Interference on Digital TV

[Radio Tech]

Please could anyone tell me what would cause the transmitted television signal from the Sudbury transmitter to break up the picture and sound, even when the picture and sound come back the picture is jittery and the sound out of sync with the person who is speaking, the other odd thing with digital television is that if I change from the ITV channel to BBC 1 channel then back both the sound and vision is in sync.

Best wishes

Ken

[G6Tanuki]

Sounds like you have a low signal-level issue, and/or there's a defect in your equipment [old 20-yearold non-double-coax downlead from your antenna] that is allowing interference in.

After separation in the decoder the audio and video streams are buffered and if there's been interference this can lead to there being different amounts [in terms of milliseconds] of content in the audio- and video-buffers, hence the desynchronisation issue you are seeing.

I'd suggest first checking [via the onscreen display] what your signal-level is - it should be at least 90% - if not, get your antenna/downlead looked-at.

[paulsherwin]

Loss of lip sync is pretty normal when the transmission stream glitches. Both the video and audio codecs recover, but at different points in the data stream. Current DTT firmware is better at recovering than it used to be, but there can still be problems. Changing channels resets the codecs and restores lip sync.

The solution is obviously to remove the data glitches.

[Station X]

I get my TV from Sudbury and have experienced no problems.

[Radio Tech]

Hi Folks

I may have found the issue, I got my compass out to see where the aerial was actually pointing and found that it was around 10 deg out of line with Sudbury, for me the transmitter is 52 deg NW so up the ladder and shifted it, will see if it solves the problem in the evenings.

Ken

[G6Tanuki]

Here's hoping that you have found the problem.. Maybe the wind over the last few days had blown your aerial off its aim

[Sideband]

If the aerial has been there for a while, you should check for water ingress at the terminals. You should also check your aerial connection at the set. If it's a standard co-ax plug, make sure the centre connection is either soldered or crimped. We used 'F' to normal co-ax connector adaptors which gave a better connection. You can buy a cheap signal strength tester to help adjust the aerial for maximum response.

If you find the original downlead is past its best, you should consider replacing it with CT100. Avoid sharp bends and no joins. Make sure the aerial is correct for the group of channels in your area. There have been a lot of changes since analogue closed down and it might be worth checking if you need a wideband aerial or not.

[Nuvistor]

Planned maintenance Sudbury, could this make matter worse?
https://www.freeview.co.uk/corporate...ineering-works

[Sundog-]

The frequency planning for the UK and Europe do not take into account times when tropospheric conditions allow ducting of signals beyond their normal service areas.
In the UK, particularly during autumn and spring, interference from other transmitters can affect reception. If the local transmitter is transmitting at lower power, especially so.

MPG2 streams (whether native or encapsulating MPG4) can easily lose video/audio timing in these conditions.
If it annoys, simply switching to another channel and switching back should re-sync it.

If this becomes a regular problem then you should improve your aerial installation or switch to satellite reception.

[murphyv310]

Although signal strength is important signal quality has a significant bearing.
I used to have a 48ele and masthead toward Belfast and the normal channels had 48% strength and 100% signal quality with no issues and also the RTE MUX with 10% signal strength and 90% quality with no issues but at one point my local aerial was off, still had 99% strength but 15% quality and the picture was blocking with audio dropouts.
This can be due to off direction aerial, bad connections and water in the coax and of course an aerial too old and the wrong grouping.

[Andrew2]

I can't see a 10 degree error making such a difference unless your signal is marginal to begin with, or you have co-channel problems.

[murphyv310]

I do agree with Andy. 10% will make a difference with a marginal signal but if the aerial has a lot of directors then it's more prone to small directional offsets. Of course the rest of the installation needs to be in good shape. Compass settings are pretty good but you can't beat a signal strength meter.