good signal yet no video on itv chanels help

  pastiche 14:44 06 Jan 2006

please can anyone offer me advice
I am using a artec t1 dvb usb tv with hi gain aerial I can receive all channels except ITV1,2,3 and itv news the signal meters are nearly topped out yet i only get audio and no video.
the signal is beter on these channels than on some other channels that we can receive.

any advice would be helpful

  Stuartli 16:15 06 Jan 2006

Are you talking about digital terrestial broadcasts (i.e. Freeview).

If so (and I get signals from Winter Hill) there have been periods recently when the ITV channels' MUX has been relaying lower than average signal strength.

As a result you could receive audio but no picture; however, in recent weeks, the signals have improved somewhat and the pictures can be viewed, albeit with the occasional freeze for a short time.

The problem has also been noted in other areas of the country.

  pastiche 08:32 07 Jan 2006

yes i am talking about freeview
what i can't understand is that both signal strength and snr are better on the itv channels than on otherchannels that i can receive.
i don't think that it is down to tranmission problems as it has been constant for more than 10 weeks! annd i have been in touch with the itv bods no problem according to then(this in south devon)

  Stuartli 13:36 07 Jan 2006

Then it's certainly puzzling as to why this is happening.

Perhaps doing two or three scans might do the trick as it used to work for me.

One other suggestion is that you try (just as an experiment) using Italy as your country rather than UK to see if this makes any difference (Italy uses the same criteria for digital terrestial transmissions and might be listed in the setup menu).

  dms05 10:52 08 Jan 2006

Not all Channels on Freeview use the same compression rate. BBC et al use 16QAM whereas ITV et al use a much higher compression rate of 64QAM on their Multiplex(s) so they can squeeze in more channels. I also have had problems occassionally with ITV (from Winter Hill!) - I get the sound but the picture goes.

If you are interested click here and see the technical details.

Do you loose all the Channels on a specific MUX? If you do then it's probably the QAM65 that's the problem for you.

Against all commonly accepted wisdom I placed a signal booster half way between my antenna and my Freeview box. It boosted the signal enough to restore the picture. Everyone says it shouldn't work - as you are boosting the noise as much as the signal - but it did in my case.

  pastiche 12:06 08 Jan 2006

I can not receive any video from mux2 channels
i have rescanned many times to no effect the channels are in the list and as mentioned i get good clear audio.
I have tried italian thing no diff
could there be a problem with decoding itv video signal?
Is it likely that it is something to do with my video setup?
I have had several media players installed and uninstalled could one have them set something up that causes me a prob.
sorry if they are silly questions but am starting to clutch at any idea as is realy doing my haed in

  pastiche 10:41 10 Jan 2006


  dms05 10:52 10 Jan 2006

You say your not receiving Video on Mux 2.

Are you receiving Video on Mux A (incls Five)? That's the same higher rate of compression used on Mux 2.

At least it would eliminate QAM64 compression as the problem if you are receiving Mux A.

  pastiche 10:56 10 Jan 2006

yes five is fine it is only itv1,2,3,4 itv newseverthing else is good except that somtimes the shared channels e. bbc3/cbbebies won't change without a rescn?

  dms05 11:05 10 Jan 2006

DTT uses mainly Dynamic bit rate transmission. The exception is BBC1 and ITV1 which use (high) Static bit rates so should always produce the best Quality.

Dynamic bit rates allow all the Channels on a MX to share so if one channel has lots of action then it will be given more bits to help with quality at the expense of Channels like QVC which are often completely still! The problem with this is when many channels demand high bit rates at the same time and you then see digital artifact problems.

DTT (Freeview) started with the ambition of high digital quality but as more and more channels have been squeezed on to the format the Quality has fallen. I've seen postings elsewhere which suggest many channels are now better on Analogue than on DTT. Perhaps when Analogue is switched off that will improve but the aim is to sell off the released frequencies rather than reassign to DTT.

Satellite off course has much more bandwidth to play with and Quality is easier to maintain.

  pastiche 11:14 10 Jan 2006

could it be something to do with the introduction of itv4 ?
but if this is the case why have i not heard others having same prob?
if bbc1 and itv1 are same static
bit rates why won't itv 1 at least play ball?

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