[opendtv] Re: Demand for free DTV rising in Australia

Dale Kelly wrote:

> That would indeed be an interesting exercise. Since COFDM
> worked at virtually every urban location using the first
> gen. receivers it would be an instructive demo without its
> retesting, assuming the same Sinclair transmission system
> could be used.

The Sinclair test results I was referring to, and results also from Oak
Technology, are available here:

http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/reports/dtvr
eprt.doc

(You'll probably have to repair the split URL.)

The FCC report talks about the Baltimore tests starting in page 10.

Here are two Sinclair results that would probably benefit from a
re-test:

"Both locations visited during the demonstration were within about eight
miles of the WBFF-TV transmitter.  The first location was on Lombard
Street.  Measurements were taken on the sidewalk at street-level.  At
this location, both COFDM and 8-VSB reception were achieved using the
bow-tie antenna.  However, reception using the COFDM system was easier
to acquire and was maintained over a full 360 rotation of the antenna.
8-VSB reception at this location was achieved over two arcs of about 60
degrees each, or about 120 degrees.  In addition, the antenna had to be
rotated more slowly and carefully for 8-VSB reception.  The second
location visited was an 11th floor apartment located in the Baltimore
Harbor area on Lee Street.  This location faced away from the
transmitter site so that only reflected signals could be received.  At
this location, only COFDM reception was achieved with the bow-tie
antenna.  8-VSB reception was only possible by placing the reflector
type antenna in direct contact with the aluminum window frame.  Those in
attendance postulated that this effectively permitted the entire window
frame and surface to become part of the receiving system."

From Ken's description of his reception in Manhattan, and from many
other similar reports we have seen over the years, I would have to
conclude that such a re-test would be closer to parity now.

Further on, the FCC report says:

"On September 24, 1999, Sinclair presented a report of the results of
its Baltimore reception tests to the IEEE Broadcast Symposium in
Washington, D.C.   The report documents reception results at 40 sites in
the Baltimore area.   Sinclair indicates that approximately
three-quarters of these sites were located within the "near field,"
i.e., less than 30 miles, of the WBFF-TV transmitting antenna.  It
reports that 8-VSB reception was successful at 10 of 31 sites with a
Panasonic receiver and at 12 sites of 31 sites with a Pioneer receiver.
For COFDM, it reports successful reception at all 31 sites with a Nokia
receiver and at 21 of 25 sites with an NDS receiver. Sinclair also
presents 'ease of reception' data showing the range in degrees of
antenna orientation at which reception was achieved.  The Sinclair data
indicates that COFDM was less sensitive to antenna orientation than
8-VSB.  Sinclair indicates that it was not possible to receive 8-VSB
signals at locations with 'spectrum deviations' in excess of 15 dB from
a signal with 'nominal reception' characteristics.  It further indicates
that COFDM reception was possible with spectrum deviations of up to 25
dB.  Sinclair also states that 8-VSB, as compared to COFDM, was quite
intolerant to dynamic multipath conditions.

"Sinclair indicates that the purpose of its 'far field,' i.e., beyond 30
miles, testing was to try to determine if a meaningful difference in
performance could be observed due to the differences between 8-VAB and
COFDM in threshold carrier-to-noise (C/N) ratio needed for acquisition
of service.  It states that while there is a 4 dB difference in the
theoretical C/N performance between of the two systems in favor of
8-VSB, the average daily calibration threshold difference between the
8-VSB and COFDM receivers was 3.28 dB and that in the field this
difference shrank to 2 dB.  Sinclair suggests that this may be due to
the effect of real world impairments that add to the theoretical
'gaussian' channel values."

Again, I think it would be instructive to revisit at least some of these
other locations, just to see if what now applies to 8-VSB is more
similar to COFDM than it was then. My bet is that this is the case.
Also, in the Oak Technology part of the report, everyone was saying that
it should be possible to make 8-VSB work in all of the sites.

> I don't have the original documentation from Baltimore so
> don't know if the original channel (45?) is operating as a
> DTV at that location and at about the same power.

Channel 46 actual, now at 550 KW (the FCC still shows "construction
permit," but Mark Aitken said power was increased). For near field
tests, where there was plenty of power available regardless, maybe the
higher power now doesn't change things appreciably. For the far field
tests, obviously that's a problem. I don't see any Baltimore digital
transmitters at 45 KW ERP anymore.

Bert
 
 
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