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DigitalTV Interferance

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2007-2009 » Archive through 01 December, 2007 » DigitalTV Interferance « Previous Next »

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hamar
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Posted on Tuesday, 20 November, 2007 - 08:21 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

My Bios, Ex BT Engineer, Radio & TV interferance Investigations, Project engineer Digital network & much much more.
Does anyone have any experience of any interesting interference effects to digital TV?
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obiwan
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Posted on Tuesday, 20 November, 2007 - 11:55 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

???

Are you making a statement in that first line?

And are you asking for projects that cause interference to digital TV signals? Or maybe you're asking if we have seen some?
Do Not Hit The Fly That Lands On The Tigers Head.
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zeitghost
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Posted on Wednesday, 21 November, 2007 - 09:22 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Mostly the programmes...

Ah.

Sorry.

You did say "interesting"...
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boris
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Posted on Wednesday, 21 November, 2007 - 02:46 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I use a cheap Deawoo freeview box. I sometimes get digital artefacts on the TV, but I don’t know how to tell if they are caused by poor reception or by a dodgy freeview box, or both.

I have seen:

-Picture freezes for a couple of seconds.
-Picture lags the sound for a while, then the picture freezes briefly and the sound catches up, then they continue, synchronised. Sometimes it takes quite a while before they synchronise.
-Square blocks of colour appear, obscuring part of the picture and remaining in place while that part of the moving picture bleeds* back into the block, looking a little bit like a negative image for a while. The rest of the picture is normal.
-Jerky movement / low frame rate.
-Very strange looking areas on close-ups of peoples faces. Like the head moves, but the cheek and forehead don’t for a brief moment. Sort of ‘cheek lag’. This effect can be a little disturbing.
-Sometime when I change channel. The old picture will remain, frozen, while the new picture slowly bleeds* into the image, starting with large blocks, then getting smaller until the image has fully changed. The incoming image, while blocky and odd coloured, is moving.
-The whole picture (instantly) breaks up into coloured blocks and freezes, then slowly, over several seconds, the moving image bleeds* back onto the screen.

*When I say bleed. It’s like the pixels of the new (moving) image are being added (or subtracted) from the previous static image.

These effects are common, perhaps a couple of times a day. But they are short lived.
Two cannibals are eating a clown.
One says “Does this taste funny to you?”.
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zeitghost
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Posted on Wednesday, 21 November, 2007 - 04:16 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Which all goes to prove how superior Digital Terrestrial tv is...

What artefacts do you get with analogue?

Ghosting, sometimes pretty bad...

Noise if the signal strength is inadequate, but the picture will remain viewable...

I've never had picture & no sound or sound & no picture*, frozen picture*, box refuses to come on*, box refuses to change channel*, box refuses to go off*...

*until resorting to the ultimate sanction, switching the damn thing off at the mains for 10 minutes...
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hamar
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Posted on Wednesday, 21 November, 2007 - 09:10 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks Boris, that's the type of effects I'm after, most of them I would put down to your decoder however does the 'Bleed' effect cascade, almost like a pyramid, down the screen from a single point?. Obiwan, Yes and that would be rather illegal needing at least 3 racks of encoding and multiplexing equipment.
I quite agree that with all the new channels very few feature highly in my watching, I worked in a TV control center (Analogue) having to watch all the channels all the time !!! enough said.
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zeitghost
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Posted on Thursday, 22 November, 2007 - 08:33 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

And do you remember when cricket balls described an even and continuous trajectory on tv?

Instead of the jerky motion they display these days...

Does anyone else remember the early Ampex experiments with digital tv that used Octuplex recording?

That was a modified quadruplex recorder with 8 heads on the headwheel instead of 4... it did 100Mb/s to record all the information in a standard analogue signal without throwing any of it away.

Explains why DTT & DST are so ...
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terry
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Posted on Thursday, 22 November, 2007 - 10:40 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I like the way the scene of the moonlit sea comes out as lots of little squares !

Terry
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ancientbrit
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Posted on Thursday, 22 November, 2007 - 01:00 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Call me an old cynic but I wonder whether this push into digital tv has anything to do with selling off the spectrum released when analogue tv is turned off?
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boris
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Posted on Friday, 23 November, 2007 - 11:18 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Many of the brief visual affects take the form of what looks like an over-compressed JPG. EG:

Low compression (36k):
http://www.zen86415.zen.co.uk/p1.jpg

High compression (2.74k):
http://www.zen86415.zen.co.uk/p2.jpg

This can effect the whole screen or, more commonly, a portion of the screen.
Two cannibals are eating a clown.
One says “Does this taste funny to you?”.
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ancientbrit
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Posted on Friday, 23 November, 2007 - 12:20 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I was getting severe patterning on terrestial broadcasts fed from the antenna loop-through on the digi- box to the analogue Rx. Cured by making up two new RF cables using "digital" double screened coax cable. Still get the odd horizontal flash every second or so if the digi box is in standby. Fully powering it up cures this.
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hamar
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Posted on Saturday, 24 November, 2007 - 11:12 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks Boris that's a good demo of how it happens, ancientbrit the patterning could be the RF output(some have this)of your digibox on the same channel, or close to, of the one your you're watching.
Incidently you've all been watching TV digitally for 15-20 years, albeit at 140Mbt later 34M not like the 2M talking heads of today.
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ancientbrit
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Posted on Monday, 26 November, 2007 - 07:24 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks Hamar.

