I’m off for two days, but will look it up for you when I get back to the circus. A quick-and-dirty check is to order another antenna out of stock and compare the two, measured as inner conductor of each connection to outer shield. (I am at a hub, so we have the luxury of parts and airplanes). We see a lot of upper antennas go bad, usually from delamination and water rain getting in, and before we coated the connections we had a lot of corrosion problems with connectors due to condensation in the area.
When I worked at a smaller station, I used to go visit other airline’s maintenance shacks to read their manuals, since usually their tech pubs had more information than what my airline was providing us. Granted, I couldn’t print it and take it out on the ramp to use (The Friendly Aviation Advisors would have kittens if they caught me using another airlines manuals on an airplane) but still other peoples manuals could provide information that wasn’t clear in our manuals.
Sometimes the antennas come with a shop report, which will include measurements.
(P.S. I've worked line hangar for 12 years, so I've played with this system a few times. I have been chastised for referring to it as a "fish finder")