Hello,
I am in the process of building a 4 element 2m yagi, centred in 146 Mhz and
will be utilising a folded dipole for the driven element.

I came across a commercial folded dipole, fed with coax that had been
threaded inside of the driven element. the coax exits through a hole in the
centre of the dipole opposite the feed point.
The coax is connected directly to the ends of the dipole, but on closer
inspection it is different coax on the feed side to the coax tail, so
obviously it is a matching transformer.

Would this be a type of a trombone balun? Assuming it is, then there would
be a 1/4 w/l of 75 ohm coax connected to the 50 ohm tail.

Are my assumptions correct?

Has anyone had any experience with this type of matching transformer? I like
the look of it as it is certainly tidier that an external 4:1 coax balun.
73
John Vk2KC