Category Archives: Technology

The Kilogram

So I thought I knew what a kilogram was until I read this.

Photo: Robert Rathe/National Institute of Standards and Technology

Once a year, three officials bearing three separate keys meet at the bottom of a stairwell at the International Bureau of Weights and Measures, in Sèvres, France. There they unlock a vault to check that a plum-size cylinder of platinum iridium alloy is exactly where it should be. Then they close the vault and leave the cylinder to sit alone, under three concentric bell jars, as it has for most of the past 125 years.

“So what?” you say.

The trouble posed by the master kilogram is apparent in the many friction-filled steps by which it calibrates other masses. Once every few decades, a scientist plucks the cylinder from its perch with chamois-leather-padded pincers, rubs its surface with a cloth soaked in alcohol and ether, and steam-cleans it. Then he puts the prototype in a precise balance that compares it to the bureau’s official copies, which are in turn compared to copies kept by member countries. And thus the prototype’s mass trickles down to set the standard for the rest of the world.

The system has been far from seamless. When the cylinder was last removed from the vault in 1988, the bureau’s metrologists were disappointed to discover that its mass and those of its official copies had drifted apart by as much as 70 micrograms since 1889. That discrepancy is tiny—comparable to the mass of a small grain of sugar—but it confirmed a troubling instability. All that metrologists can say is that the master kilogram seems to have lost as much as 50 µg over the course of a century relative to its siblings. But the actual drift could be up or down, and it might even be a lot more than 50 µg, because the prototype and its metallurgically identical copies could all be changing as an ensemble.

It is a long article, but worth a read.


We all have an interest in the weather to some level or other.  I finally cracked earlier this year and got a weather station, a Davis Vantage VUE with a Weatherlink USB interface.

Unfortunately, not long after I got it the humidity and temperature sensors inexplicably failed. So back to Weathershop, and after a fairly quick turnaround, it has been working fine all Summer.

This weekend, the good weather co-incided with me being at home.  So, with permission from SWMBO, the drills came out, and the sensor suite is now mounted in a reasonable location off the gable end of the house (it was in the garden up to now).

The data is available online, using the wview package. It is also available at or findu, as, being into APRS, I’m feeding it into the APRS-IS backbone and contributing to the Citizens Weather Observation Program.


KX1 #2213

So, the Rugby World cup is over, Vettel has won another Grand Prix, it’s a bank holiday Monday and it is raining buckets out. What do to? Press play on Soldersmoke 137, fire up the soldering-iron and finish building a KX1 of course.


I didn’t get a chance to test it on-air yesterday as my 20m dipole is down and it was too wet to put something up temporarily, but it seems to be working ok into a dummy-load. Next up are the KXAT1 Automatic Antenna Tuning Unit and the 30m/80m module.

Hmm, I wonder.

One day, at the start of the summer (?), I was looking at some of the aerials on our building and wondered what the spectrum was like around the TSSG building in Carriganore, and indeed Waterford City.

I quickly threw together some scripts to see if the Spectrum Analyser could gather the data, which it could relatively easily. We had several students on work placement and I asked Patrick to look at writing scripts to process the data generated by the analyser.

Here is an example of a weeks worth of results in the Civil Aircraft band.


Waterford airport ATIS isn’t as strong as I would have expected on 121.150MHz, however the site is shielded in that direction.  All the results are shown here.

I think, at some stage,  we will go back and re-do some of the bands with less attenuation, this should allow us to see much more detail down in the ‘grass’. This might let us see more detail in the UHF TV bands as it seems quite sparsely populated.