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Forum Index : Off topic archive. : Digital TV interference - can you help?
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| domwild Guru  Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Had to buy a new TV with the cash splash money as my old one conked out. Am losing audio on digital ABC1 channel repeatedly in the evenings. If I switch back to ABC1 analogue I do not get any loss of audio. Channel 10 is completely pixelated and useless unless I also switch to analogue. Have added the supplied clamp-around ferrite ring onto the mains cable as recommended. Have one more spare ferrite ring. There is a private transformer next door, which needs its insulators washed regularly. It used to cause snow on the analogue channel and pixellation but not any more I believe. Switching the fluoro on causes the same loss of audio. Could the transformer still be the villain? Any suggestions? Thanks. Regards, Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| RossW Guru Joined: 25/02/2006 Location: AustraliaPosts: 495 |
Reducing the interference is certainly the proper cure. Often times, you can find the source with an old AM radio with a ferrite type rod internal antenna. Tune to a part of the band between stations, and go hunting the noise. You should be able to get a null (or at least minimum) interference by rotating the radio around. When the source is directly off the ends of the rod antenna, the interference will be minimum. Nulls are usually easier to pinpoint than "maximums" off the side of the antenna. If its impractical to fix the problem, a high-gain antenna may well help you. It does this in two ways: firstly, you get more of the "wanted" signal because of the directional characteristic of the antenna. Secondly, because it gets this "gain" at the expense of the other directions, it will actually reduce the amount of interference that is received. If its mains-borne, ferrites over the mains cable may help you more than ferrites over the antenna cable. |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Also, in addition to the above suggestions, DO check the coaxial antenna cable minutely for wear/ bad connections,old age, etc. I assume you Do have a coaxial antenna lead, if its still twin cable replace it with good quality 75 Ohm coaxial and also fit a balun at the antenna. I can receive a very good quality digital signal from just a small 3 element rooftop antenna which, fortunately, has line of sight to the transmitting tower some 30km away. Klaus |
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GWatPE Senior Member  Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
The signal strength meter that usually comes up in one of the setting windows will indicate low strength. You normally should replace all the coax, and even the antennae when upgrading to digital. I had to do all this on my setup when I switched to digital. Masthead amp may need to be checked as well, but not necessarily replaced. Make sure it is within 1m of the new antennae. Gordon. become more energy aware |
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| Robb Senior Member Joined: 01/08/2007 Location: AustraliaPosts: 221 |
I had one case where a set top box was generating interference across the frequency of a channel. The owner had the antenna in the roof over the TV and the rubbish from the set top box was going straight into the antenna and back into the set top box. That same box used on a properly installed antenna system with a big clean signal worked fine. The interference was coming from within the box its self as was proved by running it from a battery with no connections to any leads whatsoever with visible interference to an adjacent analogue channel. Its all about signal to noise ratio. What transmitter site are you receiving your signal from? |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Thanks for all the answers. Yes, I have a coax connection but no masthead amplifier. We live in the foothills of Perth and the transmitters are on top of the Darling Range, this means we are not line-of-sight. I shall place the second ferrite ring around the mains. Seem to get Channel 10 correctly when feeding the signal through the settop box and from the settop box via the three-lead non-coax cable (do not remember the name of that cable). Channel 10 is pixellated when the settop box is bypassed and the signal goes into the box via coax antenna cable and then out of the box via coax to the digital TV. I shall also check the signal strength as suggested and the cable. Thanks for the answers once again. Regards, Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| Robb Senior Member Joined: 01/08/2007 Location: AustraliaPosts: 221 |
Is that walliston / bickley / carmel area? This file tells you what frequency etc is used and where. Just because your watching the Ten network does not mean your looking at VHF channel 10. Now they are vacating VHF low band the ABC no longer bends over the hills like it uses to on channel 2. Its on ch 12 around here now. |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi Dom, As far I know, the digital signals are UHF. You will need a very short length of coax for this to work without a booster. Get a masthead Amp. This will improve all channels, as long as it is located as close as possible to the antennae. Gordon. become more energy aware |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Are you sure polarization is correct too? Over here, they've switched from horizontal polarization (analog TV) to vertical for digital TV (DVB-T). Also, an active antenna made a lot of difference in one case where I installed a DVB-T system. If you have a separate pre-amp, do what Gordon says and put it as close as possible to the antenna. Most DVB-T settop boxes can supply the power (+5V) for an active antenna, over the same coax ('phantom supply'); no need for extra cables. It's usually possible to turn the power on in the software menu of the DVB-T settop box. Peter. |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Peter, I too live in Perth and can confirm the TV signal polarization here remained horizontal for the digital TV channels. As I mentioned earlier, I get an excellent signal with a small 3 element rooftop antenna (its fairly new) and no masthead Amplifier. Coax length would be around 10 meters.But I can see the TV tower with binoculars from my roof top  Klaus |
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| petanque don Senior Member Joined: 02/08/2006 Location: AustraliaPosts: 212 |
When I got an LCD TV we had to upgrade the antenna. The set top box we have has a signals strength meter displayed on the screen if you press the “info” button. Digital TV is great but it seems it may not be as simple as just plugging in a set top box. Even with a new antenna it’s a lot cheaper than pay TV  |
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| Robb Senior Member Joined: 01/08/2007 Location: AustraliaPosts: 221 |
If you look at the link above you will see that they are using VHF high band (channels 6 - 12) in many areas still but not VHF low band. Masthead amps can also amplify or add noise so be very careful what you choose if you go down that route. The above link will also tell you the polarity (vertical / horizontal) they are transmitting in. |
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