## Enhancement of Calculate small transmitting loop gain from bandwidth measurement

At Efficiency and gain of Small Transmitting Loops (STL) I explained an approach to assessing the gain the efficiency of STL, and provided a link to a calculator to perform the calcs.

This expands on application of the concepts and introduces an enhanced calculator to perform the calculations.

Firstly, this technique applies to antennas where the VSWR characteristic is consistent with a feed point or virtual feed point where around the frequency of minimum VSWR, X varies with frequency much more than R. The simplified analysis assumes that R is constant, and change in X is the reason for the VSWR characteristic. See VSWR curve of a simple series resonant antenna for more information. Continue reading Enhancement of Calculate small transmitting loop gain from bandwidth measurement

## Review of inexpensive Chinese thermostat – MH-1210

This is a review of an inexpensive MH-1210 Chinese bang-bang  thermostat that was purchased on eBay for around A\$13 complete with thermistor sensor and postage.

Above is the thermostat. Note that the middle terminals, the 230VAC power input terminals are labelled ONLY in Chinese. Continue reading Review of inexpensive Chinese thermostat – MH-1210

## VK3IL’s 3m circumference LDF4-50B loop on 40m

David, VK3IL, describes a small transmitting loop (STL) at Portable magnetic loop antenna.

As far as I can glean from the article, it is made from a 3m length of LDF4-50B Heliax, and uses a Patterson match to tune it.

David offered measurement of VSWR around centre frequency for the loop matched on 40m. He has measured the VSWR=2.6 (the half power) bandwidth shown between markers 2 and 3 to be 22kHz. Continue reading VK3IL’s 3m circumference LDF4-50B loop on 40m

## Review of Banggood digital clock kit #2

At Review of Banggood digital clock kit I wrote some comments on the Banggood large screen digital clock kit.

As noted, the supplied instructions are in Chinese, but a bit of searching turns up Chenglish instructions on the net (https://www.dropbox.com/s/fb68yokgwvfx7ye/SKU142210%20instruction.pdf).

The reference to “whole point timekeeping” escaped me, but after more searching, it appears to be the result of conversion of Chinese to English… English speakers might know the facility as “hourly chime” where the clock chimes (emits a sound) at the start of each hour, in this case 3s of beeps. Continue reading Review of Banggood digital clock kit #2

## Cooling an IC2200H – update

I have an IC2200H mounted on my operating table with 25mm clearance above the radio and ample room for convection currents to assist in heat removal. It is concerning that the case temperature reaches temperatures that are not safe to touch, temperatures in excess of 75° (55° above ambient) have been measured and that has not triggered the internal temperature protection… so it could get hotter still!

Whilst it might take a while for the radio to reach high temperatures, in the long term, it must dissipate around 139W when transmitting on HIGH power setting and at ambient temperatures as high as 35° in the shack. (Rated input is 15A at 13.6V for 65W out, leaving 139W of heat to be dissipated.)

This is one of those high power mobile radios that advertises no fan as an advantage, but it is clearly not up to the task!

The objective of this change is to keep the external parts below 60°, the (ASTM standard C1055  1999) 5 second human skin burn threshold.

## 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.

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

## 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.

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.

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

## Dodgy Chinese thermocouple thermometer

I purchased an inexpensive two channel thermocouple thermometer on eBay. It was very low cost (A\$24 inc post) so there was risk that it was low quality and since cost of returns is so high, that it was wasted money.

## But it was junk…

In fact, it did turn out to have a major problem. Continue reading Dodgy Chinese thermocouple thermometer

## A test run of the generic heating / cooling controller with 10k NTC thermistor sensor

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

The test load is a pot containing 1l of water and a 1200W immersion element controlled by the SSR above (on-off control). The controller board is a ‘fully optioned’ test framework, hcctl is the left hand DIP8 and the other is a TC427 H bridge (not needed for this SSR which can be driven directly from the ATTiny25 output pin) for buffered output and alarm. Continue reading A test run of the generic heating / cooling controller with 10k NTC thermistor sensor

## 2.4:1 balun design failure

A lost soul searching for enlightenment on impedance transformation sought advice on a transformer at 2.4 : 1 BALUN.

Inevitably one of the forum experts counselled:

Assuming your quad is a single-band HF antenna, a conventional transformer using #2 powdered iron would be my choice for the balun function. The reactance of the secondary winding would need to be at least 600 ohms.

So, let’s put the forum expert’s advice to a practical test.

## Fleshing out the proposed solution

I have at hand a T200-2 core, so lets calculate the secondary turns to satisfy the proposed solution.

Above is calculation from a popular online calculator. For 14MHz, the secondary should be at least 23.8t. We will use 24t. Continue reading 2.4:1 balun design failure