For some years I have used Ceramica muffin fans for low noise and long life. They use a ceramic bearing which is quieter than ball bearings, but longer life than sintered bronze bearings which dry out.
In the last month, I have replaced three Ceramica fans that have failed, one with less than a year’s service and two with less than one month’s service. Continue reading Review of Ceramica ceramic bearing fans
For some years I have used Ceramica muffin fans for low noise and long life. They use ceramic bearing which are quieter than ball bearings, but longer life than sintered bronze bearings which dry out.
That said, I was annoyed to find the fan I have replaced in a one year old computer power supply fail after another three years. The original was a bronze bushed fan which dried up. Continue reading Fan frustrations
Much is written about the virtues of some types of coax connectors over others.
Continue reading Coax connectors and accurate / repeatable measurements
![icah4e04[1]](https://owenduffy.net/blog/wp-content/uploads/2014/03/icah4e041.jpg)
TuneMate is an accessory for Icom radios to make tuning an external ATU faster and more convenient. Continue reading Tunemate update
I purchased a Bushnell Back Track D-TOUR, partly because it appeared to have a useful digital compass.
The digital compass turned out to be a major disappointment . The documented calibration procedure made little difference, it was still commonly more than 10° in error (not due to nearby magnetic objects, or T/M variation).
A common method of making Noise Figure measurements of a receiver is to use a noise generator of known noise power. The output power of the DUT is measured with the generator off (NoiseLo) and on (NoiseHi), a Y factor calculated, and from that Noise Figure is calculated.
Continue reading Using an attenuator for NoiseLo/NoiseHi in NFM
Above is a clip from W4HBK’s 40m grabber today, the signal is VK2OMD running 5W QRSS6 over a 14,700km path. We can infer (Duffy 2012b) from the 15dB S/N in that capture in 0.25Hz noise bandwidth, that in an 800Hz CW filter for say -5dB S/N (threshold of copy) we need 15dB more signal, or 160W for reliable copy. (Less power may be adequate for very short QSOs at the peak of fade cycles.)
Continue reading Simple Morse beacon keyer updated 2014/03/01
There is a risk of damage when flashing ESCs. It accrues from the fact that ESCs have a three-legged H bridge and if a high and low FET are turned on simultaneously, damaging currents may flow. In fact, this can be an issue if the FETs are on together for just microseconds on each PWM cycle. Loading the wrong hex module is a recipe for disaster, it may turn on FETs in an unexpected way.
So, for safety, the ESC should be powered from a current limited power supply during flashing and initial motor testing.
In a process of continuing development, this article describes a variation on the inexpensive current limiter for flashing and initial testing of ESCs – Mk I.
Continue reading An inexpensive current limiter for flashing and initial testing of ESCs – Mk II
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.
There is a risk of damage when flashing ESCs. It accrues from the fact that ESCs have a three legged H bridge and if a high and low FET are turned on simultaneously, damaging currents may flow. In fact, this can be an issue if the FETs are on together for just microseconds on each PWM cycle. Loading the wrong hex module is a recipe for disaster, it may turn on FETs in an unexpected way.
Continue reading An inexpensive current limiter for flashing and initial testing of ESCs – Mk I