Unsure if related but a couple of years ago I came across activity on 454.4875 which is one you have listed. After a few weeks of listening I was able to determine it was techs at Megahertz Technology doing what I suspect was range testing, that specific frequency at the time was not showing as licensed by anyone in the FCC database nor were any applications filed for it and it appears that's still the case.
No callsign was ever given by voice or morse, they didn't give much identifying information over the air and most transmissions were short with quite a bit of time between each one so it made it difficult to figure out it was them.
Never figured out where the site was but strongest signal was in downtown Dallas, I was able to receive it by handheld all the way east in Canton, south in Waxahachie, although I had a difficult time receiving it anywhere in Collin county, even on a mobile.
They stopped after a few weeks and I hadn't heard anything since. Not sure if what you've found is even related, at the time I was listening it was all conventional. I'd be curious to know.
