V+ : Cable frequencies.

[RichardCoulter]

As VM and other cable companies use closed circuit systems, are they able to use duplicate frequencies that eg DTT or satellite use, or doesn't it work like that?

[Matth]

Some frequencies, indeed a lot, for instance, the dropping of FM radio services and changing TV/FM diplexers for 5-1000Mhz isolators, was to free up additional frequencies for broadband expansion.

This is why high grade coaxial cable with excellent screening is essential to prevent egress/ingress - cheaper co-ax always skimps on braid coverage, allowing signal to leak from and into the cable.

[jb66]

Yes, my van has a sniffer and when I drive it detects leakages of rf from the virgin network and alerts the network department

[RichardCoulter]

So they do duplicate the use of frequencies, but have to ensure that there are no leaks from the system to prevent services outside of the cable system being affected?

Have I understood correctly?

Thanks.

[nodrogd]

Yep, they do. As it's a closed system, OFCOM does not regulate the frequencies they use. For that very reason the system has to be "watertight" for both ingress & egress. Even then, where Virgins networks exist close to high power terrestrial transmitters, some frequencies cannot be used.

[RichardCoulter]

Thanks, I thought that would be the case.

In this case does ingress mean the incoming signal and egress mean the return path?

[jb66]

Ingress is signal leaking into virgins network, egress is the opposite. That's why we should terminate open joints

[RichardCoulter]

Cheers