Building Communal Muxes

Black Hole

Black Hole

May contain traces of nut
My supported user lives in sheltered council block of flat. I did a rescan today and found some muxes I didn't recognise:

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Turns out these are the CCTV cameras within the flats: one at the entry intercom, and one in each lift. They used to be available on analogue, but now it seems DVB-T modulators have been fitted.
 
They shouldn't be using UHF 49, that's in the 700Mhz band and may cause interface with 5G mobile, or indeed may be interfered with. Barring COM7 and COM8, the 700Mhz clearance retunes use 48 max.
 
Owen Smith said:
They shouldn't be using UHF 49, that's in the 700Mhz band and may cause interface with 5G mobile, or indeed may be interfered with. Barring COM7 and COM8, the 700Mhz clearance retunes use 48 max.
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But then using 48 or lower could interfere with broadcast TV.
Perhaps 49 has been allocated to local services and 50+ are for mobile telephony.

EDIT. Now looked at BH's image ... oh :eek:
 
Owen Smith said:
They shouldn't be using UHF 49, that's in the 700Mhz band and may cause interface with 5G mobile, or indeed may be interfered with.
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My understanding of what Black Hole is describing is that the output of the CCTV cameras is being digitally modulated and distributed to the flats via the same cabling that carries the TV signal; how would that interfere with 5G?
 
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Because the likely crappy cabling in the flats will leak. The chances of it being properly to spec double screened satellite/freeview spec coax is approximately zero. Then there are the crap wall plates and crap fly leads to people's equipment to consider. Almost no-one does it properly.
 
Even better: there's a proposal to install 5G on the roof! The tenants are up in arms about it, on the fake news of health hazard (like it's any worse than 4G or 3G).
 
Owen Smith said:
Because the likely crappy cabling in the flats will leak. The chances of it being properly to spec double screened satellite/freeview spec coax is approximately zero. Then there are the crap wall plates and crap fly leads to people's equipment to consider. Almost no-one does it properly.
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But cable leakage is very low power and localised compared to a broadcast channel so interference is unlikely to be significant
 
Black Hole said:
Even better: there's a proposal to install 5G on the roof! The tenants are up in arms about it, on the fake news of health hazard (like it's any worse than 4G or 3G).
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It's actually slightly less bad(*) than 4G and 3G because power limits are a bit lower for 5G.

* Not that I agree there is any health issue with any of them.
 
In any case, who's going to care about 5G reception in a block of OAPs? And if they did, there's quite a lot of concrete to penetrate between a mid-floor flat and the roof!
 
Attitudes like this are why RF is such a mess these days. Everyone thinks it won't matter if they break the rules. Bit like covid.
 
MymsMan said:
But cable leakage is very low power and localised compared to a broadcast channel so interference is unlikely to be significant
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Agreed - if it was TV aerial amplifiers would have a problem with positive feedback.

FWIW it seems that EuroDOCSIS cable download frequencies go from 112 MHz to >858MHz, which is why VM use triple-screened cables and send you a termination plug to fit when there's no longer any equipment connected.
 
Black Hole said:
What's more, with only one lo-res service on the mux, I guess it has a very narrow spectrum.
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Probably with a little more savvy from the installers they could have combined all three cameras onto a single mux and one UHF channel but I expect because analogue required a channel per feed they just stuck with what they had before.
 
Black Hole said:
What's more, with only one lo-res service on the mux, I guess it has a very narrow spectrum.
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It will be 8MHz wide like any other mux in the UK, otherwise TVs and set top boxes wouldn't be able to tune to it. The HDR Fox T2 has 8 and 7 MHz wide mux options for reception, they're in the manual tuning menu.
 
Owen Smith said:
It will be 8MHz wide like any other mux in the UK, otherwise TVs and set top boxes wouldn't be able to tune to it. The HDR Fox T2 has 8 and 7 MHz wide mux options for reception, they're in the manual tuning menu.
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I think you've missed the point. Your quoted 8MHz is the channel spacing (and channels can vary from the nominal centre frequency without tuners being unable to find them).

The spectrum for a DVB mux is practically flat from nominal-4MHz to nominal+4MHz, because the channel is split into (IIRC) 1024 sub-channels each modulated with 1/1024th of the data stream which are then combined at the receiver into a single serial stream. One single service wouldn't need as much data as 20 or so services on a single mux, so I was simply speculating that there wouldn't need to be so many sub-channels and what sub-channels there are might be concentrated near the centre frequency.

MymsMan said:
Probably with a little more savvy from the installers they could have combined all three cameras onto a single mux and one UHF channel but I expect because analogue required a channel per feed they just stuck with what they had before.
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I think it's more a question of what modulators are available at what cost. If three single-input CCTV-to-DVB-T modulators are cheaper than one three-input modulator, that's what they'll use.
 
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