Building a DIY 9:1 UnUn

Having recently passed my General license exam, I was eager to try to get on HF. This began the hunt for an antenna that didn’t require permanent installation as I live in a rental. Proper dipoles seemed too difficult to string up in temporary installs. I have had some success with portable verticals, but I came across a few accounts of people using their rain gutters as antennas! There’s a well-liked commercial product called the HOA Buster, but given the cost of approx $250 I wanted to see what could be done with a homebrew version. After some research, it seems that while the HOA Buster has some well done matching to get to a ‘it just works’ for most people, some have had good results simply using a 9:1 unun and an atenna tuner to attach their gutters.

After looking up and finding out that even 9:1 ununs range in price form $30 to $50 for the lower wattage versiona and kits, I decided to try my hand at a DIY.

I used a project box approx 2 x 2.5 x 4 inches, along with a SO-239 bulkhead connector and two power pole binding posts. For the ferrite core, I found several on the internet had had good success with a FT140-43 (while others prefer a powderwed iron core for higher outputs). I used an 18 AWG solid core copper wire in 3 colors to make keeping track of the connections easier.

Seems that many have had good luck on the HF frequencies at 8 turns, I chose to do 9 with the following connections:

Color	Beginning Side	Ending Side
red	SO-239 chassis ground and Black binding post	SO-239 center
white	SO-239 center	Beggining end of yellow
yellow	Ending side of white	Red binding post

Testing the finished product with a NanoVNA and a 470 ohm resistor across the binding posts, showed resistance of between 40 and 50 ohms across the HF band. and SWR und 2.5:1 across the sweep.

The UnUn seems to be a success, so now onward to testing the raingutter! I’ll let you know how it works!