Hi

I am trying to build a broadband UNUN 9:1 from 1.8 mhz to 30mhz. I
have had no luck.

The first one the that I built, I used #67 material trifila wound 8
or nine turns. This one works
from 80 through 15 meters.

I also tried a Quadrifilar winding on a #67 and #61 core as multi
impedance transformer, still
narrow band with bad or high VSWR from 10mhz to 30mhz.

I tried another one with #61 material and did not have much success.

I then tried a auto transformer type primary 9 turns secondary 44
turns using a Amidon 61 core.
This produced a nice low frequency UNUN .5 mhz to 10 mhz.

The question is simply how do I build a broadband UNUN or
Autotransformer from 1.8mhz to 30mhz and what core do I use? I am
coming to the conclusion that these auto transformers or high
impedance UNUN's are narrow band devices?

I am playing around with a terminated T2FD type antenna trying
different impedances, 450,600,800 and 1000 ohms termination resistors.

Bob