john Wiener wrote:

...
I've never read of using a 1:1 unun right after a 4:1 balun to minimize
RF on the outer coax.

My thinking is that the 4:1 balun acts as a voltage type and will do
nothing to ameliorate this. So, I will put some ferrite rings or snap
on ferrites just past the 4:1 balun on the coax.


Does this sound like a reasonable solution?

John
AB8O

If you use a 4:1 Ruthroff, it would be a voltage balun ... if you use a
4:1 Guanella it would be a current balun ... the 1:1 current balun is
probably more useful behind a Ruthroff ... but hey, once you have tried
all these possible combinations, you can speak from experience! grin

If going from 300 ohm to 50 ohm, perhaps you would choose a 6:1. Or,
just go with the 4:1 now and when you need some diversion, later, try
the 6:1 to see what improvments can be had and if the loss in this
design is acceptable to you ... etc.

Anyway, in this document is a 6:1 (actually 6.25:1, resulting in 312ohm
to 50 ohm) made from two 4:1 baluns (I would think Guanella ununs ...
the 4:1 can be made from two 1:1, each wound on the opposite side of
toroid core, reversing coil directions on one side. This could also be
accomplished with 4 ferrite rods ... a 1:1 balun wound on each rod, two
rods combined to make a 4:1 balun, then these "two units" combined to
construct the 6.25:1 balun ...

Regards,
JS