I got the impression that the OP was planning on giving a name to an
antenna design, like "windom" or "G5RV," not a particular commercial
product. I don't think it would infringe on anyone's trademarks in that
case. He's probably concerned more about avoiding the confusion of
duplicating someone's existing name.

The trademark protects businesses like Diamond Antenna from other
people using similar names or marks to derive sales from their
presumably hard-earned reputation. If people could potentially become
confused by the name "Dim Diamond" and spend money on you, even if
you're not competing with Diamond, then Diamond are legally obligated
to take action against your use of their name.

If you are just naming the antenna design and publishing construction
notes, there is not a great likelihood of confusion; it's harder to
confuse constructing your own antenna with purchasing someone else's.
Therefore there's not much likelihood of upsetting anyone at Diamond.

Besides, some trademark holders must necessarily be less agressive. You
wouldn't expect Neil Diamond and the De Beers company to come after
you.

Oh yeah..

The number implies an engineering background.

I'm proud to say that this marketing gag doesn't work on me, and I hope
it doesn't work on many other hams. At least the name "Joey" tells you
it's from Australia and comes in a pouch.