What stations still might change Feb 17 anyways.

[Scott Fybush]

Robert S Chase wrote:
> Can somebody explain to me why the current channel 10 in Providence 
> would want to give up their analog spot to somebody else? Why wouldn't 
> they simply use it for themselves and their DTV?
> 
> I know there was something about getting an extra channel for the 
> transition but what the heck did they need it for? Why not just add the 
> DTV subcarriers and throw the switch?
> 
> Is there someplace (web site URL)  I can be referred to that has the 
> technical details and the (a logical?) rational behind all this channel 
> jumping etc?

Here's a very quick summary - it's not as simple as "adding 
subcarriers," since the DTV signal takes up a full 6 MHz RF channel, 
just as the analog signal does.

So stations can't transmit an analog signal and a digital signal at the 
same time over the same RF channel - and therefore nearly every TV 
station in the US was assigned a second RF channel a decade or so ago to 
use for its digital signal during the transition period. (And yes, it's 
really been more than a decade since the first DTV signal in Boston 
signed on, which means the DTV conversion has now lasted for fully 
one-sixth of the entire history of TV in New England...)

The TV spectrum wasn't exactly wide-open in the northeast even before 
the DTV conversion began, and trying to find room for a second channel 
for everyone created some very tight short-spacings - there are digital 
signals on channels 20 (WCVB-DT) and 30 (WBZ-DT) in Boston, co-channel 
with analog stations on those same channels in Hartford, for instance.

Within the last couple of years, stations began to get the chance to 
decide whether they'd keep their digital signals on those transitional 
RF channels, or return to their old analog channels for digital 
operation at the end of the transition.

In some cases, stations had little or no choice: because channels 52-69 
are being used for purposes other than digital TV after transition, 
stations couldn't choose to use those frequencies for post-transition 
DTV. So Boston's WLVI has to stay on DTV 41, since its old channel 56 
won't be available. (A handful of stations, like WNAC in Providence, 
were "dual out-of-core," with both digital and analog operations above 
channel 51; they had to find yet a third channel to use after 
transition. In the case of WNAC, it's taking the channel 12 allotment 
now used in analog by its sister station, WPRI; WPRI-DT will remain on 
its transitional channel, 13.)

For a variety of technical reasons, low-band VHF is considered 
undesirable for digital TV, so channels 2, 4 and 5 are all keeping their 
transitional channels (19, 30 and 20) for DTV.

High-band VHF (7-13) is considered fairly desirable for DTV, since 
stations can operate with relatively low power (saving on transmitter 
power bills) but still enjoy good coverage. Channel 7 in Boston and New 
Hampshire's 9 and 11 all chose to return to their VHF channels, though 9 
and 11 had no choice, since they're on DTV 59 and 57, respectively.

Which brings us back to Providence and channel 10. You'd think it would 
make sense for WJAR to want to move its digital from its transitional 
channel, 51, back to 10, right?

Enter one more catch: the FCC decided that interference protection after 
the transition would go to the transitional channels, not the original 
ones. And remember what I was saying about all that short-spacing in the 
northeast? WTNH, channel 8, in New Haven was assigned DTV channel 10, 
and has been uneasily coexisting there with analog 10 in Providence for 
a few years now. WTNH-DT basically *had* to go to 10 after transition to 
get out of the way of a channel 8 DTV allotment in north Jersey, and 
since it's WTNH that would get the interference protection, WJAR-DT 
would have had to use a sharply directional antenna on channel 10, 
cutting out signal to most of Rhode Island in the process.

And so WJAR decided it would be better off staying on channel 51 with 
its digital signal, where it can put out a nondirectional signal that 
covers Rhode Island better.

In the process, that opened up 10 for eventual digital use by WWDP in 
Norwell, which is on analog channel 46 and had transitional digital 52. 
I *think* WWDP could have used 46 for digital, but the low-budget 
station wanted the cheaper power bills on channel 10.

There's one more reason why some stations that could have gone back to 
VHF are choosing to stay on UHF: because the wavelengths used by UHF are 
much shorter, the UHF TV frequencies are much more suitable for mobile 
reception on things like Blackberries and iPhones and whatever comes 
after them. Some TV stations with an eye to the future believe that the 
time will come when they're using their over-the-air signal as much to 
reach mobile devices as to reach home viewers, and they believe 
(probably correctly) that being on UHF is the better bet for that purpose.

Clear as mud now?

s