Category: EFHW

Ellington describes in a Youtube video his high power matching transformer for an EFHW, he rates it suited to 500W CW.

Like almost all such ‘designs’, they are published without supporting measurements or simulations.

The transformer is intended to be used with a load such that the input impedance Zin is approximately 50+j0Ω, Gin=0.02S.

Analysis of a simple model of the transformer with a load such that input impedance is 50+j0Ω gives insight into likely core losses.
Continue reading Ellington 3 x FT240-52 matching transformer for an EFHW

I have written some recent articles about or relevant to PD7MAA’s BN43-202 EFHW matching transformer. At about the same time a discussion started on and through that discussion, one ‘online extra expert’ stated that my analysis was bogus (dictionary meaning: not genuine, faked, a misrepresentation).

This article presents detail that was not included in the earlier articles as it distracts from the issue for most readers. Continue reading PD7MAA’s BN43-202 matching transformer for an EFHW – full measurement set

I have written many reviews of published EFHW matching transformers, and in most cases the reviews have reported estimated or measured losses that are appalling and not disclosed by the ‘designers’.

Why is it so?

I am asked, why is it so?

Up front, I do not know the answer definitively, but let me offer some thoughts based on the designer’s own articles and discussions by ‘online experts’.

Apparent reasons include:

1. lack of understanding of ferrite and powdered iron core material behaviour;
2. lack of understanding of coupled coils, and mutual inductance;
3. use of inductor design tools that are inadequate at radio frequencies;
4. lack of competency in basic linear circuit theory analysis for AC circuits;
5. failure to make meaningful measurements of the built article;
6. focus on input VSWR as a single metric indicating goodness;
7. reliance on QSOs for evidence of performance;
8. an attitude that antenna system radiation efficiency doesn’t matter, particularly for QRP (if the term antenna system radiation efficiency is even understood as a quantitative metric).

Continue reading Common failings of EFHW matching transformers

At PD7MAA’s BN43-202 matching transformer for an EFHW I gave an estimate of the core loss in PD7MAA’s transformer.

This article reports measurement of a prototype built to his design.

Above is PD7MAA’s graphic for his transformer. It is a little confusing as an 11t wind will start and finish with ends as the blue wind, so the red winding must have and odd number of half turns which suggests the windings are actually 1t and 5.5t (pity he did not show a picture of the real transformer).

PD7MAA gives some measurements for his transformer with a 3300Ω load, but he does not give loss measurements. This experiment is to replicate his configuration, measure the loss and compare it to the estimate given at PD7MAA’s BN43-202 matching transformer for an EFHW.

The prototype uses 1t primary and 5.5t secondary. The secondary load is a 3300Ω resistor in series with the VNA 50Ω input port.

Above is a screen shot of a sweep from 6 to 8MHz. The key data is that shown for the marker at 7.1MHz. Continue reading PD7MAA’s BN43-202 matching transformer for an EFHW – measurement of a prototype

End Fed Half Waves have certainly captured the minds of QRP aficionados, and there is a steady stream of ‘designs’ appearing on the ‘net.

A recent article by PD7MAA describes such a transformer using a BN43-202 balun core for up to 20W PEP from 7-29MHz.

Above is PD7MAA’s graphic for his transformer. It is a little confusing as an 11t wind will start and finish with ends as the blue wind, so the red winding must have and odd number of half turns which suggests the windings are actually 1t and 5.5t (pity he did not show a picture of the real transformer). Let’s proceed under that assumption. Continue reading PD7MAA’s BN43-202 matching transformer for an EFHW