Monday, June 23, 2008

The Problem Is Not In Your Set!

I have been getting calls and emails recently from several people all with the same question. It seems that they have either purchased a new DTV set or have connected a DTV converter to their old analog set and have experienced a strange phenomenon. They are getting great digital reception from all the local stations except Channel 9, WCPO DT.

Now let’s be clear. These are people who do not subscribe to cable or a satellite service. Instead, they rely on over-the-air reception to watch TV.

There is a very simple answer to this conundrum. The problem is not in their TV set. The problem is on top of the TV set or on the roof. It is very likely the antenna.

Back in the 1990s the FCC assigned new channels for DTV to all existing full-power broadcasters. In most cases these new channels were in the UHF band, i.e. Channel 14 – 68. For example CET received DTV Channel 34, WLW got Channel 35. Both are in the UHF band. WCPO got VHF Channel 10. Therein is the problem.

While you may not know it, there are significant differences in the design of antennas used for picking up UHF channels from those designed to pick up VHF channels. I won’t go into the physics. Take my word for it. So if you have a UHF antenna, either set top or roof top, and it is a “UHF only” model, it will not pick up the VHF signal from Channel 10, WCPO.

By the way, don’t let these numbers confuse you. In order to keep it simple, all digital TVs and converter boxes display the old channel analog numbers so the consumers don’t have to get used to a new numbering system. When you watch CET’s digital channel, which as I said above is really channel 34, the TV channel indicator will display good old Channel 48.

OK back to the problem at hand. I did an experiment. I live on a very high ridge just north of Harrison. On a clear day I can see some of the TV towers in downtown Cincinnati from my front window. I connected a UHF/VHF antenna to a DTV receiver and got a good picture from Channel 9 DT. I switched to a “UHF only” antenna. I got nothing.

You might ask why now? You may be using the same antenna that you used for getting analog Channel 9. The UHF antenna worked OK.

Digital signals are different in that they are either perfect or non existent. It is called the “cliff effect.” With analog signals we all have experienced a TV signal that is snowy. We put up with it until it is no longer viewable. A digital signal will never be snowy. If the TV set’s circuitry determines that it can not provide a perfect picture, it will just go to black. I think that is what is happening with our callers’ sets.

The solution is to get an antenna that is designed for both UHF and VHF. That should fix the problem. Some set top antennas have amplifiers. This can help as well. Be sure that the amplifier can be switched off. There are some instances when too much signal can cause problems as well. That’s another column.

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