HDTV RECEPTION PRODUCTS

As in the world of analog off-air reception, the reception of HDTV off-air signals can be challenging and frustrating. The content of the HDTV signal is very different but you are still trying to receive a carrier wave with an antenna made of resonant rods and wires. If you haven't already done so, please go back to our Off-Air antenna page and read through the reception basics.

To produce an HDTV picture, broadcasters send digital data over a carrier (channel). The decoder (tuner) in your TV set or in your outboard satellite receiver or stand-alone HDTV decoder, strips off the carrier and sends the data stream into a buffer called a cache. When the cache fills, the data is displayed as picture and sound on your TV.

This is much like watching news or music videos on your home or office computer. The data flows in and the cache fills and when there is enough information to begin streaming the data onto your screen, you see a picture.

If the carrier drops out for an entended period of time, the cache will play out the data till it is exhausted. This causes your picture to "freeze" until the cache is re-filled at which point, your picture resumes.

It is the job of your antenna to receive the carrier and provide this reception continuously without lengthy drop-outs. It is better to have a steady weak signal than a strong intermittent one.

Analog signals can be on any channel from 2-69, while the majority of HDTV channels are in the UHF(ultra-high frequency) band. There are, of course, exceptions to this rule. In Atlanta, the VHF (very high frequency) channel 10 is used by NBC for their channel 11 HDTV broadcast. Public Broadcasting channel 08 occupies VHF channel 12.

The VHF channels of 02 to 13 are able to travel farther with less transmitting power than do UHF channels by their very nature. UHF channels tend to be more affected by terrain and foliage than do the VHF channels. Most antennas installed on homes tend to be the broadband type which means they will collect both the VHF and the UHF channels. But due to the nature of the UHF signal, broadband antennas tend to have less optimal UHF reception characteristics. It is difficult to receive both UHF and VHF with equal emphasis especially where transmitters are located in even slightly different directions.

Most broadband antennas are rated by range, gain and beam-width. Range is how far away a station can be to be received, gain is the ability to collect this signal and beam-width is the directional ability of the antenna. Most broadband antennas use a log-periodic arrangement of elements which increases gain and directivity but provides a narrow beam-width. The length of the antenna from front to back is a good relative indicator of beam-width, with the longer antenna looking more directly ahead while a shorter antenna will look ahead with a wider view.

Of importance to HDTV reception is the ability to provide great amounts of passive (non-amplified) gain and a wide beam-width. We have found that the Channel Master 4228HD 8-bay UHF antenna has superior gain with almost 120 degrees of beam-width. It also allows for reception of the out-of-band signals of channel 10 and 12 which carries Atlanta channels 11 and 08 respectively. It has worked in locations close-in to the transmitters and at a distance of up to 50 miles from the transmitters!

HDTV also allow for multiple antennas to be coupled together. In the analog world, if you couple antennas together there is a strong propensity for severe ghosting. Since HDTA signals are digital, the error-correcting algorythms in the decoder/tuner has all but made ghosting a thing of the past. Several antennas can be joing and pointedd as needed to enhance the data stream reception.

Now we have this Channel Master antenna up on a pole above the house. We have our balun (matching transformer) attached and we have run a coaxial cable down from the roof to our HDTV tuner. We turn on the display and the tuner and we hit the menu and look for the option to scan for digital channels. We get all the local channels but when we tune to them, they "freeze" up and the motion is stop---start----stop, or we may just get a few lines of the picture every few seconds.

Back up to the roof for a little re-aiming and we just can't get the signal to be constant enough or strong enough to pull in "watchable" HDTV. Depending on the cause, be it distance, a hill or houses blocking our direct line to the transmitters or even cable length, we need a way to garner more signal. This is where we start to consider our options.

We could raise the antenna. This would help us to try to escape any hills or other obstructions between our antenna and the transmitter. This has it's limits though. Not all folks out there want their house to look like a NASA outpost with guy wires and antennas way up in the air. It might not be feasible for a number of reasons.

The job here is to do our best without amplifiers before we even consider them. An analogy would be a race car. If the car wont run, you don't put a blower on it it make it go faster. You don't amplify nothing and come out with something. This is especially true in the digital world. The addition of an amplifier introduces some small amount of noise into the mix. The noise is in essence, a digital critter. Your tuner can't tell the dots and dashes of the digital signal from the chaotic dots and dashes of the amplifier induced noise. So amplifiers should be chosen not only for their ability to increase the signal but care must be taken to introduce as little noise as possible.

I have found that Channel Master products fit the bill nicely. Their model 0064 and 7777 pre-amps offer superior characteristics and work well in most HDTV installations. They are rugged in terms of weather and lightning resistance and they have 20dB gain and low noise.

If your antenna can pick up several channels from one direction but must be re-aimed to receive other channels from a different driection, then you may have a case for the installation of a rotator. This will allow you to remotely move your antenna to the position where signals are optimized for the desired channel. Sometimes, where the antenna is located behind a hill from a direct line to the transmitters, you may fair better by rotating the antenna away from the primary signal and catching a "bounce" signal from a hill behind you.

Rotators are less desirable in homes where there are multiple TV sets. If one person wants a channel transmitting from the East and another family member wants a channel transmitted from the West, negotiations will commence and someone will not get to watch their programming. This is precisely why it is best, if at all possible, to have an antenna system that can be pointed in one direction and capture the desired channels.

Rotators add to the cost of the installation and require additional wiring fromt he roof to the primary TV location. While they have long life-spans, they can develop problems and do require an additional step when selecting your desired viewing channel.

You shouldn't automatically assume that you can get by with a simple set of rabbit ears because you live close to the transmitters. Some people who, by the luck of the draw, live in an optimal reception area may do very good with just a rabbit ear antenna. But it is often more difficult to receive HDTV signals in the urban environment due to reflected signals, directional issues and tuner overload.

There are some devices out there that look like boomerangs, bun-warmers, shark fins - some with and without built-in amplifiers. While some folks may get decent results, many of these new "digital" contraptions you see on the market for ridiculous prices approaching $300 are actually no more than rabbit ear type antennas in weatherproof cases. If you purchase one of these and get decent reception, you are (in my view) in the minority.

I have seen ads for gadgets that plug into the electrical wall outlet and deliver, "stunning HDTV reception". HOGWASH. The idea is that electric lines run all over God's creation and by tapping into them you can extract a usable TV reception signal. Aside from the possibility that they could be dangerous, the units I have seen failed miserably and deliver colored snow at best and waste money. The one thing you can count on when you use your electric wires as an antenna is NOISE and lots of it.

In the early stages of HDTV, the broadcasters were still heavily tinkering with their systems. There are chat rooms where you can chime and add your comments to their threads. Sometimes the information found in these chat rooms can be invaluable. I have heard stories about how channels transmit signals that are incompatible with certain HDTV receivers; or where the guide is on the wrong date, or the sound is "weird" or non-existant.

Most of this has been worked out with a few notable exceptions. In the Atlanta area the UHF channel 69 broadcasts it's HDTV signal on UHF channel 43. Most HDTV tuners out there do not display this as channel 69-1 but as channel 43-1. This is due to an glitch in the data stream and should be worked out over time. (Most of the new stand-alone decoders now handle channel 69 and convert to a display of 69-1 and not 43-1...NOV08)

There are choices to be made about TV set, set-top or built-in decoder, or even choices between satellite HDTV, cable HDTV or off-air antenna HDTV reception. And all of these choices will be different for you in different parts of the country.

Depending on your satellite or cable TV carrier, you may not get all of the local channel in HDTV.

HDTV technology link:

HDTV Reception