At this writing, I have 12 radials at the base, with various lengths of 15 to 40 feet over very rocky soil (granite, gneiss).
I did no modeling - just threw up some wire that fit my physical situation. Impedance at resonance was around 24 Ohms.
I wound a test transformer on an old toroid of unknown characteristics just to see if I could get close to a 50 Ohms match. That was successful and I even made several contacts at QRP levels.
I decided to wind a better (and I hope, more efficient) version. I used a FT-150A-K core from Amidon along with 10 feet of AWG#14 HAPT wire and some glass cloth tape. The transformer I chose was the W2FMI-2.25:1-HU50 from the Amidon Transmission Line Transformers Handbook on the Amidon website. this is a Jerry Sevick design. I am, of course, using it 'backwards'...
To the right is the toroid as wound. Sevick notes that the #14 takes some effort to wind and suggests leaving long leads on each end for leverage. Good advice.The image below shows (unclearly - sorry) the connections before soldering.
And here is the wired version with the "proof of concept " un-un to the left. The box is an outdoor junction box (with water-sealed lid, not shown) that I picked up at a local big-box store. Pretty handy.
And here it is as installed. The BNC feed to the shack is at the bottom, the inverted "L" connects to the right and the ground and radials to the left.
So far, I am very pleased to get something cheap and easy working for 160M. This might not be the best antenna, but for my circumstance it is up and working. At 1810KHz, the antenna presents a SWR of about 1:1.1, rising quickly away from that QRP frequency.
I do appreciate Mr. Sevick's work.
Now for more radials!
cln - Nick
WB5BKL
Lake Buchanan
