What is TV interference?
TV interference occurs when an unwanted signal or noise competes with the signal from a broadcast station and affects TV reception such that it becomes difficult to hear the sound or see the picture.
What is external interference?
The interference is external if the source is not in the viewer’s premises, or beyond the viewer’s ability to control.
What is fortuitous reception?
Sometimes it is possible to receive TV signal from a distant transmitter that is not planned for a particular area. These fortuitous television signals are more likely to experience reception difficulties due to the unreliable nature of weaker, more distant signals. They are also far more susceptible to interference from nearby sources.
The ACMA do not investigate interference issues to fortuitous reception.
How do I know my client’s TV reception problem is due to interference?
The majority of reception problems are not due to interference, and caused by the effect of anyone or the combination of problems with coverage, antenna installation and TV receiver. A web tool mySwitch will enable you to find coverage information such as the predicted level of coverage, available channels and antenna set-up information. Measuring both the level and quality of the signal at different places (antenna, masthead, splitters etc) on the antenna installation, allows you to establish the condition of the antenna installation. A signal with good strength and poor quality may be an indication for interference.
The antenna and distribution system
What is a good antenna installation?
Antenna installation is a vital part of television reception. In designing or upgrading a system, it is necessary to consider the level and quality of the available signal as well as level margins. These margins determine the robustness of the TV reception and how close the reception is to the digital cliff. An allowance for interference, such as impulse noise from power lines and fading of the signal, should also be provided. Quad-shield cables and fly leads minimise the induction of impulse noise at other points beyond the antenna.
When replacing antennas, do not assume the best location is an existing location/pole. The environment may have been changed with grown up trees and new buildings. A fresh site survey for good signal strength and quality signal may be necessary.
Have you got the numbers?
What is important? Strength or quality of the signal
The quality of TV reception depends on both the strength and quality of the received signal. For good TV reception, the desired signal level at wall plates is around 54 dBµV. Signal levels below 45 dBµV and above 80 dBµV is not suitable for TV reception. Signals with good strength and poor quality may be an indication for interference.
What is CBER, VBER & MER?
CBER, VBER and MER give an indication of the quality of the signal provided to the receiver. A TV receiver is able to identify and correct certain amounts of error in the transmission channel. In the TV receiver, error correction takes place in two distinct stages called Viterbi (or ‘outer’) and Reed Solomon (or ‘inner’) correction. The bit error rate (BER) before Viterbi correction stage is known as CBER. It is also known as ‘pre Viterbi BER’, raw BER’ or channel BER. CBER indicates errors present before any correction has taken place in the TV, set-top box or test instrument. Therefore, CBER is a very important part in digital TV measurements and it should be better than 2E-2 (2 errors in every 100 bits of data) for good quality TV reception.
The bit error rate after the Viterbi correction is known as VBER or post Viterbi. It should be better than 2E-4 (2 errors in every 10 000 bits of data).
Modulation Error Ratio (MER) is a measure of the sum of all interference effects occurring on the transmission channel. For good quality TV reception preferred MER is at least 25 dB.
What are the common sources of interference?
Masthead amplifiers, LED lights, power lines, street lights, and electric fences.
How do masthead amplifiers cause interference?
Masthead amplifiers do cause interference if they are not installed properly or in faulty conditions. They should only be used if absolutely necessary, and should be checked to ensure correct configuration and suitability to the particular area of TV reception. The gain of the amplifier must correctly be set for the required level. Overload (high level signal causes the amplifier to distort), mixing (multiple RF signals combine within the masthead amplifier) and oscillation (a result of signal feedback) are the main causes for interference. RF signals from an oscillating masthead amplifier can cause interference to many households in a given area. It may cause interference to other radiocommunications services such as mobile phones.
Read more masthead amplifiers.
Getting help with interference
How do I seek assistance from the ACMA to resolve interference?
The ACMA provides assistance to diagnose reception problems when TV reception is affected by external interference, not power line interference. After completing necessary tests, if you are of opinion that the problem is due to external interference, you can seek assistance by submitting R202 form to the ACMA. Consideration for your request for interference investigation will depend on the information you have provided on the form, particularly section B. The ACMA may contact you to get further information and in some situations your presence is also required to resolve your client’s reception problem.
Ensure that you provide the signal levels, CBER, VBER and MER for all channels as measured at the wall outlet.
During the investigation, the ACMA will keep you informed about the progress of the investigation. The ACMA will inform you of the outcome of the investigation, however it may not be able to identify individuals who own or operate interference sources, or disclose the details of any compliance action taken due to privacy obligations.