TV reception problems in Sydney?

[MortonH]

Turns out the neighbours below me had a similar issue 2 weeks ago. Someone came to fix the antenna and it was sorted. I dug out an old SD set top box and it has the same issue, so certainly seems to be the antenna.

As someone who knows very little about the technology, I find it interesting that each time I retune I pick up different channels. Until now SBS was perfect, ABC and 9 were there but poor, while 7 and 10 had gone. The latest retunes today are only picking up channel 10 and its sub channels (11, etc) but none of them are watchable. Why so much variability?

[mithrandir (Andrew)]

Originally Posted by multiweb

This week-end I had to go on my roof to fix some tiles. I don't go up there very often as it's a two storey house so I made the most of it and checked the TV antenna. Prior I had done a retune. My postcode is 2168 and the website said the last retune was scheduled March 18th for the Sydney transmitter and June 8th for the Illawara transmitter. Picked up between 40 and 6o channels no problem. Then I proceeded to rotate the Antenna and my boy was checking the picture. Even rotating it out 90 degrees didn't make any difference which really surprised me. In the end I looked at other roofs and pointed the same way. So does it matter any more?
PS: I do have a powered split box, so all the TV cables are powered.

Marc, it would be interesting to know if you can see the transmitter at the top of Razorback. ABC41, TEN44, ATN47, TCN50, and SBS64. It should be on a bearing of about 214 deg true and the same distance as the Artarmon towers depending on exactly where you are in 2168.
We also have a powered splitter. As almost every room in the house has at least one TV socket the splitter is essential.

[Barrykgerdes]

Signal strength is not so important with digital TV as it was with analogue. Analogue needs a 30db S/N ratio to get a reasonable signal but theoretically a digital signal can be detected with a negative S/N ratio or a signal that is below the noise threshold using a computer process.

However to transmit a digitised TV picture requires a very high level of compression to keep it in the allocated bandwidth and this is where the problem lies. Simplified it means if one bit of information is damaged by some sort of interference the whole "frame" will not decode correctly. I expect some form of Hamming code is used to detect the integrity of the frame and if it fails the whole frame will be dropped. The loss of one frame will probably not be noticed but if the interference is severe enough to damage a high proportion of frames the picture will break up. I am not up to scratch in the digital TV as I have not been involved in TV for 30 years so my knowledge of digital TV is very basic.

Barry

[multiweb (Marc)]

Originally Posted by mithrandir

Marc, it would be interesting to know if you can see the transmitter at the top of Razorback. ABC41, TEN44, ATN47, TCN50, and SBS64. It should be on a bearing of about 214 deg true and the same distance as the Artarmon towers depending on exactly where you are in 2168.
We also have a powered splitter. As almost every room in the house has at least one TV socket the splitter is essential.

You're right Andrew. In light of your comments I had a look at the map to see where the transmitters were and it seems that when I rotated the antenna 90 degrees clockwise I was pointing at Razorback which I have a clear line of sight to. Freaky coincidence. Funny enough I've always been pointing in the direction of Artarmon and I get good signal even being in a slight depression so it's not like I have a direct view of the transmitter.