tough call. At first I thought 800MHz, but is too long for 800MHz, not
shaped right for 800MHz gain, and never saw an 800MHz with BNC connector,
so....

Its probably either a 1/4 wave UHF, or a loaded VHF..... kinda hard
to tell... depends on whats inside the "fat" part of the rubber covered
base.



Perhaps you could mount it on the output of a wattmeter with
appropriate adapter, and test a low powered VHF and then a UHF radio into
it and check the SWR.

Another idea..... take a known ham dual band HT with BNC connector,
check a constant level VHF and then a UHF signal strength with the HTs
antenna, then swap with the unknown antenna and compare again.....




Ed WB6SAT