jul 7 2020
Inspired by this excellent article from PeanutPower I decided to build a resonant End Fed Half Wave (EFHW) antenna for portable use. My antenna is designed to be resonant on the digital sections of 15, 20 and 30 meter ham radio bands.
All measurements done with NanoVNA.
You can click on all images below to get a large image.
The 1:64 UNUN is made just like this post that I have published before, with the 100 pF capacitor added later for better 15m SWR. You can see that the SWR is higher on high frequency but it was possible to get a good SWR on 15m, when antenna wire was added.
BNC connector are used because that is my standard for HF and portable connectors.
Sotabeams QRP Pico Traps
Traps used are Sotabeams Pico Traps. It took me a two hours to build, unfortunately I lost the small SMD 100pF capacitor so I used bigger ones. I also need to unwind one turn for each inductor to get in resonant.
Setting up the antenna (wire) sections
This was the most time consuming part. First I used an online antenna calculator to get the sections length. These are the calculated length but I added aprox 50 cm to each before mounting:
|Frq (MHz)||Sections (m)|
|21,1 MHz||6,68 m|
|14,1 MHz||3,4 m|
|10,1 MHz||3,9 m|
Begin with the highest frequency (band). Get the antenna up – measure – down – cut wire – up – measure – down – cut wire…. until you have good SWR for all three bands.
Wire used are from Sotabeams.
This is the result. As you can see very good on 20m and 30m.
On 15m SWR is 1.68:1 – OK but not perfect.
Note: after adding a 100pF capacitor at the input on the UNUN the SWR on 15m got flatter and lower.
This is how the antenna can be used:
And everything ready to go!