Hi
I’ve recently got a new Volvo FH 12. It comes with the fittings for a flat screen TV but when I fitted it I can’t get a digital signal the majority of the time.
It does say in the manual that the TV has to push 5amp to the fitted antenna for it to work so this could be the problem.
Is there anything I can use to boost the power to the antenna?
I gave up with the fitted ariel in mine and found using my own was a lot better.
I find Freeview is a pain in the arse in general. I stay at the same place in High Wycombe in the same spot where possible. Some days I get every channel. Other days I get none. I reckon the weather plays a part. 
Or how close other trucks are to your aerial. I will often park up, tune in and get all the freeview channels and then another truck will park alongside and I will lose 75% of the coverage! I don’t think there’s much you can do when just using a 24v in cab aerial booster.
I think they need a 5 amp supply to work, some tv’s have the option to turn it on in the menu if not you can buy a booster. We got ours from lymm luckily one of our drivers is a dab hand with this stuff