I think it came with the Tecsun R9700DX, but I cant remember for sure.

It's a 30' wire black insulated wire with a plastic alligator clip on one
end.
I've never used it much.

One evening recently, I decided to open the window, and drop the wire out of
of the small space between the screen and the window frame. I clipped the
end to a variety of portable receivers.

Sony-7600GR
Grundig-YB-400
RS DX-398
RS DX-202
Kaito KA-1103
Kaito KA-1107
Tecsun R-9700DX
Tecsun-PL-230

The results were impressive. It gave the portables stronger receive, better
clarity, and improved sensitivity.

The 1107 strugged with selectivity, but the rest performed well.
I have used that a few more times, when the weather is cool enough to open
the window, and turn off the A/C.
I'm anxious to use it this fall.