I made my first multi band antenna this weekend for 20 and 15 meters for an EFHW wire with a 49:1 unun, to be used with 5 W rig. I used a toroid I had on hand, T80-2.
I hang this antenna in my living room as an inverted L. It's far from an ideal environment.
I have what I think is a 18 pF 1kV ceramic capacitor(marked 18J, NP0). I also have 100 pF 2kV caps.
I first thought I'd use the 100 pF cap since I'm sure of it's value and type. But then the inductance value becomes rather low with trap impedance ~75 Ohms at 21 MHz.
I figured that isn't going to look like an open circuit. I put in the questionable 18 pF cap and wrapped more turns (~20) on the T80-2.
I then added about four more feet of wire to the end and trimmed to get 20 meters in resonance. The lowest SWR I could get is around 2:1.
I probably did not build this correctly to start with. However, my question is: Should I aim for highest impedance possible at the trapped freq? Meaning the lowest capacitance value with highest number of turns on the inductor ?