9:1 Impedance Transformer

I have constructed a 9:1 unbalanced to unbalanced (unun) impedance transformer based on a published design by Peter VK6YSF.  Over the next six months or so my plan is to experiment with end fed antennas for 80 and 160m, suitable for a QRP SOTA deployment from the summit of Mount McDonald VK1/AC-048.

My current 80m SOTA antenna is a home-brew half wave inverted V dipole, which will be useful as a baseline to compare an end fed arrangement on a hilltop. BTW there is nothing wrong with my 80m half wave dipole, I just like to experiment with different antenna options, after all our hobby amateur radio encourages experimentation and home-brew construction methods.  Brand name wire antennas and baluns can be constructed at home.

Work in progress..


Jaycar L15 ferrite toroid
Jaycar waterproof plastic case
1 mm enamelled copper wire 18 gauge
2 3/16 inch brass screws
4 3/16 inch brass nuts and washers
2 3/16 inch solder tabs
1 SO239 flange socket
4 3 mm screws, nuts and washers

Testing of the input impedance between 1.8 MHz and 30 MHz, as seen by a radio at 50 ohms, produces a good VSWR match with the antenna terminals terminated in a 450 ohm resistive load.  I will update this post with data obtained from my antenna analyser.

9:1 unun. I plan to secure the toroid in place

3/16 inch brass crews, washers and nuts

Chassis mount SO-239 socket

More to come..