[Ron Ramirez]

Any sort of insulated wire will do.

The 39-30, as with all vintage radios designed to use longwire antennas, was designed to work best with a longwire erected outdoors, 50 to 100 feet in length, as high off the ground as possible and as far away from electrical lines as possible. Such a longwire must have lightning protection by the use of a lightning arrestor.

Today, it is not always possible or practical to erect an outdoor longwire. A length of insulated wire, 20 or so feet long placed in the same room as the radio is in, is better than nothing. Be sure the far end of the wire (the end not connected to the radio) is not connected to anything and cannot be placed into a nearby electrical outlet by a child!