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“I can't go back to yesterday because I was a different person then” ~ Alice in Wonderland

I got bored and decided to update my OCF antenna. I was never satisfied with the performance with the OCF design so I thought a Fan Dipole (or in this case a Parallel Dipole) would be a quick project. I could pick and choose the desired bands (40-30-20-10 with 15 as a third harmonic of 40) and a simple 1:1 Choke Balun to interface with my RG-213 feed line. The only Balun I had on hand was a quick and dirty DIY thing I dug out of my junk drawer. What a nice opportunity to make a new one! I had three large ferrite cores salvaged from the interface to a now defunct Cushcraft R7 vertical and started researching with Google to see if they would suffice for this project. Google was not much help so why not try:

Gemini AI !!!

OMG, talking about instant gratification. Gemini not only had the inside info about the cores themselves, but suggested I use all three if I ever wanted to run with 80 meters. Two would be sufficient for 40 and above, but more is better! Then Gemini designed the Balun for me. It suggested winding the stacked cores with RG-316 coax. I had never heard of such a thing. I'm old school and always used magnet wire for balun projects, but keeping the pairs of magnet wire close together and wound neatly without nicking the insulation is always a chore so I decided to go with the coax. Gemini said the tiny coax would be fine for a barefoot 100 watt rig. My first attempt was a jumbled mess. The design calls for 8 passes through the cores, cross over to the other side and 8 more masses through the cores. Then I had the brilliant idea to design and print guides to keep everything tidy. Here's the result:

I'm rather proud of my effort so far. I uploaded the image to Gemini and it gave my design rave reviews!

Now for an enclosure.

The black "boxes" are TPU covers for pairs of Anderson Plugs to connect my 4 dipole pairs. The black band between the two halves of the assembled balun is a TPU gasket with a small amount of waterproof grease to ensure a tight seal. There is an embedded stainless steel turnbuckle to take the stresses of hanging and dipole element support.

The initial wire lengths were intentionally too long for proper resonance. Using my NanoVNA analyzer, I determined the resonance frequency, uploaded the initial lengths, and my desired resonance and Gemini told me how long to fold back the ends of the wires to achieve the desired resonance. Gemini was spot on each and every time. Starting with 40 meters, I made 4 trips outside for the modifications and the results were perfect. What a tremendous time saver!

Update: With the help of Google's Antigravity, I created a dipole length calculator . Calculate the wire length of a dipole using the standard formula and add a bit to each end. Using an antenna analyzer, VNA etc., determine the resonant frequency. Enter that frequency and the desired resonant frequency into the calculator and it will tell you how much wire to fold back or unfold. The calculator works with imperial and metric.

The calculator link is at the top of the page.

“I am not crazy; my reality is just different from yours.” ~ The Cheshire Cat

Home“I can't go back to yesterday because I was a different person then” ~ Alice in Wonderland

Home
“I can't go back to yesterday because I was a different person then” ~ Alice in Wonderland