[opendtv] Re: Democrats Air Concerns About Analog Switchover

  • From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Mon, 20 Nov 2006 11:21:00 -0500

Craig Birkmaier wrote:

> We've been down this path before Bert. The design of the U.S. OTA
> television system is "MARKET ORIENTED." The ability to receive
> stations from adjacent markets is a "fault condition," based in
> reality that big sticks and high power levels interfere with
> adjacent markets.

Perhaps. I know you think so. My opinion is that any OTA user worth his
salt wants as many stations as he can get. And also, I think more in the
Euro model. Meaning, everyone is expected to use whatever set of
transmitters or translators provides the best signal in his location.
E.g., if I were Cliff, I'd have that nice antenna pointing at Baltimore,
not at Philadelphia.

And we have also discussed, Craig, that in order to create the sharp
boundaries between markets that you seem to prefer would take quite a
large number of transmitter sites. No European SFN does it this way
either. It's not reasonable.

> It is this interference that causes more than half of the the
> spectrum assigned to OTA TV broadcasts to lie fallow. Now the
> broadcasters are concerned about "white space" interference from
> very low power devices, so they do not want anyone to use the DTV
> spectrum lest they lose one of those precious OTA only viewers...

You seem not to appreciate that even low power interference, if it is
generated at a short distance from the receiver, can overwhelm a higher
powered but distant source. Think in terms of inverse square law. Power
density falls off by the square of the distance from the transmitter.

For example, take a 600 MHz, 50 KW ERP transmitter 20 miles distant, and
a 1 W transmitter 10 feet away, transmitting on an adjacent channel.
Using purely free space propagation loss, the distant transmitter
creates a -41 dBm signal level at the receiver, while the little guy
nearby creates a -7.7 dBm signal. That's a hefty 33.3 dB advantage for
the low-power source. A 100 mW local transmitter creates a -17.7 dBm
signal, still a solid 23.3 dB advantage.

In reality, the problem is worse, because the distant source will likely
be attenuated by more than just free space distance, or it may be
somehwat more distant, or whatever. So these numbers could definitely
create a problem.

As to A-VSB compatibility, the way these new features SHOULD become
incorporated is that a manufacturer of 6th gen chips, for example, will
find that he can add A-VSB without significantly affecting the cost of
the new product. So he will use that to get an edge on other vendors. Of
course, as we know, logic goes out the window when it comes to DTT
products in the US.

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