From eBay I got a very cheap 9:1 UNUN antenna transformer for EF (End Fed) longwire antennas. To read more about the EF antennas, please google and you find a lot of info.
The unit I tested look like this inside in a small plastic box:
The connector for the coax is BNC. This is, as you can see, a very small toroid and should not be used for other then RX or QRP.
I tested the UNUN with a 450 ohm resistor between input connector and ground. This is the result (with Fox-Delta antenna analyzer):
And connected to a 16,2 meter longwire the result is:
So, with a long wire the SWR is a little bit higher but follows the same pattern as with a 450 ohm resistor. With an antenna tuner it should be possible to tune the antenna from 40 meter band up to 10 meter band.