| After a scan, no channels, or
only some channels, are found |
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Your TV antenna may need to be replaced
Television antennas are exposed to varying weather conditions and are often used as a convenient perch for birds. In coastal areas they are especially affected by salt air.
If visible from the ground, assess the condition of the antenna. Check that all elements are still in place (not bent or missing). Check that the antenna has clearance from the roof and is pointing in the direction of the TV transmission towers.
If your neighbours tell you they have good digital TV reception, compare the design and condition of your antenna with theirs.
You may need to arrange for a competent
antenna installer to assess your antenna
installation with a view to improving your
reception. Make sure he/she is equiped with
a digital TV signal strength meter.
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Your TV antenna may not be properly connected to
your HD digital receiver
Look for any connection diagrams in the installation
manual. This will provide you with the optimum connection
advice for your free to air TV viewing.
Check power connections.
Check all antenna connections are securely in place.
Especially at at wall plug and where cables connect
with the antenna socket on your HDTV or HD set top box.
And while you are at it check where cables connect to
other devices such as DVD recorders/players and games
consoles etc).
If possible, the HDTV or HD set top box must be the
first component in the receiving equipment connected
to the antenna outlet.
- Some HD Digital TV services may not have not yet
commenced in your area
Although digital TV is now available to over 90%
of Australia's population, not all towns and regions
in Australia can yet receive digital television transmissions.
In some towns and regions only some broadcasters have
commenced their HDTV services.
Infill transmitters are also deployed in many regional
areas - use ACMA's
listing of digital TV channels to check their
applicability to your situation. Download a listing of Logical Channel Numbers for digital TV services.
- The signal received may be too poor
to allow the digital receiver to find available
channels
Cables, connectors, outlets and splitters
might need replacement with high quality
components, eg, Quad Shield coaxial
cable and 'F' connectors.
You may be outside the transmission area
for digital TV, experiencing some form of
interference.
Your antenna is not providing the optimum
signal strength to the digital television
receiver. Older masthead amplifiers might
produce unacceptable levels of interference
(a carrier to noise ratio that is too high)
- replace with an amplifier with interstage
gain control and the correct maximum gain
required for good reception.
You may need to arrange for a competent
antenna installer to assess your antenna
installation with a view to improving your
reception. Make sure he/she is equipped with
a digital TV signal strength meter.
- Your old antenna may not be designed to
receive all available channels
Using the ACMA's
listing of channels - check the channels
(VHF and/or UHF channels) upon which digital
broadcasting is taking place in your area.
Your antenna must be able to receive digital
television services broadcast on all those
channels.
If your masthead amplifier has not been
designed to work on channels now used in
your area for digital television, it may
need to be replaced.
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| Picture regularly breaks up |
- The signal received may be too weak or too strong
to allow the HDTV to generate a stable picture.
The signals present at the antenna input of a receiver should conform to the following:
A. The signal strength should be between 50 dBµV and 85 dBµV. Signals below 50 dBµV may be too low to allow the receiver to receive the signal. Signals above 85 dBµV may overload the input of the receiver also causing it not to receive the signal properly.
B. The minimum Modulation Error Ratio (MER) should be greater than 25 dB dBµV. MER is a measure of the quality of the signal MERs of below 25 dBµV may too low for the receiver to decode the received signal.
Measurement of these parameters should be done at the antenna wall plate and at the digital TV (not just on the roof at the antenna) with a professional digital TV field strength meter (all good installers now carry these meters).
If signal levels are not OK, you are unlikely to have good reception unless signal strength can be improved - antenna relocation or changes to your amplifiers (masthead or distribution) may be indicated.
But remember amplifiers should only be used by your installer to provide the minimum necessary boost to signal strength - those with interstage gain control are recommended - see
below.
- Interference from impulse noise may be causing pictures
to break up and audio to drop out momentarily
Check for domestic sources of impulse noise (eg,
the use of light switches, fridges, hair dryers, air
conditioners etc.).
If present, arrange for all cables, connectors, outlets
and splitters linking the roof-top antenna and set
top box or the HDTV to be upgraded in accordance with antenna
systems for homes handbook.
The Australian Digital Testing strongly recommends
the use of quad shielded coaxial cable and type F connectors
at all times.
- A masthead amplifier may have boosted the signal
outside the receiver's "operating window",
making reception impossible
The masthead amplifier (appears as a small box on
the antenna pole within about a metre of the antenna
arms) may be able to be turned down - if your antenna
is on your roof you should arrange for an antenna
installer to perform this task.
When digital broadcasting services begin operating
in an area some masthead amplifiers (boosters) operating
at maximum output or maximum gain may need to be
turned down to avoid signal overload for the set
top box or HDTVs. This matter should be determined
by a competent antenna installer, who will be able
to adjust the amplifier for you.
Please note that performing this operation may
affect any existing analog signals, so you may need
to find a medium point between adequate analog reception
and good digital reception.
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