Dontplaceliterature asked
Do you have a scholarly reference to prove that Jehovah is a combination of YHWH and Adonai?
This is a reference, don't know about scholarly, from the
Watchtower 1st August 1960 page 455.
Hebrew, like other Semitic languages, has no vowel letters, but even in early times vowel signs were used.
These vowels, according to Adams, "are indicated by ‘points' or little symbols-usually dots, resembling small periods. So when scholars of the early Modern Age began translating the Bible into English they devised what were sometimes wrong interpretations of the vowels."
The name-form Jehovah came to be when early translators took the vowels of Adonay′ and inserted them between the consonants JHVH, and then changed the original "a" to "e" to aid in pronunciation of the name.
Recent discoveries show this form of the name as early as A.D. 1270 in Raymond Martini's Pugio Fidei. So the name-form Jehovah is one of long usage.