## Power in a mismatched transmission line

This is a republication of an article posted on VK1OD.net Jun 2012.

This article presents a derivation of the power at a point in a transmission line in terms of ρ (the magnitude of the complex reflection coefficient Γ) and Forward Power and Reflected Power as might be indicated by a Directional Wattmeter. Mismatch Loss is also explained. Continue reading Power in a mismatched transmission line

## 80m half wave dipole made from 0.91mm steel MIG wire

Hams being innovative come up with a myriad of cheap alternatives for wire for antennas. One of those alternatives is common 0.91mm steel MIG wire.

Steel MIG wire is often coated with copper and is claimed by some online experts to “work real good”, particularly as a stealth antenna.

But is it the makings of a reasonably efficient antenna?

This article applies the model developed at A model of current distribution in copper clad steel conductors at RF to estimate the effective RF resistance of the wire at 3.5MHz.

## Copper coated round steel conductor (MIG wire) – 0.91mm single core

In fact copper is an undesirable and restricted contaminant of steel welding wire, high grade MIG wire is not copper coated.

Copper content is held to less than 0.05% in the core, and less than 0.05% in the coating… which on my calcs says the coating of common 0.91mm MIG wire is less than 0.125µm…. basically it is a small diameter wire with low conductivity and high permeability. Continue reading 80m half wave dipole made from 0.91mm steel MIG wire

## 80m half wave dipole made from galvanised fence wire

Hams being innovative come up with a myriad of cheap alternatives for wire for antennas. One of those alternatives is galvanised steel fence wire.

A small roll of galvanised tie wire can be purchased from Bunnings hardware for about $10 for 95m… so at$0.10/m it looks like an economical solution.

But is it the makings of a reasonably efficient antenna?

This article applies the model developed at A model of current distribution in copper clad steel conductors at RF to estimate the effective RF resistance of the wire at 3.5MHz.

## Galvanised round steel conductor – 1.5mm single core

A sample of new unweathered wire was measured to determine the approximate zinc coating depth, it was 15µm. Note that zinc is a sacrificial coating and it will erode through life, so this study is an optimistic one of wire when new. Continue reading 80m half wave dipole made from galvanised fence wire

## Skin depth in copper at 1.8MHz according to QRZ

Having just written again on skin effect and copper clad steel (CCS) conductors on HF, and the potential for less than copper performance, it was interesting to note a thread on QRZ where the OP asked for advice on the issue with budget CCS RG-11.

Two late posts as I write this were:

There really is no real issue with skin effect on HF bands with copper clad materials.

and…

At 1.8 MHz, the skin depth in copper is 0.654 micro-meters (.0000654 mm), so the copper cladding on the center conductor of most RG-11 type coaxial cables is more than sufficient for any of our current bands.

The specific advice above looks interesting, convincing even… but thankfully, the skin depth in copper is nowhere near either of the figures he gave. Continue reading Skin depth in copper at 1.8MHz according to QRZ

## Reconciliation of Duffy CCS model with N7WS ladder line measurements

In developing and implementing A model of current distribution in copper clad steel conductors at RF reconciliation against some other published data was important.

(Stewart 1999) published a set of measurements of the popular Wireman windowed ladder line products. His measurements were in the range 50-150MHz. They form the basis for most calculators on quantitative analyses at HF, despite the fact that it is a dangerous extrapolation for CCS construction.

Nevertheless, the directly stated measurements at 50MHz are a useful calibration point for reconciliation.

Above is Table 1 from Stewart, it sets out measurements of four Wireman m.products and a plain copper line.