Yes, thanks, of course the main network distribution has been digital. Easy to forget when the focus is on the Txm side.
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zeitghost
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Posted on Monday, 26 November, 2007 - 08:49 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

It all started going wrong with sound in syncs...
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grab
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Posted on Monday, 26 November, 2007 - 02:42 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

AncientBrit, it certainly does! But the simple fact is that it takes massively more spectrum for analogue than digital, so using analogue limits your number of channels dramatically. If we want more channels, it's digital or nothing, really. (Assuming that we're not prepared to also give up radar, Bluetooth, mobile phones, GPS and other stuff already allocated to various bits of spectrum, anyway.)

Of course, someone's bound to mention the "57 channels and nothing on" problem (thanks Mr Springsteen). But still, it does mean there's better odds of someone somewhere showing an interesting repeat.

Graham.
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ancientbrit
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Posted on Monday, 26 November, 2007 - 04:48 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

>grab
I have to admit that the digital channels are an improvement, no cross colour, no visible chroma noise.
And the hard disc recorder is a treat to programme, just point and click. (Unlike the Phd you needed to programme the old VHS machines!)
The problems will start when commercial pressures dictate that the broadcasters cram in more channels.

Kind regards,

GL
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hamar
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Posted on Monday, 26 November, 2007 - 10:40 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Ah, Dual Sound in Sync, anyone remember k rating? The bandwidth issue is going to become even more interesting with HDTV gobbling up what's available & why did I only get a 80G hard drive recorder.
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ancientbrit
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Posted on Tuesday, 27 November, 2007 - 07:22 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

>Hamar
...and 50Hz tilt measurements.
And chroma/luma delay...

Regards,

GL
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zeitghost
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Posted on Tuesday, 27 November, 2007 - 08:38 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

And video recorders with 14 inch reels of 2 inch tape... real men needed to lift those onto the machine... especially a VR2000...

As Pink Floyd sang ever so long ago... "13 channels of the TV to choose from..." if it were only that few.
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ancientbrit
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Posted on Tuesday, 27 November, 2007 - 12:26 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

>zeitghost

A bit off topic but....
You'll be telling me next you remember VERA or was that before your time?

Regards,

GL
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zeitghost
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Posted on Tuesday, 27 November, 2007 - 02:19 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Ever so slightly too young...

I worked briefly with the VR2000 in the 70s.

I worked extensively with the Philips N1500 vcr...

All for QA testing of video tape.
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ancientbrit
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Posted on Tuesday, 27 November, 2007 - 02:29 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

>zeitghost

Sorry, it's the lighting in here, a bit dim. I couldn't see you properly!

Cheers,

GL
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steerpike
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Posted on Tuesday, 27 November, 2007 - 08:55 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Vera? Vera! What has become of you?
Does anybody else in here feel the way I do?
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ant
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Posted on Tuesday, 27 November, 2007 - 11:04 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hello all,

I remember VERA being announced, I was at school...

Father-in-law was a keen gardener; I scrounged some time expired 2" video tape (it curls up lengthwise so had a limited life) in order to make a cable drum. He discovered that if you pulled hard it rolled itself up lengthwise and was very proud of the fact that his tomatoes were tied up with recycled video tape!

Regards Ant
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zeitghost
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Posted on Wednesday, 28 November, 2007 - 08:41 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Really?

That explains where all the missing episodes of Dr Who went...

2" tape is heavy stuff... was it 400 video tape?
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zeitghost
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Posted on Wednesday, 28 November, 2007 - 08:42 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

"Vera? Vera! What has become of you?
Does anybody else in here feel the way I do?"

What is that track about? Weird.
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ant
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Posted on Wednesday, 28 November, 2007 - 09:36 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

No idea, Zeit, I was a sound man, firmly convinced that the pictures were better on the wireless!

Regards Ant
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zeitghost
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Posted on Wednesday, 28 November, 2007 - 12:45 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

It's one of Mr Roger Water's more obscure tracks...
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steerpike
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Posted on Wednesday, 28 November, 2007 - 01:18 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

My interpretation is that it is his recollections of the Vera Lynn songs he would have heard as a child - with sweet innocent lyrics about how triumphant England would be - in contrast to his own reality, and his father being killed at Anzio.
"The wall" seems to be somewhat autobiographical.

And I seem to have strayed somewhat from the principle topic of this thread.

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