Recently, I have had the desire to try my hand at winding toroids. They have always been a mystery to me. Today’s project is winding a toroid for 40-10 meters. My target antenna is one I learned from Thomas, K4SWL. It is a random wire antenna that is 29.5 long with a 17 foot counterpoise. It is a great antenna and works well at park campsites. I either string it up in a tree or I use my 20′ B&M fishing pole https://kk4z.com/2022/05/11/vertical-antenna-support/.
The antenna as pictured above (battery not included), weighs about 3 oz. The antenna while broadbanded can present higher SWR on some frequencies which can reduce transmit power. I decided to try a 9:1 UnUn to see if I can smooth that out. For instructions on how to wind the toroid I used QRP Guys mini unun. I was going to buy their kit, but they were out of stock at the time of this article. Max power is probably about 10 watts.
The form factor I borrowed from OM0ET. His instructions were not that clear but I liked the way it looked. Winding the toroid was probably the most difficult part. I didn’t have 3 different colored magnetic wires, so I had to pay close attention to how they were wound. I little trial and error and this is what I got.
Partially assembled, it looks like this.
Fully assembled it looks like this. I added an optional rope loop to take the strain off of the UnUn.
In use, the antenna is connected to the brass screw. Either a counterpoise or a 20′ or better length of coax connected to your radio can be used. To run a counterpoise which I prefer, you add a BNC Tee connector.
Your coax cable to your radio is connected to the other side of the tee. The counterpoise is made using a crimp style BNC connector. DO NOT use the center pin in the connector or it will short the antenna.
The other end of the counterpoise has an an eye so it can still be used with the old style configuration. I added a little shrink tubing to help with strain relief.
Here is the complete kit.
Weight is under 4 oz. which is less than a 1 oz gain over the old antenna. How does it play? Initial testing with an antenna analyzer showed SWR’s below 3:1. However, this was done quickly with the antenna more horizontal than vertical. It was a hot sunny day and it was time to get inside. This next weekend I have an activation planned and will wring the antenna out, but so far it looks very promising.