Could that be a signal booster?

[wa2ise]

Might be, hard to tell as it's in some foreign language. But looking at the chassis picture, the power transformer looks larger than what'd I'd expect for the amount of power one tube would consume. It may be missing some parts of it.

Here in the USA we used to have UHF to VHF converter boxes so you could watch a UHF station on an older VHF only TV set. Don't know if other countries had situations like that or not. Maybe this box was one of those.