June 2015 – Page 2 – owenduffy.net

Capacitive loading device for fine tuning wire dipoles

There are applications where you might want to make the tuning of a wire dipole adjustable.

Adjusting the length is often not convenient, especially in-service tuning which might be triggered by changing vegetation, ground moisture etc.

This article shows some simple means of attachment of a small capacitive load to deploy near the high charge points, and to adjust their effect by moving them to or fro on the main dipole wire. Continue reading Capacitive loading device for fine tuning wire dipoles

Last update: 16th June, 2015, 11:52 AM

Capturing the AVR hex file built by Arduino on Windows

One often sees enquiries by people trying to save the hex file made during the Arduino build process.

It is not trivial, as in their wisdom, Arduino hides these details, and builds the hex file in a randomly named temporary directory for each IDE which it deletes when the IDE is closed.

There are times when you may want to save the hex file, perhaps to load it without a bootloader or using a non-supported bootloader, Flashing LED driver using an ESC was just such a project. Continue reading Capturing the AVR hex file built by Arduino on Windows

Last update: 31st October, 2015, 8:17 AM

Review of inexpensive Chinese thermostat – 8010F

This is a review of an inexpensive 8010F Chinese bang-bang thermostat that was purchased on eBay for around A$13 complete with thermistor sensor and postage.

Above is the front view of the thermostat. There are many thermostats on the market with similar front panels, but they differ in internals and most importantly, performance and quality.

Above, the rating label is clear and informational. It is rated at 10A for resistive loads (AC-1), but it is doubtful that AC-3 motor loads of more than 20-30% of that should be used. Continue reading Review of inexpensive Chinese thermostat – 8010F

Last update: 1st March, 2019, 8:26 AM

Cooling an IC2200H – update #2

I have described a solution an overheating problem with my IC2200H at Cooling an IC2200H.

Another solution for control of the fan to minimise nuisance draft and noise is one of the inexpensive digital thermostats on eBay.

I reviewed one of these things at Review of inexpensive Chinese thermostat – MH-1210. It had its issues, but as modified for 12VDC operation, I tested it for control of the fan in the above pic.

Above is the thermostat, though modified, purchased for about A$12 including post and the sensor thermistor. Don’t buy the MH-1210 as some at least are shipped with incorrect calibration. Continue reading Cooling an IC2200H – update #2

Last update: 12th June, 2015, 4:46 PM

VK3IL’s 3m circumference LDF4-50B loop on 20m

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

At VK3IL’s 3m circumference LDF4-50B loop on 40m. I reviewed his loop behaviour on 40m, and its efficiency was quite low… though typical of a loop of that size at that frequency.

Radiation resistance of a STL is proportional to the fourth power of frequency, and since it is often dwarfed by loss resistance, we should expect that doubling frequency will dramatically improve performance.

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 approximately matched (VSWR=1.24) on 20m. He has measured the VSWR=2.86 bandwidth shown between markers 2 and 3 to be 45kHz. Continue reading VK3IL’s 3m circumference LDF4-50B loop on 20m

Last update: 12th June, 2015, 9:20 AM

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

Last update: 13th June, 2015, 8:17 PM

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. It is rated at 10A for resistive loads (AC-1), but it is doubtful that AC-3 motor loads of more than 20-30% of that should be used. Continue reading Review of inexpensive Chinese thermostat – MH-1210

Last update: 1st March, 2019, 8:26 AM

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

Last update: 12th June, 2015, 9:20 AM

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

Last update: 10th June, 2015, 1:22 PM

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.

Continue reading Cooling an IC2200H – update

Last update: 27th June, 2016, 12:28 PM