Analogue distribution of signal from Sky box

[JohnW2]

Until you 'clear a path' of any potential 4G interference then you won't really know for sure whether ch48 & 68 are as good as it gets or if they're both subject to a bit of interference. Given the cost of a 4G filter such as the one I linked in the previous post, and the fact that it blankets the whole band rather than being selective in frequency as some older filters were, and how easy one is to install, then it seems to me like an obvious step in your quest to see if this can be improved.

Indeed, that will be my first step, once the filter arrives.

Yes, I'd avoid ch48 personally, but I think that' just beating around the bush. If I was faced with this situation at a customer installation then I'd fit the 4G filter as a first step. If that wasn't available as an option then I'd run down the RF channels from 68 to 50 and not the good / bad / indifferent and choose the best from there.

As above, my next step will be the filter. In view of your personal view about ch48, do you think it would be sensible to revert to ch68 when I first try the filter? I don't particularly want to do more 'channel changing' than I have to, since each time obviously involves wandering around the house and re-tuning six TVs!

Kind Regards, John

 

[JohnW2]

If I was faced with this situation at a customer installation then I'd fit the 4G filter as a first step.

As I just wrote, that's what I'm going to do.

However, as an 'update', whilst I feel sure that I must (should have!) done this before, since it's so 'obvious', I've just tried disconnecting the aerial from the Sky box, whereupon the problem went away - i.e. the distributed Sky RF quality became fine.

If I'm thinking right, that really leaves only two likely possibilities (other than interference from some other RF source) - that the problem is resulting in interference from either 4G or some other DTV channel. Hence, the filter may well cure the problem but, if not, then I have to try 'channel hopping' to find the optimum one - does that sound about right?

Kind Regards, John

 

[winston1]

Snow on an analogue signal can be caused by two things.

1. A digital mux on the same channel. The digits appear as noise on analogue. We can probably discount this as you have tried both ch 48 and 68.
2. Too little signal. It could be that the sky box is faulty and giving too little signal mixed with noise. Note an amplifier will not help it will just give you louder signal plus noise.

Of course it could be a faulty cable from the sky box, maybe a fractured inner core. So first try a different cable. Also try connecting the sky box directly to a local TV and see what this is like.

 

[JohnW2]

Snow on an analogue signal can be caused by two things.
1. A digital mux on the same channel. The digits appear as noise on analogue. We can probably discount this as you have tried both ch 48 and 68.
2. Too little signal. It could be that the sky box is faulty and giving too little signal mixed with noise. Note an amplifier will not help it will just give you louder signal plus noise.

Indeed, amongst other things - your 'list' isn't really exhaustive. As I said, I initially suspected/assumed a variant of (2) - too little signal without an excessive amount of noise, which is why I tried adding amplifiers. However, the fact that amplifiers made things much worse would favour (1) (or, at least, interfering RF of some sort) in the presence of an adequate quality of analogue TV signal - with the main effect of the amplifier being to make even stronger the RF that was doing the interfering. However again, as you say, given that I had identical 'snow' with two different channels, one miles away from any digital signals from my local transmitter, suggests (at least, to me) that DTV signals were probably not the cause of the ';interference' - unless by 'brute force' mechanisms as mentioned below - which is why I wondered about trying an attenuator..

The most recent experiment I have reported (disconnecting the aerial from the Sky box) seems to have confirmed that it's 'something' from the aerial which is interfering with the distributed Sky analogue RF to produce the 'snow'- and if, as above, it seems fairly unlikley that it is a DTV signal (unless just by 'brute force, despite very different frequencies) that seems to leave something like 4G as the most likely suspect.

Of course it could be a faulty cable from the sky box, maybe a fractured inner core. So first try a different cable.

Needless to say, that was one of the first things I tried, with no effect - and it's inconceivable that all six cables from the distribution box have become faulty.

Also try connecting the sky box directly to a local TV and see what this is like.

