in very cold
> >winter conditions just after sunset, I start seeing a
> >non-flat spectrum that varies on a 1 second time scale.
> >These are very broad frequency drops, not sharp dips; as
> >they vary in frequency you can see them move around inside
> >this channel (which is 44) and also the same drops appear
> >just as expected by extrapolation in a channel 42 station
> >which is the same power, height, and on a tower about one
> >mile away from 44. If the average level drops below 16 dB,
> >I start seeing dropouts.
> >
> >Now, I have frequently tried inserting a 2 or 3 dB
> >attenuator right at the input of the preamp. This has a
> >DRAMATIC influence on reliability in any season except
> >Aug-Oct. Instead of normally having completely reliable
> >reception, it becomes quite iffy. Some days it is fine, but
> >in early winter it is almost always zip, none, nothing all
> >evening. In late fall or spring/early summer it becomes
> >perhaps 75% reliable, which is near useless, compared to the
> >normal >99.9% reliability.
> >
> >So I can say that IN THE ACTUAL REAL WORLD, 2 or 3 dB makes
> >a HUGE difference in actual real world useability of a station.
> >
> >Now there is also another thing: that ch. 42 is, except in
> >late summer/early fall, virtually NEVER receivable, even
> >though the spectrum analyzer shows it to be exactly the same
> >signal strength as 44 (and the NF of the receiver is still
> >probably 1 or 1.3 dB at Ch. 42). This is because there is a
> >channel 41 digital signal that is typically 40 dB stronger.
> >When the propagation of 42 is good enough that the signal
> >levels are less than 35 dB different, I get 42 OK.
> >
> >So in fact 2 dB DOES certainly make a REAL difference, at
> >least in the far field.
> >
> >Doug McDonald
> >
> >
> >
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