[Stuart]

The channels are divided into Muxes. The Muxes are broadcast on different frequencies. Some are more sensitive to signal loss than others. Broadband uses it's own frequencies, which, again, can be quite sensitive to signal loss.

It's also depends on the box. V+s tend to suffer a little more than other boxes with a weak signal.

If you have a low signal, you *should* contact VM. Adding an Amp (assuming you could get one) may cause more problems than it solves, and if you need to call out VM in the future, you may find that the Engineer blames any fault you have on the the changes you make to their connection, and therefore being charged for any future maintenance.

Put simply, it's not worth the risk just for the sake of a phone call and staying in to wait for the engineer.