## Where do µ’ and µ” come from?

Lets say we measure the impedance of a 1t wind on a FT240 size core to have Z=13.6+j19.1Ω @ 7.31MHz.

But it has a resistive component, it is not an ideal or lossless inductor.

Nevertheless, we can consider that Z=j*2*pi*f*L, and since Z is complex, a complex values is implied for L. Continue reading Where do µ’ and µ” come from?

## End Fed Half Wave matching transformer – 80-20m

A prototype broadband transformer for a End Fed Half Wave operated at fundamental and first, second, and third harmonic is presented.

The transformer comprises a 32t of 0.65mm enamelled copper winding on a FT240-43 ferrite core, tapped at 4t to be used as an autotransformer to step down a load impedance of around 3300Ω to around 50Ω. The winding layout is unconventional, most articles describing a similar transformer seem to have their root in a single design.
Continue reading End Fed Half Wave matching transformer – 80-20m

## Line loss under standing waves – recommendation of dodgy tool on eHam

In a discussion about using a 40m centre fed half wave dipole on 80m, the matter of feed line loss came up and online expert KM1H offered:

Use this to help make up your mind. Add it to the normal coax loss. http://www.csgnetwork.com/vswrlosscalc.html

This is to suggest that the feed line loss under standing waves can be calculated with that calculator.

He then berates and demeans a participant for commenting on his recommendation, bluster is par for the course in these venues.

## Calculator analysis

The calculator in question states this calculator is designed to give the efficiency loss of a given antenna, based on the input of VSWR (voltage standing wave ratio) and other subsequent factors.

This is a bit wishy washy, efficiency loss is not very clear. The usual meaning of efficiency is PowerOut/PowerIn, and the usual meaning of loss is PowerIn/PowerOut, both can be expresssed in dB: LossdB=10*log(Loss) and EfficiencydB=10*log(Efficiency). Continue reading Line loss under standing waves – recommendation of dodgy tool on eHam

## Comparing toroidal inductors of different core dimensions

I often see comparisons of toroidal inductors of different core dimensions with all other characteristics (eg turns, core type, frequency) held the same.

There seems an implicit assumption by many that the bigger the core, the larger the inductance. There are several failure in that thinking.

The ‘inductance’ of a toroidal inductor is µ*n^2*a/l where:

• µ is complex permeability, µ0+µr;
• n is the number of turns;
• a is the cross section area; and
• l is the effective magnetic path length.

Note that at RF, permeability may be a complex frequency dependent value, and therefore ‘inductance’ will be a complex value.

Many online calculators incorrectly calculate l from core dimensions using a simplistic formula.

Many online calculators treat permeability as a real number that is not frequency dependent, they use initial permeability (µi). Continue reading Comparing toroidal inductors of different core dimensions

## End fed half wave matching – voltage rating of compensation capacitors

The so-called End Fed Half Wave antenna system has become more popular, particularly in the form of a broadband matching transformer in combination with a wire operated harmonically over perhaps three octaves (eg 7, 14, 21, 28MHz).

The broadband transformer commonly uses a medium µ ferrite toroid core, and a turns ratio of around 8:1. Flux leakage results in less than the ideal n^2 impedance transformation, and a capacitor is often connected in parallel with the 50Ω winding to compensate the transformer response on the higher bands.

David, VK3IL posted EFHW matching unit in which he describes a ferrite cored transformer matching unit that is of a common / popular style.

Above is David’s pic of his implementation. It is a FT140-43 toroid with 3 and 24t windings and note the 150pF capacitor in shunt with the coax connector.

The article End fed matching – analysis of VK3IL’s measurements gives the following graph showing the effects of compensation for various resistive loads. Continue reading End fed half wave matching – voltage rating of compensation capacitors

## Molasses derusting of steel

This article describes a setup for derusting small steel components, mainly machine tool accessories, using a Molasses solution.

A 10% Molasses solution can be an effective way to derust steel. Feed grade Molasses costs about \$2/kg at the local rural store.

The process is bacterial and activity depends on temperature. Experimentation suggests that optimal temperature is 30-35°, and derusting can be achieved in a few days at that temperature (subject to the degree of rust). At lower temperatures, the process may take many weeks. The nice thing compared to electrolytic derusting is that work is unlikely to be damaged by the process.

Above, the rust treatment system comprises:

• Bain marie stainless 1/3 module 200mm deep with lid;
• 1000W electric cooker;
• 230VAC thermostat with thermistor probe immersed in the process liquid;
• 230VAC dimmer to reduce the power of the cooker element.

Above is an internal view of the thermostat made from a Chinese 230VAC thermostat, a 3m extension cord and ABS plastic box. Continue reading Molasses derusting of steel

## Review of inexpensive Chinese thermostat – MH1230A

This is a review of an inexpensive MH1230A Chinese bang-bang  thermostat that was purchased on eBay for around A\$15 complete with thermistor sensor and postage.

Above is the front view of the thermostat. There are many thermostats on the market with similar front panels, but they differ in internals and most importantly, performance and quality.

Above, the rating label is clear and informational, and it does give the sensor parameters.  Continue reading Review of inexpensive Chinese thermostat – MH1230A