[opendtv] Re: News: Signal Trouble at Freedom Tower
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Sun, 12 Apr 2009 17:29:40 -0400
Craig Birkmaier wrote:
> yes, I am well aware of this test as well as tests doen in the '90s
> by ABC. All of these tests indicate that a small network of
> transmitters (i.e. 4-5 locations on buildings or relatively "short"
> towers would be adequate to cover the NYC metropolitan area,
Sorry, no, no, no. That's way too simplistic to be of much use.
The "small network of transmitters" you mention, in a true SFN where
they are on the same frequency and of equal size and power, can only
work reliably under certain conditions:
1. There are substantial obstacles between the towers, so that in any
given location, the signal from one tower is attenuated significantly
from the others.
2. If there are no such obstacles, the towers are close enough together
that the echo tolerance of receivers is never exceeded, even in strange
weather conditions. This is the reason why SFNs in cities like Paris and
Berlin are designed as they are.
3. You are not interested in the same area of coverage that the big
stick offered previously.
> Once again Bert, you are the ONLY person who has talked about a
> forest of small cell towers. I have consistently talked about a
> small network of medium powered transmitters (10 to 50 KW) on
> buildings and towers that need be no more than 500 ft. above
> average terrain.
Yes, you and Bob have responded this way many times before. BUT. If you
want to achieve the same coverage as you had with the big stick, and you
don't have the sort of terrain that isolates different areas from one
another, then your "small network of medium towers" will not be
reliable. UNLESS that "small network" is two towers, closely spaced. Or
one big stick assisted by small sticks (the so-called "umbrella
configuration" used in Paris), which does not meet your description.
On the other hand, if you want to expand the SFN coverage area using
small sticks, then you are FORCED to use a forest of towers, a la
Qualcomm network between Wash DC and NYC. And that forest of towers
creates large areas of interference, so that good coverage is only
possible in specific parts. In their case, within the main market areas
of Wash, Balt, Phila, and NYC, and the I-95/US-1 corridor between them.
So, not continuous coverage of suburbs and exurbs, as they would get
with big sticks. In the Qualcomm case, they had postulated 50 KW towers,
30 of them. I don't know if that's what they have built, though.
Furthermore, your claim that such SFNs would work fine, if only US TV
markets didn't spill power from one market onto the adjacent one, is
also questionable. Reason being, the ONLY way to avoid that spillage is
to create dead zones between markets. Up and down the East and West
coasts, I don't see any valid opportunity for such dead zones.
Bert
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