[opendtv] Re: Genachowski pitches his upcoming national broadband plan
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sun, 28 Feb 2010 07:08:32 -0500
At 7:20 PM -0500 2/27/10, Albert Manfredi wrote:
a) That is also true for big sticks. b) No matter how you try to
rationalize this idea, you will always end up with interference
zones between the adjacent markets, if you try reusing the same
frequencies.
Correct. The difference will be the size (and location) of the
interference zones. With big stick these interference zones can be
huge - but this may not matter since much of the interference occurs
over water or unpopulated areas.
I've had two very different experiences with interference zones.
I had a 50 ft antenna with a rotor when I lived in Alachua (just
north of Gainesville) in 1979-80. At times I could pick up signals
from 2 -3 transmitters on the same channel, although most of the time
they interfered with one another so that none could be tuned in.
There are Channel 10's in Tallahassee, Tarpon Springs and Miami. Most
of the interference between Tampa and Miami is over the Everglades;
between Tampa and Tallahassee it's mostly the Gulf of Mexico and a
bunch of sparsely populated counties in the Big Bend. What I had a
hard time with was reception of Jacksonville stations (about 60
miles) because of temperature inversions over the St. Johns river.
There are TV station microwave links between Jacksonville and
Gainesville that suffer from the same problem.
When I lived in Grass Valley California, I stayed in a cabin that
looked out over the Central valley, some 1800 feet below. At times I
could receive more that 20 channels from Bakersfield to the South,
San Francisco and Sacramento to the west, and Chico to the North. At
other times I could hardly watch anything because of weather and
interference.
Bottom line, the big sticks send signals that can travel VERY LONG
distances, and natural phenomenon are constantly changing the
interference zones. Big sticks can still be used to cover
geographically isolated areas, of which there are many in the U.S. -
unfortunately they waste huge amounts of spectrum in more densely
populated areas.
The article I posted this morning notes that only 17% of the TV
spectrum is actually being allocated by the FCC and used by
broadcasters. This is completely unacceptable.
What you seem to be missing is that when people tell you "big sticks
must be separated by at least x hundred miles," if they completed
their thought, they would say "in order to avoid interference
zones." If you try to use the same frequency in adjacent markets,
even with SFNs, aiming a transmit antenna AT BEST will only move
that interference zone closer or further away from one of the two
markets. It seems pretty obvious, Craig. The interference zone will
not go away. Think about it.
Correct. But it will be MUCH smaller and the more local signal will
swamp any distant signal on the same frequency.
Different subject, but yes, SFNs create more uniform coverage WHEN
you are inside the pattern. No, they don't change the interference
problem between markets using the same frequencies.
Not a different subject Bert. The same subject with some common sense
applied. With lower power levels and carefully controlled emission
patterns we gain SUBSTANTIAL spectral re-use.
Example. Replace a 150 KW big stick in Baltimore with three 50 KW
towers around the Beltway. Do you think this makes it any easier to
use the same frequency in Philadelphia?
YES.
Hardly, Craig. Chances are, you will get poorer reception in
distant cities like Elkton, and you will have created a wide
interference band between Elkton and, say, Wilmington DE. Please do
ask anyone you trust who knows these things.
Not if the transmitters are properly masked. And there will be
greater opportunity to develop separate markets between the big
markets. Delaware is an excellent example. They are covered with
interference from multiple markets today - with lower power levels
and better emission control Delaware could be a separate market.
As to nasty multipath, what do you think the separate towers of the
SFN create? SFNs only work when receivers can handle "nasty
multipath." SFNs *are* nasty multipath!
In ATSC land this is true.
Properly implemented SFNs use the energy from multiple transmitters
when signals arrive within acceptable time variations (inside the
guard band intervals). The ATSC standard does not take advantage of
this in either the high power or the new MPH modes. And the
equalizers for a DVB-T implementation are far less complex and thus
use less power in mobile/handheld devices.
Yes, and your point is?
That there are a very large number of markets in the N.E. corridor
that have managed to squeeze into the existing spectrum, and many
more sub-markets that have sub-optimal coverage because they are too
close to major markets. With SFNs it would be possible to improve
reception - especially for MHP devices - create more sub-markets, and
still recover some spectrum for broadband.
How do you think SFNs would change this? The only reason the smaller
markets can exist is that the FCC adjusts ERP and frequency use to
prevent interference. Ditto with SFNs, assuming you keep coverage as
wide in the existing markets. Which is where the 50 percent (or far
less) utilization comes in. Now, *if* you were to change TV
broadcasting to regional vs single markets, *then* I might buy your
idea that SFNs would save on spectrum. All those smaller upstate NY
markets, for instance, would not have to exist. But that also means
throwing the "localism" mantra down the toilet.
You are simply wrong about this. With SFNs we would get more channels
in more markets using less spectrum.
The reality is that a properly designed
transmission network would provide more channels
per market using less spectrum than today.
If you are trying to aggravate with vague verbiage and mere
professions of faith, the consider yourself having succeeded. I'm
staring to think that the same folks who use the phrase "the reality
is" are maybe those who also say "it's a well-known fact." <g>
Bert:
"It's a well known fact" that we disagree about this.
I would never assume that I have succeeded in changing your mind
about this subject; the reality is that you are an expert in taking
any argument and aggravating those who challenge you with vague
verbiage and professions of expertise.
Regards
Craig
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