## Jaycar LO1238 ferrite core

Over many years, the Jaycar LO1238 has appeared in some of my projects. I recommended them for a range of applications, particularly applications optimised for low HF.

Above, the core is 35x21x13mm, a mid sized core, two used in my redesign of a commercial balun and implemented by VK4MQ . The mid size limits dissipation, but compactness can be an advantage. The cores sell for less than \$4.00 per core and are readily available in Australia. Continue reading Jaycar LO1238 ferrite core

## Mornhinweg ferrite core measurements – #31

Further to Amidon’s method of rating ferrite inductors and transformers, this article discusses some interesting measurements of ferrite toroids by Manfred Mornhinweg (Mornhinweg 2019).

Above are his measurements of a FB-31-6873 sleeve. Essentially there are two measurements at each frequency, and the expected flux density B is in the ratio of approximately 2:1. He has fitted a straight line on a log/log graph to the measurements at each frequency. The similarity of the slopes is not unexpected, and is a tribute to his experiment design, execution and calculations. Continue reading Mornhinweg ferrite core measurements – #31

## Gauss based ferrite core loss

A reader of Amidon’s method of rating ferrite inductors and transformers wrote to support Amidon’s approach and cited a video by W0QE.

W0QE’s video #80: High Power Balun with #31 Ferrite Material gives some measurements and simulations of a FT240-31 inductor with 11 and 14 turns.

In the video he states:

It turns out that the heating effects in the coil are related to the voltage across the coil only, not the current through the it or anything else.

In fact, there is current flowing through the inductor and that develops a voltage difference across the ends. When we are talking about the self inductance properties, then we are talking about the voltage induced in the inductor as a direct result of the current flowing through the inductance.

Let’s look at his own figures to demonstrate,

Above is his Simsmith model. Let us focus on just the left hand two elements L and R1 (for the 11t inductor) as it is a quite complicated model. L was derived from a measurement of the inductor in a fixture, and to some extent the fixture is captured. Continue reading Gauss based ferrite core loss

## Disturbing the thing being measured – coax line

An issue that often arises in online discussions inability to reconcile the VSWR indicated by a transceiver (or possibly an inline VSWR meter) and an antenna analyser.

Is this Segal’s law at play?

There are several common contributors including:

• faulty, dirty, or not properly mated connectors and cables;
• VSWR meters that are not accurate at low power levels; and
• influence of the common mode current path on VSWR.

## Amidon’s method of rating ferrite inductors and transformers

I have set out an initial design method for RF inductors and transformers using toroidal ferrite cores and over time I get correspondence drawing my attention to Amidon’s advice, specifically sections 1-35 and 1-36.

Section 1-36 states explicitly that it is applicable to Iron Powder and Ferrite, which is interesting because they are very different materials from a loss point of view.

Basically, their method depends on a maximum safe value for peak flux density.

They give an expression for peak flux density $$B_{max}=\frac{10^8E }{4.44 A_e N F}$$ and the following table of design limits for Bmax.

Note that the table and formula are independent of ferrite mix type (though they do mention that “these figures may vary slightly according to the type of material being used.” Continue reading Amidon’s method of rating ferrite inductors and transformers

I see online discussions struggling to try to work out if a receiving system is sufficiently good for a certain application.

Let’s work an example using Simsmith to do some of the calculations.

Scenario:

• 20m ground mounted vertical base fed against a 2.4m driven earth electrode @ 0.5MHz;
• 10m RG58A/U coax; and
• Receiver with 500+j0Ω ohms input impedance and Noise Figure 20dB.

An NEC-4.2 model of the antenna gives a feed point impedance of 146-j4714Ω and radiation efficiency of 0.043%, so radiation resistance $$Rr=146 \cdot 0.00043=0.0063$$.

Above, the NEC antenna model summary. Continue reading Quantifying performance of a simple broadcast receive system on MF

## nanoVNA – measure Transmission Loss – example 4

This article is demonstration of measurement of Transmission Loss in a section of coaxial transmission line. The scenario is chosen to expose the experiment to some of the things that complicate such measurements.

The very popular nanoVNA-H will be used to make the measurements.

The scenario:

• nanoVNA fully calibrated from 1.5-1.8MHz using a 200mm length coax lead on Port 2 (nanoVNA CH1);
• 10m of RG58C/U; and
• f=1.65MHz.

Above is a block diagram of the test configuration. nanoVNA measurements are wrt 50Ω, so $$P=\frac{V^2}{50}$$ and $$V=\sqrt{50P}$$. Continue reading nanoVNA – measure Transmission Loss – example 4

## KL7AJ on the Conjugate Match Theorem – analytical solution – Simsmith

KL7AJ on the Conjugate Match Theorem asked the question Should we have expected this outcome?

Let us solve a very similar problem analytically where measurement errors do not contribute to the outcome.

Taking the load impedance to be the same 10.1+j0.2Ω, and calculating for a T match similar to the MFJ-949E (assuming L=26µH, QL=200, and ideal capacitors) with Simsmith we can find a near perfect match.

The capacitors are 177.2 and 92.9pF for the match. Continue reading KL7AJ on the Conjugate Match Theorem – analytical solution – Simsmith

## nanoVNA – measure Transmission Loss – example 3

This article is demonstration of measurement of Transmission Loss in a section of coaxial transmission line. The scenario is chosen to expose the experiment to some of the things that complicate such measurements.

The very popular nanoVNA-H will be used to make the measurements.

The scenario:

• nanoVNA fully calibrated from 1-5MHz using a 200mm length coax lead on Port 2 (nanoVNA CH1);
• 35m of CCS RG6/U (close to an electrical quarter wavelength);
• 75-50Ω Minimum Loss Pad (5.72dB); and
• f=1.65MHz (close to a quarter wavelength.

Above is a block diagram of the test configuration. nanoVNA measurements are wrt 50Ω, so $$P=\frac{V^2}{50}$$ and $$V=\sqrt{50P}$$. Continue reading nanoVNA – measure Transmission Loss – example 3

## nanoVNA – measure Transmission Loss – example 2

This article is demonstration of measurement of Transmission Loss in a section of coaxial transmission line. The scenario is chosen to expose the experiment to some of the things that complicate such measurements.

The very popular nanoVNA-H will be used to make the measurements.

The scenario:

• nanoVNA fully calibrated from 1-5MHz using a 200mm length coax lead on Port 2 (nanoVNA CH1);
• 35m of CCS RG6/U (close to an electrical quarter wavelength);
• three 50Ω terminations in shunt with VNA Port 2; and
• f=1.65MHz (close to a quarter wavelength.

The transmission line load is four 50Ω loads in parallel, one of them being VNA Port 2. Only one quarter of the output power is captured by the VNA, so there is effectively a loss of 6.02dB in that configuration. It also delivers a 12.5+j0Ω load the the transmission lines, VSWR is about 6. Note this power division is based on the assumption that Zin of Port 2 is 50+j0Ω, and error in Zin flows into the result. A 10dB attenuator is fitted to Port 2 prior to calibration to improve accuracy of Zin.

Above is a block diagram of the test configuration. nanoVNA measurements are wrt 50Ω, so $$P=\frac{V^2}{50}$$ and $$V=\sqrt{50P}$$. Continue reading nanoVNA – measure Transmission Loss – example 2