Thursday, May 8, 2008

DTV Coverage

As I have reported here and as you may have seen in our Special Report, there are pitfalls to DTV coverage. If you live in an area that gets marginal analog coverage you may not get any DTV coverage. The reason is a the "cliff effect". In the analog world when the signal gets weak you get a snowy/ghosty signal...this snowy and ghosty signal may even be received beyond our expected coverage area. In the digital world you either get a perfect signal or none at all. I guess the name implies you get the signal until you fall off the cliff.

The FCC assigned DTV specifications that were suppose to replicate a station's analog theoretically if you get the station's analog signal you should get their DTV one. The real world differs from the theoretical one.

Here is a coverage map for WWNY's analog signal. "Good" reception is expected within the circle...signals may be possible beyond the circle:
Here is the coverage off our current DTV assignment (UHF Channel 35):
After 2/17/2009 WWNY will broadcast digitally on VHF channel 7. We have made application for this coverage area (below)...and may even apply make application to increase it just a bit. This coverage should "replicate" WWNY's analog coverage:
None of us will really know if a signal can be received in a marginal area until we start broadcasting on that final assignment. We are making the move back to channel 7 and applying for the most coverage possible to make sure no one loses service from WWNY. We have generally found the coverage matches the coverage maps or in some areas exceeds it. Our best advice, now and after 2/17/2009, is to use an outdoor UHF/VHF antenna aimed at our transmitter site in Champion NY.


Anonymous said...

Those maps do look strange... did Kingston just sink into Lake Ontario?

Jim Corbin said...

These are engineering maps utilized by the FCC from their database...they only care about/regulate US coverage.

Anonymous said...

At this point, it looks like VHF will be with us for a while yet. Given that a pile of out-of-core channels have been reserved for Kingston's eventual DTV transition (which probably won't happen even one earlier than the end-August 2011 deadline) and the stations haven't even applied for those channels? I wouldn't be surprised to see the CBC affiliate wait until the last day and flash-cut on 11. Rochester also has a pair of VHF stations (10 and 13) which are returning to their original positions. I've left my existing VHF antenna in place, added a new directional UHF corner-reflector for stations (like WPBS) which will be remaining on UHF and used a signal booster with separate UHF and VHF inputs to combine the two signals. Seems to work well enough.

Anonymous said...

There were some maps posted recently at which purport to compare coverage before and after DTV transition. They are a little optimistic in that they fail to take into account what's happening just outside the B-grade coverage area (which typically is a dreadfully-snowy analogue signal but nothing watchable at all digitally due to the cliff effect). For Watertown, they predict very minor loss of WWNY coverage (based on 13.4kW VHF) in one area just east of Ogdensburg, and no loss at all for WNPI (40kW UHF). Try actually viewing WNPI from Ottawa, though, and one gets a very snowy 18 fringe signal in analogue and nothing digitally. Go to a bigger antenna or a better location and the digital signal pops into view. Are the same sort of conditions likely to occur for WWNY reception in Potsdam (which is also just outside the circle)?

It is very unfortunate that the US government waited until November '08 to authorise distributed transmission systems and until January '09 to allow applications for ordinary repeaters (broadcast translators). There's no way any of this will be built in time.

Watertown was fortunate in that all of its channels were in a 7-51 core range likely to be usable digitally. WWNY 7 should do well. There are plenty of adjacent-market 3's and 5's that are losing massive amounts of coverage area on their new digital UHF frequencies. Nonetheless, a Watertown station has a huge area to try to cover if the market's boundaries extend clear out to Massena.