That was also an early thing I did - and the picture quality was essentially identical to what it is when (as usual) the local TV' was fed from one of the outputs of the distribution box,

One of the problems is that of my memory. I can't be certain, but honestly don't recall the Sky RF signal quality being appreciably better in the distant past, but those were the days when no-one had even heard of 3G, let alone 4G/5G - so I'm less convinced than I might otherwise be that the filter is going to solve the problem. We should see fairly soon!

 

[Lucid]

However, as an 'update', whilst I feel sure that I must (should have!) done this before, since it's so 'obvious', I've just tried disconnecting the aerial from the Sky box, whereupon the problem went away - i.e. the distributed Sky RF quality became fine.

That was a good idea. It's not something I'd normally risk doing on-site.

As an installer I am always aware that if the system performance takes two steps forward but then one step back compared to troubleshooting then a customer might complain. They don't always understand the diagnostic process might involve a position that can't be replicated in use.

If I'm thinking right, that really leaves only two likely possibilities (other than interference from some other RF source) - that the problem is resulting in interference from either 4G or some other DTV channel. Hence, the filter may well cure the problem but, if not, then I have to try 'channel hopping' to find the optimum one - does that sound about right?

Kind Regards, John

Unless the cable runs have really poor shielding then I'd say the most likely in route for 4G is via the aerial. As such then, it's simply another source of RF interference.

 

[SMG]

I use a Sky HD box, I have a HDMI splitter which takes the HDMI signal to 2 tv`s, it means putting cables in, but worth it

 

[JohnW2]

That was a good idea. It's not something I'd normally risk doing on-site. ... As an installer I am always aware that if the system performance takes two steps forward but then one step back compared to troubleshooting then a customer might complain. They don't always understand the diagnostic process might involve a position that can't be replicated in use.

Yes, I can understand that - but it was nevertheless an obvious thing for me to do (for myself!).

Unless the cable runs have really poor shielding then I'd say the most likely in route for 4G is via the aerial. As such then, it's simply another source of RF interference.

Well, the above has confirmed that whatever is doing the interfering is coming out of the cable connecting the aerial to the Sky box - so, if it is 4G causing the trouble, then I would presume that putting a filter at the downstream end of that cable would cure the problem, regardless of whether the interfering signal was coming from the aerial itself or the cable, wouldn't it?

Kind Regards, John

 

[JohnW2]

I use a Sky HD box, I have a HDMI splitter which takes the HDMI signal to 2 tv`s, it means putting cables in, but worth it

If I were starting from scratch today, I certainly wouldn't use RF for the distribution.

However, for me it certainly would not be 'worth it' to change things now - particularly if I can find a way of satisfactorily addressing the issue I've been discussing. I have several very long runs of coax, in a very large house, that have been there for many years, and to replace them (neatly) with something different would involve extensive 'taking the house to pieces'!

Kind Regards, John

 

[winston1]

Snow on an analogue signal can be caused by two things.

1. A digital mux on the same channel. The digits appear as noise on analogue. We can probably discount this as you have tried both ch 48 and 68.
2. Too little signal. It could be that the sky box is faulty and giving too little signal mixed with noise. Note an amplifier will not help it will just give you louder signal plus noise.

Of course it could be a faulty cable from the sky box, maybe a fractured inner core. So first try a different cable. Also try connecting the sky box directly to a local TV and see what this is like.

OK I have just read your last post that pulling the aerial cures the fault.

So Back to 1. after all. So either a notch filter in the aerial feed on the channel you want to use or a 4G filter.

 

[JohnW2]

OK I have just read your last post that pulling the aerial cures the fault. So Back to 1. after all.

Indeed.

So either a notch filter in the aerial feed on the channel you want to use or a 4G filter.

The latter (which is what I'm going to try first) presumes that the interfering signal is 4G - or, at least, something using a similar frequency

 

[winston1]

Indeed.

The latter (which is what I'm going to try first) presumes that the interfering signal is 4G - or, at least, something using a similar frequency

A 4G filter blocks everything above ch 60. So choose a channel above 60 for your distribution.

 

[JohnW2]

A 4G filter blocks everything above ch 60. So choose a channel above 60 for your distribution.

