A correspondent asked whether I had a tool similar to An improved simple Simsmith model for exploration of a common EFHW transformer designs (v1.03) to assist in the design of a ferrite cored Ruthroff 1:4 balun for HF.
In fact, the problem is the same as the one discussed in the article above, and the model is suited to application to the ferrite cored HF Ruthroff 1:4 balun case.
This analysis applies to a Fair-rite 2843009902 but may not apply to other manufacturer’s BN43-7051.
Above is a screenshot of the model calibrated against measurement. The magenta curve is the prediction and the blue curve is the measurement. Note that very small differences in measured value result in apparently large changes in InsertionVSWR, these two curves reconcile very well, especially considering the tolerances of ferrite material. Continue reading A Simsmith model of a Ruthroff 1:4 voltage balun – 2843009902 (BN43-7051)
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 more discussion).
There are a plethora of designs using FT82-43 published on the ‘net, most of them have appalling loss.
Above is a Simsmith model and measurement of the transformer for reconciliation. The blue VSWR curve is the measurement and the magenta curve is the calibrated model, they agree well considering the tolerance of ferrite materials. 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 be a NiZn ferrite based on its very high resistivity), they sell at $7 for a pack of two.
The first test was of a 2:14 turn winding terminated in a 2450Ω load. The transformer is an autotransformer of 2+12t with 91pF compensation capacitor installed in shunt with the 2t winding.
As expected, |s11| is pretty poor at the low end, corresponding to an InsertionVSWR=1.7 @ 3.5MHz.
Design rejected due to high InsertionLoss, magnetising admittance too high.
3:21 turn windings
The transformer is an autotransformer of 3+18t with 91pF compensation capacitor installed in shunt with the 3t winding. 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 works quite well for low leakage inductance / low ratio transformers but falls down for the higher leakage inductance / higher ratio transformers.
An improved model
The improved model is similar, but Cse in the model above is distributed to the outer sides of the lumped constant model.
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. Continue reading An improved simple Simsmith model for exploration of a common EFHW transformer designs (v1.03)
in the article A simple transformer model of the Guanella 1:4 balun – some further observations I stated:
Note that a two terminal impedance is a naive representation of many if not most antennas, popular, but a naive over simplification that does not facilitate evaluation of current balance.
An example was a recent posting above that used the model to make assertions about the behaviour of a Guanella 1:4 balun.
This article reports results of two experiments with NEC to model an ‘imperfect’ half wave dipole. It is not exactly resonant, but the main issue is that it is tilted from one end to the other, it is not parallel to the ground surface. Continue reading Modelling an antenna as a simple two terminal resistance is often naive
A simple transformer model of the Guanella 1:4 balun discussed a simple model for the operation of the device, but a model that is too simple for most RF baluns. Notwithstanding that, it does expose some interesting issues that are not only valid at lower frequencies, but will also be manifest in an RF balun.
Consider the effect of breaking the connection at the red X, so that we now have what is often referred to as an “isolated load”. Continue reading A simple transformer model of the Guanella 1:4 balun – some further observations
(Guanella 1944) described a 1:4 balun, of a type often known as a current balun.
From Definition: Current Balun, Voltage Balun:
An ideal current balun delivers currents that are equal in magnitude and opposite in phase.
A good current balun will approach the ideal condition. It will deliver approximately equal currents with approximately opposite phase, irrespective of the load impedance (including symmetry).
Common mode current will be small.
If the load impedance is not symmetric, then the voltages at each output terminal will not be equal in magnitude and opposite in phase. (Note that for a truly ‘isolated’ load, one well represented as a two terminal load, the currents MUST be equal in magnitude and opposite in phase, but the voltages may not be equal in magnitude and opposite in phase.)
A simplified model
Above is a schematic of the Guanella 1:4 balun as often presented, this is an edited graphic from the ARRL manual, so may be familiar to readers. Continue reading A simple transformer model of the Guanella 1:4 balun
In the light of Small transmitting loop calculators – a comparison a reader asked my thoughts on yet another small transmitting loop calculator, KB0YH’s STLcalc v2.05.
There are lots of small loop calculators published, and yes, I have added to the number. Most are some form of elaboration of formulas published by (Hart 1986), and given ‘imprimatur’ by ARRL (Straw 2007). These formulas are deeply flawed, see Reconciling W5QJR’s loop formulas.
For that reason, my first step in reviewing any small loop calculator is to look for hints of Hart. Continue reading KB0YH’s STLcalc v2.05
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 a cm grid on the bench. Continue reading Another small efficient matching transformer for an EFHW – 2643251002 – #4 – G8GYW build and measurement