I used to roll my own. In the very early 1980's, I had a Realistic DX-40 that used a 3/32" jack for an EXT Antenna, so I would solder a cable to that, and at the time, Radio Shack sold the 3/32" jacks at the store to buy and do that. There's a lot of portables today that use either the 1/8" (3.5mm), jack, or an RCA Phono connector, as an EXT Antenna option, so I know that adapters are out there for that. One thing to consider, does the PL-880 portable have a +3VDC voltage on the EXT Antenna connection to power a custom EXT Active Antenna, like my Sony ICF-SW100S portable did? If so, just add a .1uF capacitor as a DC block on the center conductor of the cable to the 3.5mm jack.