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