Greg wrote:
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

Type 43 or a 70-series ferrite is a better choice for that frequency
range, and 70 series is probably better for the relatively high
impedances you're dealing with. And as Richard said, you might have to
do the transformation in more than one step.

Roy Lewallen, W7EL