Antenna Test Block
To my surprise there isn't a UHF connector pigtail available.
Honestly didn't search that long. Just long enough to realize that with the box of parts from the Portable HF Radio project and my 3D printer. I could make on in less than 2 hours. Even if amazon had one and it was available in a 2-hour delivery, and I felt like spending the minimum, It would still take longer than making it.
A little Autodesk Fusion. (download SLT file
Antenna Test Box V1)
to
Then we grab a few other parts and do some very poor soldering.