Posts Tagged ‘nerd’

New gadget measures negative resistance

If you are like me, you appreciate electronic gadgets with dials and displays. So when I discovered this “USB detector”,  I thought to myself that I really always wanted to know the voltage as well as the current consumption of my USB devices. And since it is more or less impossible to connect a multimeter, this is exactly what I need.

The device fully satisfied my curiosity. Actually one surprising result was that the charger for my Samsung Galaxy Note 8 has a negative output resistance.

With a load it outputs 5.27 Volts as shown in the top image. Usually one expects the voltage to increase when the load is removed. But for this charger the voltage dropped instead to 5.13 Volts (second image). That should mean that there is the equivalent of a series resistance of (5.13-5.27)/0.98 which is about -0.14 Ohm.

I measured other chargers also, without finding a negative output resistance, so it seems as if it applies to this particular charger only. Out of curiosity, I also measured the current consumption of my Arduino Mega to 0.08 A without any shields connects.

The unit has two outputs which are different from each other. Output 1 is a fully functional USB port, while output 2 only connects DC power. What is that good for? Well, the epanoroma blog opened my eyes to the utility of this. If you charge your phone at some public place, then this feature isolates the data port of your phone. That may protect you from being hacked.

So there you see. The €5.13 were well spent and I even learnt something new by giving in to the temptation to click “Buy It Now” on Ebay.

But why does the Samsung charger have what amounts to a negative output resistance, is it by design or by accident?

The radio amateurs are coming! Oslo Mini Maker Faire

“Have you dreamt about sending radio signals via the ionosphere? Or what about studying moon bounced echoes? Visit the radio amateurs and you can learn about analog and digital radio communications, antennas and electronics. There are 5-6000 radio amateurs in Norway, and they probably represent the oldest maker hobby.

This was the enthusiastic introduction that we were given on the web pages of Oslo Mini Maker Faire. It was arranged at Norwegian Museum of Science and Technology on April 6-7, 2013 in collaboration with the University of Oslo. There were close to 4000 visitors during the weekend and about 100 exhibitors. Our joint stand between the radio amateurs of the Asker/Bærum and Oslo clubs also had a constant stream of visitors.

LA8OKA at the stand (photo LA5FRA)

Our stand was only active on the first day, and it was manned by LA8OKA Martin, LA5FRA Paul Henrik, and LA9UTA Erlend in addition to me who served as the liaison to Oslo Mini Maker Faire since my employer, the Department of Informatics at the University of Oslo was a sponsor of the Faire. There was also a good deal of curious radio amateurs that stopped by during the day.

We had a couple of Elecraft K2’s, several home-brewed electronics projects, the possibility to send your own name in Morse code, and several posters that covered everything from emergency communications and APRS to radio amateurs on the space station.

LA8OKA explaining the innards of the K2

We also had a 0.15 W WSPR transmitter that we had hoped could transmit out through one of the large windows. The intention was that we could follow its reports on the internet, but there turned out to be too much metal in the window frames and the curtains so radio waves would neither enter nor exit – whether it was HF, VHF, or GPS-frequencies. Therefore we ended up explain the fascinating aspects of radio propagation from posters instead.

There was much interest in our stand, and many expressed that they found ham radio to be exciting. Several were also interested in ham radio courses. Among pan cake robots and other robots, 3D printers, Star Wars-enthusiast, computer gamers, 3D photo, advanced Lego builders and Norway’s largest smoke ring canon, this was finally a place where people like us with as nerdy an interest as radio felt quite normal.

Trying out Morse,
in the background a 3D printer

This was therefore a perfect place for radio amateurs to take part and since it most likely will be arranged again we should be prepared to take part next year also.

The radio amateur who felt compelled to abandon his own call sign

If you mention that you are a radio amateur to any Norwegian who was old enough to watch TV in the mid 70’s then he is bound to respond with LA8PV. This was the callsign of the fictious figure Marve Fleksnes in the comedy the “Radiot”. To bad for the poor guy who actually was given that callsign some years later. I had contact with him on CW (= morse) in 2002 just after I got my license and I just couldn’t believe that anybody actually was using that particular callsign.

It was in 1976 that Rolv Wesenlund (1936 – 2013) one of Norway’s most popular comedians, played Marve Fleksnes. As radio amateur LA8PV he talks with his friend JA1NQ in Japan. He also speaks with TF3XU on Iceland in a mixed Icelandic/Norwegian dialect which is always a hit with a Norwegian audience. He then converses with Norwegian/American WONBF (no zero) in Minnesota. He has to handle his angry neighbor who suffers from interference (RFI) and finally LA8PV gets the opportunity of a lifetime when he hears the emergency call, Mayday, in the 15 meter band.

The first of three cuts can be viewed in the embedded Youtube video. Unfortunately I couldn’t find any clip that was subtitled in English, but the first minute or so is almost silent and is about the joy of getting a replacement DF1987B (sic) tube for his transmitter. The tube is supposedly plugged into the output tube socket of a Quad II audio amplifier and then he is ready to go on the air. Later one gets a glimpse of his AR88D receiver.

As the story goes, the Norwegian Post and Telcom Authorities, had marked off LA8PV as a callsign that shouldn’t be used. But due to a mistake they blacklisted LA8PW instead. I had contact with LA8PV almost every year up to and including 2007, but have never had it since. I understand why now, because says that the real LA8PV finally must have given up and gotten the new call sign, LA2WRA, on 4 Jan. 2008. I don’t envy him the fate of having been made LA8PV, and fully understand why he finally abandoned that callsign.

The source for much of this story is a Swedish discussion page on Marve Fleksnes and LA8PV also aired on Swedish television and were very popular there as well.

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