Fair-rite’s ‘new’ #43 permeability data

Fair-rite publishes spreadsheets of the complex permeability characteristic of many of the ferrite mixes. This note is about #43 mix and clarification I sought from Fair-rite.

Question

I note that recently, the published table of #43 permeability changed subtly but significantly. Does this table apply to historical product, or does it only apply to new product, ie was there an actual change in the mix, or what it the result of better measurement of characteristics?

Continue reading Fair-rite’s ‘new’ #43 permeability data

Surely there cannot be more forward power than the transmitter makes?

Let’s explore a simple numerical example of a practical line operating in Transverse Electro Magnetic (TEM) mode (the usual thing for practical coax lines at HF).

Let’s review the meaning of 50Ω line.

It means that the line geometry imposes a natural constraint on a wave travelling in the line that V/I=50… but remember that TEM waves are free to travel in (only) two directions. This natural ratio of V/I is called the characteristic impedance Zo. Continue reading Surely there cannot be more forward power than the transmitter makes?

Select a ferrite core material and sufficient primary turns for a low InsertionVSWR 50Ω broadband RF transformer – nanoVNA – loss components graph

Select a ferrite core material and sufficient primary turns for a low InsertionVSWR 50Ω broadband RF transformer – nanoVNA gave an explanation of how to use a nanoVNA or the like to select a suitable core and sufficient turns for a low InsertionVSWR broad band 50Ω transformer. Continue reading Select a ferrite core material and sufficient primary turns for a low InsertionVSWR 50Ω broadband RF transformer – nanoVNA – loss components graph

A DIY thermostat based on the MS1230A controller

This article documents the build of a DIY thermostat based on an inexpensive ($12) Chinese temperature controller.

Controller module

The controller used is a 220VAC MH1230A.

Above is an internal view of the controller. Importantly it has a relay rated at 240V 30A, and 15A at PF=0.4. The datasheet rates the relay for a 2HP (1.5kW) motor. It uses a ‘conventional’ power supply, the brown component is the power transformer. Most similar products use inadequate relays and have low grade switched mode power supplies that create RF noise. Continue reading A DIY thermostat based on the MS1230A controller

Select a ferrite core material and sufficient primary turns for a low InsertionVSWR 50Ω broadband RF transformer – nanoVNA

This article demonstrates the use of a nanoVNA to select a ferrite core material and sufficient primary turns for a low InsertionVSWR 50Ω broadband RF transformer.

Simple low frequency equivalent circuit

Above is a very simple approximation of an ideal 1:1 transformer where the effects of flux leakage and conductor loss are ignored. A 1:n transformer can be modelled the same way, as if flux leakage and conductor loss are ignored, the now ideally transformed secondary load becomes 50Ω. Continue reading Select a ferrite core material and sufficient primary turns for a low InsertionVSWR 50Ω broadband RF transformer – nanoVNA

Phase of s11 and Z

Antenna system resonance and the nanoVNA contained the following:

Relationship between angle of reflection coefficient and angle of impedance

It was stated above that the angle (or phase) of s11 or Γ is not the same as the angle (or phase) of Z.

Given Zo and Γ, we can find θ, the angle of Z.

\(
Z=Z_0\frac{1+\Gamma}{1-\Gamma}\)

Zo and Γ are complex values, so we will separate them into the modulus and angle.

\(
\left | Z \right | \angle \theta =\left | Z_0 \right | \angle \psi \frac{1+\left| \Gamma \right | \angle \phi}{1-\left| \Gamma \right | \angle \phi} \\
\theta =arg \left ( \left | Z_0 \right | \angle \psi \frac{1+\left| \Gamma \right | \angle \phi}{1-\left| \Gamma \right | \angle \phi} \right )\)

We can see that the θ, the angle of Z, is not simply equal to φ, the angle of Γ, but is a function of four variables: \(\left | Z_0 \right |, \psi , \left| \Gamma \right |, \& \: \phi\) .

It is true that if ψ=0 and φ=0 that θ=0, but that does not imply a wider simple equality. This particular combination is sometimes convenient, particularly when ψ=0 as if often the case with a VNA.

This article offers a simulation of a load similar to a 7MHz half wave dipole.

The load comprises L, L1, and C1 and the phase of s11 (or Γ) and phase of Z (seen at the source G) are plotted, along with VSWR. Continue reading Phase of s11 and Z

The quarter sized G5RV with hybrid feed

(Varney 1958) described his G5RV antenna in two forms, one with tuned feeders and the more popular form with hybrid feed consisting of a matching section of open wire line and then an arbitrary length of lower Zo coax or twin to the transmitter.

(Duffy 2005) showed that the hybrid feed is susceptible to high losses in the low Zo line as it is often longish, is relatively high loss line and operates with standing waves.

Lets look at measurement of a real antenna, broadly typical of the G5RV. The antenna measured is a G5RV rigged in Inverted V form, 11m height at the apex and around 8m at the ends. The feed line is 2mm diameter copper spaced 50mm with occasional plastic insulators.

To some extent, the measurements are dependent on the environment, and whilst there will be variation from one implementation to another, the measurements provide a basis for exposing the configuration challenge.

Screenshot - 01_05_16 , 19_33_56

Above is a plot of VSWR(50) essentially at the lower end of the matching section and low Zo line. The measurement is made looking into 0.5m of RG142 and a Guanella current balun that uses about 1m of 110Ω pair, it is essentially the load end VSWR of a hybrid feed were it used. Continue reading The quarter sized G5RV with hybrid feed

A thermostatically controlled pot for waxing leg hold traps

We periodically have problems with rabbits from an adjoining reserve, and this summer has been bad enough to do something about the crepuscular critters.

Leghold traps from the factory are usually covered in some type of rust resisting oil combined with the residues of the manufacturing processes, all of which needs to be removed to de-scent the traps.

Practice varies, I spray them with ordinary degreaser and then after 5 min jet them clean with water.

There are a range of practices to colour and wax the traps, for rabbits I simply wax them and with supply shortages, I experimented with ordinary soy wax for container candles. This wax does not try hard, so it is not inclined to crack off, and it reduces rusting whilst lubricating moving parts.

Above is a pair of Victor Softcatch #1 traps that have been cleaned, lightly rusted (for colour), cleaned again and waxed. I also use Bridger #1.65 traps which do not rust as easily, so they are used without colouring at all and they seem every bit as successful when covered in sieved soil.

OTS

Above, the 7.6l stainless stock pot from Big W (~$11), a 1100W coil type electric cooker (~$20). Continue reading A thermostatically controlled pot for waxing leg hold traps

The devil is in the detail…

An image from one of my articles has been posted online in some discussions, with attribution of the underlying image, but it includes some changes / annotations.

I think that this is a better image.

The difference is in the two pin assembly at lower centre, an addition to my original image. My recommendation is that the DUT is attached to the same side of the pin strip as was used for the calibration parts, as shown. Though I did not intend that this jig be used much above 100MHz, small details like this might improve its accuracy. Continue reading The devil is in the detail…