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
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 08.
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 08 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 pointed
as needed to enhance the data stream reception.
Occasionally you can encounter the digital equivalent of “ghosting”
in digital reception known as “multipath”. This is when the
signal hitting the antenna is strong and equal from two different directions.
When this happens, you can get a high signal level and absolutely no
picture at all ! The two signals are causing the error-correction algorithms
in your tuner to have a migraine and they cant figure out which is the
correct signal and they just sit there and spin. Moving the antenna
even slightly can remove this problem. Other times you have to re-locate
the antenna to a different physical location on or in your home.
Now we have this HD 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 also
be taken to introduce as little noise as possible.
I have found that Channel Master products fit the bill nicely. Their
model 0068 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 a minimum of 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”
There are choices to be made about your 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.
Here are the Atlanta GA channels:
|Station Name||Station Owner||Old Analog Channel||Digital Channel||New Digital Channel||Station ID||Station Power||Network Affiliate|
|WSB||COX ENTERPRISES||02||39||2-1||ACTION NEWS 2||1000KW|
|WUVM-LP||UNA VEZ MAS||04||2.5KW||VEZ|
|WAGA||FOX TELEVISION||05||27||5-1||FOX 5||1000KW|
|WGTV||GEORGIA PUBLIC BROADCASTING||08||08||8-1||WPBS|
|8-2||WPBS – KIDS|
|8-3||WPBS – KNOWLEDGE|
|WXIA||GANNETT BORADCASTING||11||10||11-1||11 ALIVE||80KW|
|WPXA||ION MEDIA NETWORKS||14||51||14-1||ION||1000KW|
|WTBS||TIME WARNER||17||20||17-1||PEACHTREE TV||1000KW|
|WTBS-LP||PRISM BROADCASTING||26||SHOPPING CHANNEL||22.2KW||MTV|
|WPBA||ATLANTA PUBLIC SCHOOLS||30||21||30-1||WPBA||55.4KW|
|WANN-CA||PRISM BORADCASTING||32||32||32-1||CHANNEL GUIDE||18.2KW||IND|
|32-3||THIS TV||OLD MOVIES|
|32-4||PRISM TV||OLD MOVIES|
|32-5||OLDIE GOLDIE||OLDER MOVIES|
|32-7||TUFF TV||GUY MOVIES|
|WUVG||UNIVISION COMMUNICATIONS||34||48||34-1||UNIVISION I||1000KW|
|WATL||GANNETT BROADCASTING||36||25||36-1||MY ATL TV||500KW|
|WGCL||MEREDITH CORPORATION||46||19||46-1||CBS 46||1000KW|
|WATC||CAROLINA CHRISTIAN BROADCASTING||57||41||57-1||CHRISTIAN||165KW|
|WUPA||CBS CORPORATION||69||43||69-1||CW 69||1000KW|
HDTV technology link:
HDTV info from CNet (Aug 06, 2005):