jul 26 2019
After some “not so good attempts” making a EFHW trafo I made a new one with a real FT240-43 Amidon Toroid. I followed this guide:
Construction transformer: https://vk3il.net/projects-antenna/efhw-matching-unit/
This is the transformer in a waterproof box:
The measurements with a 5 kohm resistor (yes I know it’s a little to high impedance) gave the following result with my antenna analyzer:
And after adding a Sotabeams wire (https://www.sotabeams.co.uk/antenna-wire-lightweight-100m/ ) and cutting it to resonate on 7 MHz (40 meter) I got the measurement below. The wire was very low over ground, just 2 meter. I did not measure the exact length of the wire.
It is very good on 40 m but I can not get the SWR under 3.0:1 at 20 m and 15 m. This is no problem as I will run this antenna with a remote tuner from LDG. It seems that I can use this antenna on 80 m also…
What I understand is that some commercial antennas use some kind of loading coil to make it resonate on higher bands.
Below is the measurement with the wire mounted from the roof to a tree in the garden. As you can see it is much better at higher level above ground and even possible to use at 80m! It can be used without tuner on 40m (SWR 1.5:1). Resonance for 20m and 15m is to high
When using a LDG remote tuner RT-100 it is no problem using all HF bands. Below are some pictures after mounting. I will probably make a better setup later at some other place on the roof of the house.