Indeed - which is why, as I suggested, it would probably make sense for me to revert to using channel 68 (rather than the current 48) before I try the filter.

However, as I've also said, I would say think that it's not impossible (although maybe very unlikely) that a strong enough signal (from something) on a totally different frequency from the distribution channel (i.e. <ch60) to interfere 'by brute force' and that could be much more difficult to deal with - I imagine one would need to identify the source (hence frequency) of the interfering signal and then use a notch filter.

 

[Lucid]

However, as I've also said, I would say think that it's not impossible (although maybe very unlikely) that a strong enough signal (from something) on a totally different frequency from the distribution channel (i.e. <ch60) to interfere 'by brute force' and that could be much more difficult to deal with - I imagine one would need to identify the source (hence frequency) of the interfering signal and then use a notch filter.

IMO you're making a simple situation into something far more complicated than it needs to be by overthinkng it.

Sky's RF2 Out feature predates the flatscreens we use today. It was envisaged for the analogue age on SD resolution CRT TVs. Even then it was only an okay solution, but that was acceptable on a small bedroom TV at a time when a 32" widescreen or 29" 4:3 were considered decent sized TVs. We're asking quite a bit of it to stand up to the ravages of flatscreen 1080p and HD Ready upscaling.

I'd just put in the 4G filter and go from there. If you still have interference then have a look at the coax shielding on the downlead from the aerial. If it's single shielded then change to good double-shielded stuff.

 

[RandomGrinch]

I imagine one would need to identify the source (hence frequency) of the interfering signal and then use a notch filter.

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[JohnW2]

IMO you're making a simple situation into something far more complicated than it needs to be by overthinkng it.

I wouldn't really say that I am 'ovrthinking' - in terms of my issue, the only thing I am 'thinking' is that the next thing I will do will be to try the 4G filter. That will hopefully be 'the answer' but, if not, I'll move forward from there

In the meantime, my comment was a response to winston's implication that degradation of the Sky RF signal was inevitably due to something on the frequency of the RF channel being used - such that the issue could definitely be solved by a notch filter at the frequency of the Sky RF or a filter which blocked everything above ch60 (assuming that the Sky RF was >ch60) - and, as I pointed out, that is not inevitably the case.

I suppose that my comment was partially stimulated by a discussion in a sister forum just a couple of days ago (involving at least one of the same participants!), relating to the way in which very strong signals from nearby amateur radio transmitters can disturb receiving equipment, even if the frequency of the amateur transmission was very different from that being received by the receiver!

Sky's RF2 Out feature predates the flatscreens we use today. It was envisaged for the analogue age on SD resolution CRT TVs. Even then it was only an okay solution, but that was acceptable on a small bedroom TV at a time when a 32" widescreen or 29" 4:3 were considered decent sized TVs. We're asking quite a bit of it to stand up to the ravages of flatscreen 1080p and HD Ready upscaling.

I don't disagree with any of that, but I'm not sure what point you are making. If you're merely explaining that/why the Sky RF output is of limited quality then I am aware of that, but the quality of picture I can get on remote (including fairly large and modern) TVs when I disconnect the aerial from the Sky Box is, at least to my aged eyes, plenty good enough - and certainly good enough for my purpose (and a lot better than what I've been living with!)

I'd just put in the 4G filter and go from there.

As I've said, that's precisely what I'm going to do, as soon as it arrives.

If you still have interference then have a look at the coax shielding on the downlead from the aerial. If it's single shielded then change to good double-shielded stuff.

It's very old (probably 30+ years) and I strongly suspect single-shielded. However, just as with the feeds to the TV's, replacing it 'neatly' would cause considerable disruption and, if I found myself contemplating that (which I'm sure I won't) I would probably be thinking of moving to distribution other than RF!

However, don't the filters filter both the inner and outer of the feed? If they did (which is what I would have expected) then, as I said before, I don't see why it should matter whether the unwanted signal was coming from the aerial or from the cable. Am I missing something?

Kind Regards, John