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Television Issue - Analog


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We have a TV where the analogue signal comes from the RF output on the Sky box as it comes via a Magic eye. Unfortunately the TV seems to suffer from cross modulation as we get lines across the screen plus you can hear crackling on the TV. In the background the picture is clear. The Tv was replaced recently as we thought it was packing up.

We have taken the signal direct from the Sky box into the TV and still the same cross modulation issue. We have switched off everything in the caravan and still the same issue. We switched off the 12v leaving the 220v running and still the cross modulation. I have tried using the other RF outlet on the Sky digibox however using it makes no difference.

I am thinking that with the crackling we are hearing on the TV that there is perhaps a fault in the caravan's electrical system i. e. something arcing somewhere. The crackling is very loud and sharp. I like to think I have a reasonable knowledge of TVs and aerial systems, but this has got me stumped. It may be a faulty capacitor, diode or similar somewhere, but where. Also not something I think a dealer can trace.

 

BTW the ALDE system does not show any fluctuations or that there is an issue with the amp being drawn. Later I am going to try it on 12v only via a 12v inverter hooking up Sky digibox and TV to see if there is any difference.

 

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Two possibilities:

Could be too much signal from the Sky box. You can get a 20dB variable attenuator from Screwfix quite cheaply;

The Sky box, if using a Magic Eye, will be putting out a d. c. supply to power it and that could be upsetting the TV. It's somewhere in the menu system to turn it off - could be in the hidden engineer's menu: press the service button, then enter 0000 Select and up it will come.

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Change the RF Channel on the Sky box, tune the TV to new channel

 

https://forums. digitalspy. com/discussion/1607669/sky-hd-box-rf-output

Bailey Orion News & Information - 

 

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Two possibilities:

Could be too much signal from the Sky box. You can get a 20dB variable attenuator from Screwfix quite cheaply;

The Sky box, if using a Magic Eye, will be putting out a d. c. supply to power it and that could be upsetting the TV. It's somewhere in the menu system to turn it off - could be in the hidden engineer's menu: press the service button, then enter 0000 Select and up it will come.

I have tried the second RF output with flylead direct to TV and issue is still there.

Change the RF Channel on the Sky box, tune the TV to new channel

 

https://forums. digitalspy. com/discussion/1607669/sky-hd-box-rf-output

Thought of this but does not matter whether we are in France or in the UK. If using the status aerial, the picture is crystal clear. The other thing is that the digital signals should not interfere with an analogue signal.

I am now wondering whether the analogue tuner in the Sky+ HD digibox is faulty as with a direct feed from either RF output from the cross modulation issue is present? The digibox is about 5 years old and is a 2TB box.

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I have tried the second RF output with flylead direct to TV and issue is still there.

 

Thought of this but does not matter whether we are in France or in the UK. If using the status aerial, the picture is crystal clear. The other thing is that the digital signals should not interfere with an analogue signal.

I am now wondering whether the analogue tuner in the Sky+ HD digibox is faulty as with a direct feed from either RF output from the cross modulation issue is present? The digibox is about 5 years old and is a 2TB box.

I would echo the point about changing the RF output channel, it's normally set up in the part of the band now vacated by TV services and sold off to the phone companies for 4G.

Possibly it's your phone handshaking over the network that's causing the crackling noises.

Ssangyong Korando Sports SX / Adria Altea 472DS Eden

 

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I would echo the point about changing the RF output channel, it's normally set up in the part of the band now vacated by TV services and sold off to the phone companies for 4G.

Possibly it's your phone handshaking over the network that's causing the crackling noises.

No phone in the caravan. LOL! However took on board Wunny and your comments and went down through the channels one at a time starting at 65, then 64 which was painfully slow as had to retune each time until I reached 60 and found that cross modulation has disappeared. I had tried it earlier but skipping 5 at a time. Obviously just caught the interference somewhere. Thanks for all the help. OH is happy and that is what counts! :D

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That makes sense, the 4G phone band starts at channel 60 and goes upward from there.

Ssangyong Korando Sports SX / Adria Altea 472DS Eden

 

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That makes sense, the 4G phone band starts at channel 60 and goes upward from there.

 

Not quite. The 4G band starts <above> channel 60, but aerials and especially amps being as wide as barn doors. ..........

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The Tv was replaced recently as we thought it was packing up.

 

I can't follow why you use RF to connect Sky Box and TV

Regards, David
Peugeot 308 GT Premium, 1.5 diesel 2021

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I can't follow why you use RF to connect Sky Box and TV

I was thinking that, could you use either an hdmi or scar tissue cable, picture quality would be better then?

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Scar Tissue cable.

 

Methinks I would rather use a Scart cable :)

Graham

Unless otherwise stated all posts are my personal opinion 

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Scar Tissue cable.

Methinks I would rather use a Scart cable :)

Predictive text!!! Note to self: must check before posting

Maybe scar tissue might work better??

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Not quite. The 4G band starts <above> channel 60, but aerials and especially amps being as wide as barn doors. . . .. . .. . ..

