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Amateur Radio

EFHW-4010 DIY antenna

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:

EFHW transformer

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:

5 kohm test measurement

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.

Measurement with wire

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

Measurement after mounting

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.

LDG remote tuner and box with 1:64 UNUN
Other picture of LDG remote tuner and box with 1:64 UNUN
The wire is up in the air…

Updated 2019-12-31

New mounting at roof for trafo and tuner:

2 svar på ”EFHW-4010 DIY antenna”

Your transformer is a 2:16 winding ratio, and a 1:64 transformer, not an unun…perhaps take the 14. winding to the antenna, and achieve a 1:49 transformation to improve swr…..then add a 100pf 15KV capacitor across the feed….yours seems a little lower voltage, and may not last?
Best 73 Henrik

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