Got a small tv in Luxembourg, no channels found (trying both SECAM and
PAL). I suppose I need an external antenna. Something cheap will likely
do the job as signals should be good in this area, but are there any
pitfalls to avoid in order to avoid a 100% useless antenna?

I understand that all TV in Europe is on UHF in analog and digital formats.
Hope you are not looking on VHF.

Frank