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Title: Variable loading coil for 8' whips Post by: ka1tdq on May 01, 2020, 12:38:29 AM This was a 100% junk box project. The only thing I needed to buy was some Tarn-X to clean the coil.
The old ARRL handbooks had coil loading data for 8' whips. I made one for 20 meters and it worked great! Then I thought I'd make something so that I could use on any band. This loading coil has enough inductance for almost anything being 110uH. The center conductor of the coax taps near the bottom of the coil for impedance matching, and the top tap is for how much total inductance you need for the band. One wire off the end connects to vehicle ground and the other goes to the 8' whip. This is obviously for stationary operation. The Arizona heat is brutal on electronics so I don't keep my HF radio in the car. I made this radio mount so that I can throw it in the passenger seat when I want to play. Jon Title: Re: Variable loading coil for 8' whips Post by: ka1tdq on May 18, 2020, 04:22:00 PM That didn't work out so well, so version 2. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
This is an L-tuner that can tune high or low impedance antennas by using the toggle switch to move the capacitor(s) to either the transmitter or antenna side of the coil. I had to solder stubs onto the coil to tap it easier. I used alternating turns in an up/down pattern to maximize the room for the alligator clip. The variable cap goes to almost 500pf, and I can switch in an additional 470pf or 1000pf if needed. Jon |