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=Js*e^(-(1+j)*d/δ) where δ is the skin depth (δ=(ω*µ*σ)^0.5, σ is the conductivity).

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

Fig 1:

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

QRP quarterly on small transmitting loop efficiency

A correspondent recently wrote regarding the theory expounded in (Findling et al 2012), and their measurements and performance predictions of the AlexLoop Walkham, Portable Magnetic Loop Antenna by PY1AHD.

The authors give a formula for lossless Q (to mean no loss other than by radiation) without explanation or justification.

The formula is wrong, possibly a result of slavish acceptance of Hart’s two factor incorrectly applied (see Duffy 2015, and Antennas and Q). This error feeds into an optimistic estimate of antenna efficiency.

Analysis of measurement data

(Findling et al 2012) presents a table of measured half power bandwidth for the Alexloop.

Taking the 40m case, lets calculate to Q for a lossless loop, Qrad in Findling’s terms.

Note that Q for the lossless loop is about half that of Findling. Continue reading QRP quarterly on small transmitting loop efficiency

Workup of G5RV inverted V using high strength aluminium MIG wire

This article is a workup of replacement of my 2mm HDC G5RV and feedline with high strength 1.6 aluminium MIG wire to evaluate practical issues with use of an aluminium conductor.

The G5RV configuration is an inverted V, and although half a G5RV is 15m, the supports result in a 20m length of wire to the support. The configuration has a central support and simple spans for each leg of the G5RV to their respective supports. Continue reading Workup of G5RV inverted V using high strength aluminium MIG wire

DHT22 (AM2302) input for the generic heating / cooling controller

The generic heating / cooling controller (hcctl) is a flexible bang-bang thermostat controller based on an ATTiny25.

The project has been expanded to accept the Aosong DHT22 temperature and humidity sensor. The DHT22 produces a digital output (signed tenths of a degree) has a range of -40° to 80°, accuracy of about 0.5°, and 0-99.9% RH and costs a few dollars. hcctl can be configured for either temperature or humidity sensing (not both simultaneously).

Above is a development prototype with the DHT22 being heated by a small incandescent dial lamp to test function.

Continue reading DHT22 (AM2302) input for the generic heating / cooling controller