Month: June 2015

Review of Banggood digital clock kit

The Banggood large screen digital clock kit is an inexpensive kit (A$13 inc case and post).

The clock uses a DS1302 clock chip and microcontroller for display. The microcontroller is a STC15F204EA, a Chinese 8051 microcontroller.

Clock01

The kit is supplied with Chinese instructions, but a Chenglish version is available online. The only reason I needed an English version is to understand the somewhat obscure setting procedure, but the Chenglish version was not clear about the so-called “timekeeping” settings. Continue reading Review of Banggood digital clock kit

Last update: 6th June, 2015, 11:20 AM

VK3YE’s 3m circumference copper tube loop with RG213 stub tuning

Peter, VK3YE, describes a small transmitting loop (STL) in his video at https://www.youtube.com/watch?v=Cv_RnLpZ9gw.

? 100 watt 7 MHz magnetic loop for units and apartments - YouTube - Mozilla Firefox firefox 04/08/2015 , 07:24:25

As far as I can glean from the video, it is made from a 3m length of copper tube 19mm diameter, and uses about 1.8m of RG213 to tune it, and appears to have its centre 0.7m above ‘ground’ .

Let us firstly look at a free space model of the antenna using Reg Edwards’ RJELoop1 tool.

Screenshot - 07_06_2015 , 09_53_12

This model has its limitations, but the calculated inductance is of interest. We can calculate the inductive reactance to be 118Ω. The capacitive stub of RG213 will need around 107Ω reactance, and solving for RG213, we find that 1.94m gives 0.19-j107Ω. The resistive component is important as it is ignored by the above model. The stub resistance is a loss resistance, and we need to recalculate the efficiency. Efficiency=Rrad/Rloss=0.005/(0.19+0.0351+0.005)=2.17% (-16.6dB). We can also calculate the Q as 107/(0.19+0.0351+0.005)=465 and half power bandwidth as 7100/497=15.3kHz. Continue reading VK3YE’s 3m circumference copper tube loop with RG213 stub tuning

Last update: 4th August, 2015, 7:34 AM