Correct. For 800MHz/4G, it's the downlink (base station -> handset) frequencies which are immediately adjacent to digital TV. That's why interference occurs when new masts are deployed - at800, who deal with that interference, resolve by fitting a filter on TVs to get rid of everything above channel 60.

 

Conversely, in 2020 when the 700MHz band is cleared for mobile, the arrangements for that are the other way around - it's the uplink (handset -> base station) frequencies that'll be immediately adjacent to the remaining TV signals, so having a handset near a poor quality flylead won't be a good idea. Also at that stage, the TV channels will be squeezed into fewer frequencies, so the chances of finding a spare one to use for the OP's Sky application will diminish.

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I can't follow why you use RF to connect Sky Box and TV

I cannot run a HDMI cable across the floor of the caravan otherwise I will probably trip over it as the TV is in the rear of the caravan. The RF signal is fed into the existing cable in the caravan and then a flylead from the socket to the TV in the bedroom area.

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Correct. For 800MHz/4G, it's the downlink (base station -> handset) frequencies which are immediately adjacent to digital TV. That's why interference occurs when new masts are deployed - at800, who deal with that interference, resolve by fitting a filter on TVs to get rid of everything above channel 60.

 

Conversely, in 2020 when the 700MHz band is cleared for mobile, the arrangements for that are the other way around - it's the uplink (handset -> base station) frequencies that'll be immediately adjacent to the remaining TV signals, so having a handset near a poor quality flylead won't be a good idea. Also at that stage, the TV channels will be squeezed into fewer frequencies, so the chances of finding a spare one to use for the OP's Sky application will diminish.

Actually, if you think about it, if you use a 4G filter the reverse will be true.

On channels above 60 the filter will remote all the 4G traffic leaving them free for what is effectively closed circuit transmission by cable.

Ssangyong Korando Sports SX / Adria Altea 472DS Eden

 

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Correct. For 800MHz/4G, it's the downlink (base station -> handset) frequencies which are immediately adjacent to digital TV. That's why interference occurs when new masts are deployed - at800, who deal with that interference, resolve by fitting a filter on TVs to get rid of everything above channel 60.

 

Conversely, in 2020 when the 700MHz band is cleared for mobile, the arrangements for that are the other way around - it's the uplink (handset -> base station) frequencies that'll be immediately adjacent to the remaining TV signals, so having a handset near a poor quality flylead won't be a good idea. Also at that stage, the TV channels will be squeezed into fewer frequencies, so the chances of finding a spare one to use for the OP's Sky application will diminish.

 

 

Nope. You can work out the centre frequency of a channel from

(Chan No x 8) + 306. Therefore 60x8=480+306=786.

The channel is nominally 8MHz wide so the top end of channel 60 is 790MHz and the 4G band starts at 791MHz, so I stick by what I said - the 4G/LTE 800MHz band is <above> channel 60.

 

If there is any sense being applied the channels in use will have started from the top end and be working downwards as more come into use. There is no way a simple filter could pass 790MHz and block 791MHz, so if they want to avoid upsetting people they should be using the higher channels first.

 

The problem is more often that the aerial amp and the input circuits of the TV are as wide as a barn door - they were/are designed to work up to and including channel 68 after all.

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Actually, if you think about it, if you use a 4G filter the reverse will be true.

On channels above 60 the filter will remote all the 4G traffic leaving them free for what is effectively closed circuit transmission by cable.

That would be true if many TV aerial fly leads didn't act as pretty good antennas to pick up the LTE/4G signals. The theory's good though, depending on the quality of the lead.

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Nope. You can work out the centre frequency of a channel from

(Chan No x 8) + 306. Therefore 60x8=480+306=786.

The channel is nominally 8MHz wide so the top end of channel 60 is 790MHz and the 4G band starts at 791MHz, so I stick by what I said - the 4G/LTE 800MHz band is <above> channel 60.

 

If there is any sense being applied the channels in use will have started from the top end and be working downwards as more come into use. There is no way a simple filter could pass 790MHz and block 791MHz, so if they want to avoid upsetting people they should be using the higher channels first.

 

The problem is more often that the aerial amp and the input circuits of the TV are as wide as a barn door - they were/are designed to work up to and including channel 68 after all.

Not sure why you're saying "nope" - I was agreeing with you?

 

On the 4G frequency usage, it can't be phased because each operator has a particular frequency block that they paid for. Three is immediately adjacent to TV, and they've only got 5MHz, which is (was) the minimum supported LTE/4G bandwidth - it wouldn't be fair to say they can't rollout until after everyone else. The filters are fairly good though - they're spec'd basically not to attenuate channel 60 but insert at least 15dB loss into the Three frequencies.

 

That said, your "barn door" thesis is correct - the evidence is that poor TV receivers are overloaded by any 4G signals. .. there's no more interference when looking down the (adjacent) Three base stations than there are with the mobile operators that are higher up the 800MHz band.

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Just for a laugh. When we got home and fitted the Sky box back in place, we were wondering why we had no signal in the bedroom at home until I remembered that I had altered the channel to 60. OH happy again! LOL! :D

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