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Spectrum crisis

Dear editor:

Thank you to Mark Hyman for his great letter in the February issue. (You can read the letter online at The looming spectrum crisis causes one to wonder about the hundreds of megahertz of frequencies set aside for government use. If there's a spectrum crisis, why isn't this spectrum available?

Don't be silly, you say? Precisely.
Tom Norman, CPBE
Sr. engineer
Centennial, CO

Mobile DTV wake-up call

Dear editor:

There is an opportunity for content providers, networks, studios and others that may be fading away. For those who wish to partner with local broadcasters and take advantage of broader reaching audiences, the capacity to provide mobile DTV is shrinking. While it occurs to most that local station mobile DTV simulcasting makes sense, it has not yet come to pass.

The last 10 years of cultivating mobile and portable capabilities may well pass some by. That's right; the ability to provide mobile DTV may be DOA for some because broadcasters are partnering to provide access across all available platforms with all of their available bits.

Where does local mobile DTV reside in your plans for the future? For broadcasters, this is not just about “doing” mobile DTV if the answer is “Let's do it!” Rather, it's about making sure the bandwidth to do so is available. Content providers, networks, studios and others might lack clear understanding as to the bit bandwidth required to make mobile DTV possible. Consider this wake-up call an invitation to come to the table for discussion so that the local broadcaster bit capacity required is accounted for in the decisions broadcasters are making today. Think of it this way:

19.4Mb/s available (total stream capacity)

18Mb/s for HD + PSIP/overhead = 19.4Mb/s (network HD)

15Mb/s for HD + 3.5Mb/s for SD + PSIP/overhead = 19.4Mb/s (network HD and one SD subchannel)

Many may have noticed broadcasters are looking at and taking advantage of multicast opportunities. One example: Sinclair just did a deal with THECOOLTV for a subchannel in all but one market. In markets where we already have a subchannel, the bit allocation might look like:

12Mb/s for HDTV + 3Mb/s for SDTV + 3Mb/s for SDTV + PSIP/overhead = 19.4Mb/s (network HD and two SD subchannels)

Bits are valuable. With the required overhead of mobile DTV, we are looking at ~25 percent efficiency for mobile bits. That means that if we want a reasonable mobile DTV service (350kb/s video + 48kb/s audio + 2kb/s signaling = 400kb/s per service), we require 400kb/s × 4 or 1.6Mb/s per mobile DTV service.

Where will those additional bits come from? For the HDTV plus two SDTV case, maybe we upgrade encoders and squeeze another 10 percent across the three MPEG-2 video services and gain bandwidth for a single mobile DTV service. But if we are “doing” Network HD + “THIS” SD + “THECOOLTV” SD plus “some other” (just for example), we have long run out of bits. Where is the play for mobile DTV without local bits to offer? Broadcasters are looking at Sezmi and other possibilities, opportunities that may represent good economics for broadcasters. More bits are required for that! The question clearly becomes: Where do we put mobile DTV?

Here's the point: We can squeeze and squeeze and squeeze, but at some point (very nearly now!) the bits run out. If the content providers, networks, studios and others don't speak up now, broadcasters may have deals in place that preclude “doing” mobile DTV.

We need answers to the question: Where does local mobile DTV reside in your plans for the future? The time to speak up is now!
Mark A. Aitken
Director, Advanced Technology
Sinclair Broadcast Group

Generator search

Dear editor:

In your many travels and experiences, have you ever heard of the now discontinued Litton InstaGas Nitrogen generator? We purchased one in 1996, and it has failed. Litton got out of this business years ago. We want to try to fix the generator but do not have any schematics.

Maybe you could ask your readers if they know of a source for repairs or more information. Thanks!
Tom Bondurant
Director of engineering