This article demonstrates the use of the (modified) nanoVNA-H to measure Loss (Transmission Loss) and Insertion Loss of a small ferrite 64:1 RF transformer, and the Insertion VSWR and Return Loss. The transformer was designed for a receive application at 9MHz.
Firstly let’s define the meaning of the terms: Continue reading nanoVNA-H – measure ferrite transformer
This article demonstrates the use of the (modified) nanoVNA-H to capture data from which the complex relative permeability of an unknown ferrite core is calculated and plotted
Above, a single turn of wire through the sleeve allows measurement by the nanovna. The nanoVNA fundamentally captures s11 parameters which we need to convert to relative permeability. Continue reading nanoVNA-H – measure ferrite core permeability
A very common design of a n:1 transformer for EFHW antennas uses a 2t primary on and FT240-43 (or even smaller) ferrite core.
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 nanoVNA-H – measure equivalent core loss resistance
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 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.
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)
Ferrite cored inductors and transformers saturate at relatively low magnetising force.
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
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 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
Commercial products often have power ratings that bear checking.
There are common some key properties that are relevant:
Continue reading Power rating of a ferrite cored transformer or balun
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