The table below compares Stewart’s measurements with the CCS model and with TLDetails results (where available). Continue reading Reconciliation of Duffy CCS model with N7WS ladder line measurements

## A model of current distribution in copper clad steel conductors at RF

A model for current distribution in a conductor is that for a homogenous conducting half space with surface current parallel to the interface. Current density at depth d is given by the expression $$J=J_0 \cdot e^{(-(1+\jmath ) \cdot \frac dδ)}$$ where δ is the skin depth $$δ=(ω \cdot µ \cdot σ)^{0.5}$$, σ is the conductivity). This is a model for a plane wave in an infinite block of conductor, so there are some issues caused by curvature of the wire surface, more so towards the centre.

## Copper round conductor – 1.024mm (#18) single core

Fig 1 is a plot of the current distribution in a 1mm dia (#18) round copper conductor at 1.8MHz as implied by the model. Note that while the magnitude of current decays exponentially with depth, there is an imaginary component that hints a curl of the E and H fields within the conductor. Continue reading A model of current distribution in copper clad steel conductors at RF

## Loss of ladder line: copper vs CCS (DXE-LL300-1C)

DXE sell a nominal 300Ω ladder line, DX Engineering 300-ohm Ladder Line DXE-LL300-1C, and to their credit they give measured matched line loss (MLL) figures.

Let’s start by assuming that the offered data is credible, let’s take it at face value.

They make the common ham mistake of writing loss figures as -ve dB where in fact by definition they are +ve (MLL=10*log(Pin/Pout)).

The line is described as 19 strand #18 (1mm) CCS and the line has velocity factor (vf) 0.88 and Zo of 272Ω.

Let us calculate using TWLLC the loss at 2MHz of a similar line but using pure solid copper conductor with same conductor diameter, vf and Zo. We will assume dielectric loss is negligible at 2MHz Continue reading Loss of ladder line: copper vs CCS (DXE-LL300-1C)

## Loss in open wire + coax hybrid feed arrangements

I saw a question posed online about the merits of a proposed antenna system which used a hybrid feed arrangment as 15′ (sic) of the feed line needed to be buried.

Above is the poster’s diagram, and his posting lacked some important details so let’s make some assumptions. Lets assume the antenna is at 150′ in height above average ground, and since the dipole is long enough to be usable on 160m, let’s study it at 1.85MHz.

Input impedance of the dipole under that scenario is around 45-j400Ω.

Let’s consider two options:

• a tuned feeder option (ie open wire line all the way to the ATU); and
• the hybrid feed arrangement shown.

Let’s get serious and use home made open wire line made from 2mm diameter copper spaced 150mm. The very popular 19strand windowed ladder lines using CCS do not have sufficient copper to give copper like performance, the single core CCS is marginal. Continue reading Loss in open wire + coax hybrid feed arrangements

## An Insertion VSWR test gone wrong

We often learn more from failures than successes, this exercise is one of those opportunities.

An online poster tried to validate his newly purchased MFJ-918 by measuring Insertion VSWR.

That is done preferably by measuring a good termination (dummy load) to validate that it has a very low VSWR, then inserting the Device Under Test (DUT) and measuring the VSWR as a result of insertion of the DUT.

The poster did not mention measurement of the dummy load alone, and it is a type that warrants validation.

Above is the poster’s test setup, his Rigexpert AA-170 is connected to the balun’s input jack using a M-M adapter. The output wires on the balun form a rough circle of about 550mm perimeter by eye. Continue reading Exploiting your antenna analyser #27

## Loss of windowed ladder line at MF/HF/VHF

A ham in the need of help recently asked for advice on eHam about the use of Wireman Ladder Line and the like.

After a fairly well considered, detailed and lengthy answer from on online expert, another online expert stepped in to confuse the matter with conflicting advice:

Wire resistance (loss due to current ) is not a factor with higher voltages typically seen in high impedance antenna feed applications. Attenuation loss is a factor depending on dielectric properties in VHF and UHF frequencies. Their is little skin effect below 50 MHz in wire antennas and feeds.

This comes down to line strength. I would go with the solid Copperweld for HF antenna work.

Let’s examine the above quote. Continue reading Loss of windowed ladder line at MF/HF/VHF