QRP L- tuner for 5 MHz … 28 MHz

Recently I came across an article from Andrew, VK1AD, in which he describes a QRP L- tuner for 3.5 MHz to 52 MHz. It can be found here.
Andrew’s article is based on an essay by Peter, VK3YE, published in VK’s Amateur Radio magazine, Edition 5, May 2017.
I really wanted to try this easy to build L- tuner, because I thought it might perform even better than my EFHW- transformers (UnUns) and the EFHW- dipole I’m currently using for my SOTA activations.


EFHW Transformer

1. First steps with FT140-43

The impedance of an End Fed Half Wave (EFHW) dipole lies in a range of approx. 2k Ohm to 4k Ohm. In order to achieve a reasonable matching at 50 Ohm, a transformer can be used.
As a starting point I simply copied the design of a broadband transfomer, using a ferrite toroid FT 140-43 from Amidon with a turns ratio of 3:24. The transmission ratio, which is the square of the turns ratio (1:8), is 1:64. This means an impedance of 3200 Ohms will be transformed to 50 Ohms. The above mentioned range of 2k to 4k will fall in a range of approx. 30 to 60 Ohms which results in a slight (but acceptable) mismatch.
There are several manuals available, e.g. here or here.

Edit 2021-11-03: There is a discussion on the SOTA-Reflector which indicates, that the cross-over winding technique causes additional loss. Apparently it is more efficient to make all windings as close as possible.


EFHW- Dipole with Traps

While searching for an alternative to my Linked- Dipole I tripped over the posting of Pedro, CT1DBS, illustrating an end-fed half-wave (EFHW)- Dipole with Traps. Here is the Link to his article. With this design changing bands can be done in no time thaks to the traps. Lowering or modifying the antenna is no longer necessary.
Another very good manual, written by Heinz, HB9BCB, can be found here.