[opendtv] Re: DVB-T HDTV demo using 19.7 Mbps in a 6 Mhz channel in costa rica
- From: Doug McDonald <mcdonald@xxxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Tue, 07 Mar 2006 08:32:38 -0600
Stephen W. Long wrote:
> 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.
In that last statement you are wrong. That's part of the
problem. You are, as typically, thinking "big city".
Our transmitters are all over the compass. True, they tend
to come in near colocated pairs, but that's it.
> 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.
A 3 dB preamp likely won;t pull in a COFDM signal where I
live, even with a 30 foot antenna. ATSC, which requires 3 dB
less signal, requires a 0.6 dB preamp with a 25 foot antenna
(indoors, but its a big window.) A 4 dB preamp or a 3 dB
attenuator results in great unreliability with my present
setup. The extra 5 feet would likely mean that ATSC would
work with a 3 dB preamp. COFDM would not (at the same bitrate).
> In the
> far field, big antennas and preamps are the norm, and I would assert there
> is no practical difference in the two systems.
And I assert that there IS a big difference: 3 dB
Doug McDonald
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