20m L/C trap on Fritzel isolator

My 80/40 HWEF has got two traps (one for 20, one for 40) but I never really got the opportunity to take pictures. Now that I’m building a 20m – 10m HWEF, I have made a trap for 15m and took some pictures…

IMG_20200327_223930892Testing for resonance with a single loop on the input of the trustworthy RigExpert AA-54. Because resonance was too low, I took off one turn of the coil.

IMG_20200327_224200965One retangle turn, 11 square turns, 1 retangle turn. Coil measures 2.38 uH, Russian door knob type capacitor measures 22.0 pF. Calculated resonance would be 21.995 MHz but in practice it’s around 21.600 MHz; exactly where I wanted it, a little over the working frequency. I’ve read that when the resonance is in the middle of the working range, losses are very high, when it’s below the working range the wire after the trap will also influence the resonance of the 15m resonance frequency a little, when it’s a little over the working range in frequency, it shouldn’t.

15m trap LC


Close up of the coil, please not that this is the first version that had one turn extra (1 retange, 12 square, 1 retangle), the version on the other pictures has one turn less. The wire is enameled 1.5mm (or so) wire I believe. Going to test it soon with the dedicated 20m-10m HWEF  I made recently.

Keep safe! 73 de PA3HHO