It is easy to become focused on the behavior of a component, but don’t lose sight of the fact that it is but a component of a system where components interact, and the system response is the bigger / more complete picture. In the article MismatchLoss of severely mismatched EFHW transformer , a caveat stated … Continue reading MismatchLoss of severely mismatched EFHW transformer – system response
In an social media discussion about loss of EFHW transformers under mismatch conditions, one of the gathered experts said: It doesn’t even have to be highly complex Z. Just presenting an impedance other than 2450 sends the loss through the roof. The back to back transformer test is misleading unless the antenna presents something very … Continue reading MismatchLoss of severely mismatched EFHW transformer
Several readers have asked my thoughts on the ARRL EFHW kit. I have not built and measured the thing, but have done the first step in a feasibility study. The transformer design is not novel, it is widely copied and this may be one of the copies. The design is usually published without any meaningful … Continue reading Thoughts on the ARRL EFHW antenna kit transformer
This article applies the improved model: An improved simple Simsmith model for exploration of a common EFHW transformer designs (v1.03) to the design at Another small efficient matching transformer for an EFHW – 2643251002 – #1 – design workup. Above is the prototype transformer wound with 14t of 0.71mm ECW tapped at 2t. The mm rule … Continue reading Another small efficient matching transformer for an EFHW – 2643251002 – #5 – improved Simsmith model (v1.03)
The transformer is an autotransformer of 3+21 turns single layer close wound on a ‘stack’ of two Fair-rite 5943000601 cores (FT82-43?). Note that these were genuine Fair-rite stock, other #43 mix products in the market place may be significantly different (see Ferrite cored RF chokes in Class-E RF power amplifiers – core material issues for … Continue reading Another small efficient matching transformer for an EFHW – 2 x 5943000601 (FT82-43) – VK4JJ build and measurement
This article documents the process of design, prototyping, measurement and final build of a 1:49 impedance ratio (1:7 turns ratio) EFHW transformer, exploring some alternative designs along the way, a collaboration between VK3PY and VK3TU with a little guidance. The transformer is wound on a Jaycar LO1238 35x21x13mm toroid of L15 material (L15 appears to … Continue reading Another small efficient matching transformer for an EFHW – LO1238 – VK3PY, VK3TU build and measurement
The article A simple Simsmith model for exploration of a common EFHW transformer design – 2t:14t proposed a simple model. The previous proposal Above is the equivalent circuit used to model the transformer. The transformer is replaced with an ideal 1:n transformer, and all secondary side values are referred to the primary side. The model … Continue reading An improved simple Simsmith model for exploration of a common EFHW transformer designs (v1.03)
The article Another small efficient matching transformer for an EFHW – 2643251002 – #2 – prototype bench measurement continued the development of a transformer design. This article analyses measurements at 7.1MHz reported by Mike, G8GYW of his build of a similar transformer. Above is G8GYW’s build, that is an inch grid on the bench. Last … Continue reading Another small efficient matching transformer for an EFHW – 2643251002 – #4 – G8GYW build and measurement
A correspondent asked whether Sontheimer coupler – transformer issues – an alternative design – FT37-43 could be used to inform design of a 49:1 EFHW transformer based on the same core, but with a 2 or 3t primary. In the case of the Sontheimer coupler the winding with the higher number of turns appears in … Continue reading FT37-43 for a 49:1 EFHW transformer enquiry
Another small efficient matching transformer for an EFHW – 2643251002 – #2 – prototype bench measurement continued the development of a transformer design. This article presents a Guanella 1:1 (current) balun (or common mode choke) using the same type of core. Above, the EFHW transformer prototype. Last update: 27th May, 2022, 6:28 PM