Residents of Wollongong, and Sydney's southern and hills districts who own VCRs are being warned to take precautions to protect the quality of their analogue television. The move would avoid problems that affected some Newcastle residents when digital broadcasting commenced in the region 12 months ago.
The ABC and SBS have already started conducting test transmission in the region with commercial networks slated to begin broadcasting to the Illawarra next February.
According to Keith Jones, chairman of television broadcasting standards body CT2, the reception problems relate to the sharing of ultra high radio frequency (UHF) bandwidths used by VCRs and digital television broadcasters.
It is common for VCRs to send vision to a TV via radio frequency on a co-axial cable but if there is a free-to-air signal competing for the same frequency it can interfere with the TV picture.
Each television network has been allocated a UHF channel to transmit digital signal. In some regional areas the channel may match that used by a viewer's VCR, causing interference lines and patterns on the TV.
The problem mainly affects regional areas where broadcasters have been allocated channels that are very similar to those used commonly by VCR makers.
Viewers should be on the look out for vertical or diagonal lines passing through their picture at a regular tempo or -beat".
In most cases, if a problem does occur, viewers should be able to circumvent it easily said Jones.
-Most newer VCRs let you select virtually any channel in the VHF range...older VCRs maybe restricted to a couple [of channels] and very old ones may actually be on zero and one," he said.
Alternatively, he said, viewers can by pass the problem altogether by using audio-visual ports on their link their Television and VCRs.
Jones said the problems have been common knowledge since digital broadcasting began and that the responsibility for informing the public of the signal interference problems lies with broadcasters; however he couldn't say how successful the campaigns had been.
-I would guess that until a viewer actually gets a problem they're probably not going to be terribly aware of it or probably being terribly receptive to listening to the information or finding out about it," said Jones.
The problem took Newcastle users by surpris when digital test transmission commenced there last April. Viewer complaints sparked some concern in the media regarding digital television.
This time commercial broadcasters aren't taking any chances. Digital Broadcasting Australia (DBA) late last week informed retailers that commercial networks had begun airing public bulletins in Sydney, Central Coast, Wollongong and Newcastle recommending that viewers use their audio-visual outputs to link their TVs to their VCRs.
DBA said the announcements are being made in anticipation of the launch of the commencement of digital broadcasting in Wollongong next February.
The problem is not new. Early VCRs used channel zero and one for transmitting signals to TV sets but manufacturers were forced to stop the practice to make way for SBS when it began broadcasting on UHF channel O.
Jones said that some electronics manufacturers have already started changing the factory default frequencies of their VCRs to 69.
Since the advent of Digital TV to the Illawarra
there ha been a constant strength seven hash on
the HF bands from 4 Mhz to 12 MHz. Has anybody
any idea how this is being generated.