I've build a trap dipole for 20/40m bands. Traps are made of a coil wound on an insulator of RG213 coax and 3 kV NP0 capacitors. The impedance measured with EU1KY antenna analyzer is following:
This is a single trap, before and after putting a heatshrink. The final version of this one is for 14.080 MHz. The second one turned out a bit different, the resonant frequency is 14.150 MHz.
Here is an SWR plot of a final antenna:
The mast is non-conductive, 10 meter high. The balun is 7 turns of RG58 on FT140-43 core. The active impedance is > 1000 Ohm from 80 to 15 meters. The antenna is used in inverted-V configuration.
The antenna was tested using 100W CW. It works OK. However I was surprised to get such a narrow band and SWR >= 1.5 on 20 meters. What brings a question - is it an expected result for trap dipoles? I always thought that it supposed to be more narrowband on lowest band, because traps work as loading coils there. Can it indicate that something is wrong with the antenna?