EFHW: progress on 20 meters

I’ve made some progress on the EFHW antenna since my last post here on AmateurRadio.com. I wound a new transformer, but now on a thinner plastic tube. Initially it had a 10:1 ratio, but after some initial tests at home I removed some turns and now it is 8:1.


Today, out on the parking lot, I managed to get a good match on 20 meters with 10 meter wire and a 1 meter counterpoise. A short video to prove this.

It was quiet on 20 meters in mid-afternoon. Only HS0ZJF came in with a reasonably strong signal and it was easy to work him. He gave me a 549 for my 5 Watt QRP signal and I was more than happy with that. And as fate would have it HS0ZJF is originally from Belgium, so we exchanged some Dutch greetings as well.

On 40 meters I wasn’t so successful. This time I tried various lengths of wire, ranging from 19 to 23 meters, but the lowest I could get my SWR was 2.4:1. Funny thing was that the KX3 wouldn’t put out the 3 Watts used when tuning at an SWR of 2.4:1, but it had no problem putting out more at a higher SWR of 3:1 or more. Now the SWR is measured behind 3 meters of coax at the KX3, which is not ideal, so the next step is to make a LED-based resistive SWR bridge to be put right behind the antenna and before the coax.
I could make it tonight, but unfortunately I only had two 51 ohm 5W resistors in my junk box. Back to the shops it is.

Hans "Fong" van den Boogert, BX2ABT, is a regular contributor to AmateurRadio.com and writes from Taiwan. Contact him at [email protected].

4 Responses to “EFHW: progress on 20 meters”

  • Dave, WD8CIV:

    I wonder if a different length counterpoise might help on 40M. The apartment window antenna made by MFJ requires you to adjust the length of the counterpoise by rolling up the free end in order to get the lowest SWR.

  • Hans (BX2ABT):

    Hello Dave,

    Thanks for the reply. I didn’t mention it, but I already tried. The theory says that the counterpoise should be 0.05 lambda, so I tried different lengths between 0.05 and 0.1 lambda. It did make a negative difference using lengths longer than 0.05 lambda, so I am sticking with the original length.

    I also tried using the coax (which is 3 meters in my case) as a counterpoise, but that also made things worse, not better.

  • Glenn W9IQ:

    Hello Hans,

    Don’t forget that with this type of antenna system, you are likely to have common mode currents on the coax. This will fool most SWR meters which may explain the unexpected variances in reported power out.

    – Glenn W9IQ

  • Hans (BX2ABT):

    Hello Glen,

    Good point, had forgotten about that. Hopefully the resistive SWR bridge will give a better indication at the feed point of the antenna.

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