VK2KC Gmail Inscribed thus:

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?

More or less :-)

I've tended to prefer a gamma match... its far more flexible in terms
of matching and does the balanced to unbalanced conversion as well.

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

73's
--
Best Regards:
Baron.