First, I'm an absolute newbie.

I bought an old Grundig 2540 multiband receiver at an estate sale. It
works great, and I was even able to get a few shortwave stations with
the built in 12" piece of strip antenna.

So, now I want to try to make a wire antenna up in my attic. I can
probably make a 'rectangle' about 70 feet total length up there. My
question is, if I make this antenna, what is the best way to drop the
signal down into the house? I think I need to convert the long wire
into some sort of impedance match, for a coaxial feed to the room I
keep the radio in -- but on the back of the radio it has two spots for
an antenna connection: "FM" or "240 ohms"

So, what is the right way to do this? Is there such a thing as a 240
ohm balun that I'd put between the long wire and the coax?

Or something else?

Thanks a million for any help you can give me.

-Chris