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I purchased a H4 back about 12 ago.
Up until now, it's only been used for SWR testing, but now I want to test the Chokes & Unun's I build.
I have watched a number of YouTube videos on how this done using S21.

I have noticed that most place a 10 dB Attenuator on the S21.

Is this really needed, or can I test without it?

Pete DU7/VK4CCV

This is how I checked my 49:1 unun for EFHW with NanoVNA:


73
Jon, VU2JO

On Wed, May 7, 2025 at 12:47?PM VK4CCV via groups.io <Fritzables=
[email protected]> wrote:

I purchased a H4 back about 12 ago.
Up until now, it's only been used for SWR testing, but now I want to test
the Chokes & Unun's I build.
I have watched a number of YouTube videos on how this done using S21.

I have noticed that most place a 10 dB Attenuator on the S21.

Is this really needed, or can I test without it?

Pete DU7/VK4CCV

I tested my unun by placing a 2400 ohm resistor in series with the S21 input. This loads the secondary with approximately 2450 ohms which is the typical source resistance for an EFHW


--
Mike G8GYW

Jon & Mike,

Thanks very much with this.
I have learnt so much over the past 24 Hours and still a long way to.

Cheers


Pete

On Wed, May 7, 2025 at 11:19 PM, Mike wrote:

I tested my unun by placing a 2400 ohm resistor in series with the S21 input.
This loads the secondary with approximately 2450 ohms which is the typical
source resistance for an EFHW

Mike, you can use this program to measure your transformer without using a resistor. It lets you vary the effective resistance by typing instead of soldering.



Brian

I have also learned a good bit from this discussion Pete.

73
Jon, VU2JO

On Thu, May 8, 2025 at 3:41?PM VK4CCV via groups.io <Fritzables=
[email protected]> wrote:

Jon & Mike,

Thanks very much with this.
I have learnt so much over the past 24 Hours and still a long way to.

Cheers


Pete

Hey Jon,

Yes mate, despite the age, if aren't learning something new every day, then there's something wrong .
Always great to step outside of the circle once in a while Jon.

Have an awesome day.


Pete

The impedance of an EFHW is dependent on many factors such as surroundings, groung and wire gauge and changes at the higher harmonic frequencies. Has anyone actually measured the antenna?

Mike N2MS

I don't plan on putting one up. I do not see it as the best antenna to use.
People say they have worked a lot of stations with it, but others have said
they worked people using a gutter or bedspring as an antenna. :-)

The best 40m antenna I have built and used was a vertical magnetic loop
antenna, 58 feet long for the horizontal run, 12 feet high vertically. I
had the bottom wire 5 feet off the ground. It was a two-turn loop with a
quarter wavelength of 70 ohm cable at the feedpoint, which made the
impedance at the other end of the 70 ohm cable 50 ohms. Low radiation angle
made it an outstanding DX antenna on 40m. I ran the design on MININEC and
it predicted a gain of 5.5 dB over a dipole off the sides. Of all the 40m
antennas I've used, it was second only to a 40 meter beam.

Zack W9SZ

On Thu, May 8, 2025 at 1:38?PM Mike N2MS via groups.io <mstangelo=
[email protected]> wrote:

The impedance of an EFHW is dependent on many factors such as
surroundings, groung and wire gauge and changes at the higher harmonic
frequencies. Has anyone actually measured the antenna?

Mike N2MS

On 05/08/2025 2:19 AM EDT Mike via groups.io < mail@...

wrote:


I tested my unun by placing a 2400 ohm resistor in series with the S21
input. This loads the secondary with approximately 2450 ohms which is the
typical source resistance for an EFHW


--
Mike G8GYW

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