Larsen PO UHF antenna
From Wildsong
This came with the Radio Modems.
I have a paper doc for it!
It looks like it's a mobile UHF omni with a PL-259 connector and a Larsen base station kit to turn it into a base antenna.
The lower section is about 9 1/2" and the radio modems are 420 MHz so it is probably the PO 420 set up for 420-425 MHz