Found a SO-239 to 3.5mm mono phone plug adapter.

I just found and have ordered a couple of UHF Female to 3.5mm plug adapters. I am going to use one of them to hook a Tecsun PL880 portable receiver that uses a mono 3.5mm jack for the external antenna to one of my dipoles. I know the Sangean use this setup and I think the Sony ICF7600 does as well. I am going to make an adapter so I can hook up to my Zenith Trans-Oceanic, and the RCA Victor Strato-Worlds to my outside antennas. They are only available on eBay at CQ Radio Supply. A great outfit he has have saved a great deal of money. I purchased a quality "C" connector, which is an "N" connector with a bayonet mount like a BNC, and a couple of Twinax connectors, for my R390A. The "C" connector was $18.50, the Amphenol "C" connector at Digikey is $126.55. I also purchased a "C" to BNC adapter for $25.95