Designing with binocular ferrite cores – published Al values

Designing with ferrite binocular cores can be frustrating as there are different formats in which data is provided, and data for different mixes on the same dimensioned cores appear inconsistent.

There are several source of the Al parameter for some common cores, often from resellers rather than manufacturers. Continue reading Designing with binocular ferrite cores – published Al values

Designing with binocular ferrite cores – Σ(A/l)

Designing with ferrite binocular cores can be frustrating as there are different formats in which data is provided, and data for different mixes on the same dimensioned cores appear inconsistent.

#61 mix

This article documents calculated geometry Σ(A/l) derived for a number of Fair-rite cores from their specified Al (at µi). Continue reading Designing with binocular ferrite cores – Σ(A/l)

RF transformer design with ferrite cores – saturation calcs

Ferrite cored inductors and transformers saturate at relatively low magnetising force.

#61 material example

Lets work through an example of a FT50-61 core with 10t primary at 3.5MHz.

Magnetic saturation is one limit on power handling capacity of such a transformer, and likely the most significant one for very low loss cores (#61 material losses are very low at 3.5MHz).

Let’s calculate the expected magnetising impedance @ 3.5MHz.

Zm=0.966+j144Ω, |Zm|=144Ω. Continue reading RF transformer design with ferrite cores – saturation calcs

RF transformer design with ferrite cores – initial steps

A review of transformer design

In a process of designing a transformer, we often start with an approximate low frequency equivalent circuit. “Low frequency” is a relative term, it means at frequencies where each winding current phase is uniform, and the effects of distributed capacitance are insignificant.

Above is a commonly used low frequency equivalent of a transformer. Z1 and Z2 represent leakage impedances (ie the effect of magnetic flux leakage) and winding conductor loss. Zm is the magnetising impedance and represents the self inductance of the primary winding and core losses (hysteresis and eddy current losses). Continue reading RF transformer design with ferrite cores – initial steps

An online expert on the unsuitability of #43 for HF UNUNs

An online expert recently advised:

…The spec for type 43 makes it clear that it should never be used for HF unun construction. It is specifically engineered with a complex permeability that makes the core lossy on most HF frequencies. Since an unun is not a TLT (transmission line transformer) but rather an autotransformer, a low loss core is essential for efficient operation….

Now it contains the very common FUD (fear, uncertainty and doubt) that masquerades as science in ham radio, but without being specific enough to prove it categorically wrong. To a certain extent, the discussion goes to the meaning of efficient operation. Continue reading An online expert on the unsuitability of #43 for HF UNUNs

Using SPICE on antenna baluns

Guanella’s 1:1 balun and his explanation gave a LTSPICE model of Guanella’s 1:1 balun.

The LTSPICE model was of a ‘test bench’ implementation of the balun which comprised an air cored solenoid of two wire transmission line, with a slightly asymmetric lumped load.

This article discusses limitations of SPICE in modelling practical baluns.

Guanella’s 1:1 balun and his explanation – Zcm gave the characteristics of a example ferrite cored balun.

Above is Zcm of a 11t balun wound on a FT240-43 toroid. The ferrite core acts on the common mode choke element and has negligible effect on the differential transmission line mode. The key characteristics are: Continue reading Using SPICE on antenna baluns

Guanella’s 1:1 balun and his explanation – Zcm

Guanella’s 1:1 balun and his explanation gave Guanella’s equivalent circuit and analysis of an example air cored choke of the type shown by Guanella.

The analysis was presented in an LTSPICE model of a ‘test bench’ implementation of the balun, and it showed that on a slightly asymmetric load, common balance was only good in a small region around the choke’s self resonant frequency of 41MHz.

One metric that is useful in indicating the effectiveness of a Guanella 1:1 balun in achieving current balance or reducing common mode current is the choking or common mode impedance Zcm of the stand alone balun.

Modern thinking and experience is that |Zcm| needs to be 1000Ω or higher for effective common mode reduction on many HF wire antennas, and considerably higher for some highly asymmetric antennas.

Zcm of the example air cored solenoid balun

Above is Zcm for the example balun. It is very low at low frequencies and rises to 133+j914Ω at 30MHz. Continue reading Guanella’s 1:1 balun and his explanation – Zcm

Guanella’s 1:1 balun and his explanation

It is now 75 years since Guanella’s article “New methods of impedance matching in radio frequency circuits” described the form and operation of what we now commonly call a “Guanella 1:1” balun, but hams being hams also use other terms like “isolator”, “common mode choke”, “current choke” and some insist is it not a balun at all.

In fairness, Guanella did not call the thing a “balun”, but if we accept a very general meaning of balun to be any device intended to facilitate or permit a different state of balance to either side of itself, this is a balun.

Guanella’s description

Above is an extract from (Guanella 1944), and contains an almost complete description of the 1:1 balun. The ideal centre tapped transformers shows are a device for separating the differential and common mode currents so that appropriate elements can be used for those currents. Continue reading Guanella’s 1:1 balun and his explanation

Pawsey Balun – what is it good for?

The Pawsey Balun (or Pawsey Stub) is described as a device for connecting an unbalanced feed to a balanced antenna.

Above is a diagram of a Pawsey Balun used with a half wave dipole (ARRL).

Pawsey Balun on an asymmetric load reported model results in an asymetric dipole antenna, and showed very high common mode feed line current.

Pawsey Balun on an asymmetric load – bench load simulation showed that although the Pawsey balun is not of itself an effective voltage balun or current balun, it can be augmented to be one or the other.

So, you might ask what they do, what they are good for, and why they are used. Continue reading Pawsey Balun – what is it good for?