Furuno AT-1503 Antenna Coupler for FS-1503 SSB Radio

Check this link for photos
https://sfbay.craigslist.org/pen/ele...133647570.html
Single Sideband Radio Antenna Coupler for Furuno FS-1503 radios
Pulled from a late 80's Sport Fisher
Untested but appears to be in good condition (no signs of rust or corrosion)

That's an antenna tuner. It switches routes of the cable to lengthen or extend for matching wavelengths.

Ah, thanks for the correction.