I really want to thank all the members that have replied to my subject.
Back to the subject, it is well known that oscilloscopes and spectrum analysers will depict any analog signal covered by their measuring range, and will give much more information than the TVL.
I heard about a device that is handy and portable that can give direct readings of TVL, but the side that provided me with this info is unreachable.
It seems that it is a self designed circuit.
Many thanks.