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
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.
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.
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).
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.
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.
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.