Cut the wire in between the transformer and the 40m L/C trap with 30cm and the dip was spot on. Resonance on 80m was still a little low (around 3.6 MHz) so I cut the tail wire after the trap with 20cm and folded back 10cm. Here are the results!
Now that’s a pretty picture… Let’s zoom in:
Because the half wave for 80m effectively is loaded with a 20 uH coil the bandwidth is a little small but still under 1:3 on the whole band and 1:1.45 at best. I found that the R of the antenne on both 80m and 40m is a little over 50 Ohms so I will probably add a turn or two to the transformer. Not sure which one I’m going to use though. I might first want to try the multicore transformer configured from 2 x FT140-52 and 4 x FT82-52 inside but I might as well be using the single FT240-52 transformer with 4:28 or even 5:35 ratio. Here’s what 40m looks like:\
Nice! Better the 1:1.7 on the whole band. Also here the R is a little too high so a little more transformation is required. Will do that later, first test this to see how it works.
I’ll keep you posted!
73 Pleun (PA3HHO)