[opendtv] Re: Charles Rhodes on SFNs
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 25 Jun 2010 12:58:48 -0400
At 10:03 AM -0400 6/25/10, Tom Barry wrote:
How do they typically do it, lay out the areas for frequency use? Is a
simple black & white checkerboard pattern sufficient? Like:
B W B W B W ...
W B W B W B ...
B W B W B W ...
W B W B W B ...
It seems that would allow half the frequencies but maybe have too much
overlap at the corners of the checkerboard squares. Or do they need
something more like the Red/Green/Blue pixel pattern of old color tv's.
Like:
R G B R G B R G ...
B R G B R G B R ...
R G B R G B R G ...
B R G B R G B R ...
R G B R G B R G ...
That allows only 1/3 of the frequencies. Does TV even have a standard
target pattern or did it just evolve?
- Tom
The last, first.
The big cities got VHF channels - separation has typically been about
200 miles between transmitters on the same channel.
For example, channel 10 is used in Miami, the northwest side of the
Tampa. St. Pete market, and Tallahassee. The Tampa/St. Pete Channel
10 was a special drop-in, as the Riverview antenna farm to the S.E.
of Tampa was too close to the Miami transmitter (about 187 miles).
Someone tried to get ABC onto the air on a UHF channel (38 I think),
but the station went dark (the UHF tuner mandate had not yet caused
many receivers to exist.
So Rahall Communications petitioned for a drop-in on channel 10.
They got it on a 500 foot stick in New Port Richy, which is about
219 miles from the Miami antenna farm. The limited height was due to
the fact that the transmitter was in or near an approach path to
Tampa International airport. Eventually new owners were allowed to
raise the tower height.
The distance from New Port Richey to Tallahassee is about 181 miles,
but the area of potential interference is over the Gulf of Mexico and
the largely uninhabited Big Bend of Florida.
Cliff Benham knows all about this...
As for potential re-use patterns, I don't think any particular
pattern could be universally applied. In the real world terrain and
serving pockets of population density are going to be far more
important factors. Every market is gong to be different, and the use
of emission masks to limit radiation of signals into the market may
allow for closer spacing.
Regards
Craig
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