Gary Sgrignoli may know as much about DTV transmission — its strengths, its weaknesses, its quirks —  as any person alive.

For nearly 30 years, he worked at Zenith Electronics (now LG Electronics) where he was deeply involved in the development and testing of the 8-VSB transmission scheme, which was ultimately adopted as the ATSC standard.

Now, a partner in the Meintel, Sgrignoli & Wallace consulting firm, Sgrignoli has emerged as a DTV transmission guru, keeping a sharp watch for problems as they arise and figuring out how to fix them.

Over the past 10 years, he has shared his wisdom with broadcast engineers through more than 85 all-day seminars on 8-VSB.

In this interview with TVNewsCheck, Sgrignoli talks about what broadcasters — and viewers — need to do to make sure viewers can find the DTV signals and keep the pictures sharp and steady.

An edited transcript:

I have been hearing lately that the DTV signal is not everything that it should be, that the reception is poor even in areas where the field strength meters are saying it should be strong. What's going on?

I have not heard a great deal of clamoring regarding this since a third of the TV stations turned off analog by Feb 17. Now we've quietly heard that there are certain areas where they're questioning whether high-VHF signals are being received properly. My concern is that there may not be enough radiated transmitter power in some cases, and that people are using rabbit ears that are not very good in other cases. Also, getting the signal indoors sometimes is a problem with high-VHF, if the only decent path to the inside is through the windows, which typically are not large enough for these high-VHF signals to pass through easily. Of course, it's worse for low-VHF signals, but there are only roughly 40 stations in the whole country that are going to end up in that band.

There are plenty of areas where people are pleased with the coverage. Unfortunately, you don't hear much from them because when people are happy, they don't bother to call in and write in and so forth. So, obviously, I believe it's slighted towards the negative side.

That said, there are three areas where problems can creep in — the transmit side, the propagation side, and then the receive side. The broadcasters are working hard on the transmit system. They're learning, they're gaining more test equipment, and they're learning how to use it and so forth, and so we've seen some really good things there.

The propagation side: Hey, you can't change the terrain or the buildings that are there. Hopefully, the broadcasters have optimized where they've placed their transmit antennas and the height of the antennas and their patterns and all that.

That leaves the receive side, which I believe is the biggest concern. That's where the industry is trying to catch up now. They have to educate the viewers on what kind of antennas they need and how to use them.

One of the problems is with "managed expectations." Viewers were told to just get a DTV set or a converter box, hook up some kind of antenna either indoors or outdoors, and assured that it would work. While that can work in some cases, it does not work all of the time. That is a problem that can only be solved with more viewer education.

Let's talk about the broadcast side first. What's going on or not going on at the transmitter site that may be causing problems? And how do you rectify it?

The broadcasters are pretty much sending out a decent VSB signal in terms of signal quality. They've learned to do linear and nonlinear pre-correction, which means to make the signal as pristine as possible before it's sent up the transmission line to the antenna. They've worked out some of the issues with average power measurement, FCC emission mask compliance, phase noise and things like that, but there may still be some issues with clock jitter.

Clock jitter?

In the early days, we saw that sometimes the transport clock going into the exciter was jittering enough that it caused the symbol clock of the 8-VSB to also jitter to the extent that it affected the receivers out in the field. This jitter can come in anywhere — from the studio to the transmitter. So that's just one thing to be careful about. The other thing is the actual symbol clock frequency. In the early days, the symbol clock frequency was sometimes not within the recommended 2.8 parts per million tolerance. Test equipment now is in place to at least inform them about the frequency tolerance of the symbol clock.

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