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

Effect of shorting turns on a tapped air cored solenoid at RF

The roller inductor in a Palstar AT2K will be taken as an example to illustrate the technique. This tuner is popular and has a very good reputation amongst hams, though (Duffy 2012 was less enthusiastic).

Above a pic of the internals of the AT2K. The unused roller induction section is shorted. Continue reading Effect of shorting turns on a tapped air cored solenoid at RF

NodeMCU devkit V1 deep sleep

Low cost implementations of the NodeMCU devkit V1.0 abound on eBay, and are featured in lots of projects.

Deep sleep mode is used in a lot of projects, the MCU is but into sleep mode and it requires circuitry so that the  from the /WAKE pin (D0, GIO16) can pull the /RST pin to wake the processor up.

The problem

The common schematics as above simply wire /WAKE pin (D0, GIO16) to /RST (yellow wire), but this disrupts operation of the reset circuit, which degrades development productivity. Continue reading NodeMCU devkit V1 deep sleep

ESP8266 IoT DHT22 temperature and humidity

This article documents a first project with the Espressif ESP8266.

The objective is a module that will take periodic temperature and humidity measurements and publish them to an MQTT message broker.

This inital implementation is very basic, it is largely configured in code, though it does use DHCP. Later extensions might include a web interface for configuration of WLAN parameters etc, but for the moment the emphasis is assessment of reliability given some reports on the ‘net.


A module was purchased with on board CP210x USB to serial chip. The only other component needed was the DHT22 digital temperature and humidity sensor.

NodeMCU was chosen for the ESP2866 firmware because of the inbuilt support for ‘interesting things’, including the DHT22.

Above is a breadboard of the system for development. Continue reading ESP8266 IoT DHT22 temperature and humidity

Review of Dodd’s WSPR based antenna comparison

Dodd espoused the merit of WSPR for antenna comparison in his article (Dodd 2011).

He documented a series of WSPR spots of his transmitter on 20m in a table swapping between antennas during the test period, one side of the table for each antenna. (Don’t be misled, the dipole is not half wave dipole but some non-descript multi band loaded dipole.)

He calculates the average for each data set and states:

The average from the dipole and the loop -16.74 and -17.0dB respectively meaning that the performances were very similar.

You might reasonably interpret this to mean that there was no significant difference between the antennas, one was as good as the other. Continue reading Review of Dodd’s WSPR based antenna comparison

Review of 5 months of iiNet Internet access

On 5/10/2016 we cut over to a new Internet access service, switching from Telstra 8Mb/s ADSL to iiNet NBN 12Mb/s.

Over some years, I have run an automated file transfer to measure the speed of our access service. The tests are done between 6:00 and 22:00, I am interested in performance during the times I want to use the service, and less interested in times when I would usually be sleeping.

Above is a graph of yesterday’s performance. Note that the service does not delivery anything like the 12Mb/s description of the service, and it collapses in the evenings when IP television demands exceed the network’s capacity.

Above is a chart of the tests over the previous week… the collapse in the evening is common. Continue reading Review of 5 months of iiNet Internet access

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.

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)