eBay charger adventures: Joke or scam?

Because modern smartphones are really battery eaters, you decide to look at eBay for a car charger, just to charge a bit your battery while driving with the hope to extend battery life at least until you get home.

Smoke from Imax B6 charger

This is the history about an Imax B6 charger who was used to charge a large 15Ah Li-ion battery. Because of the large battery capacity, the charging current was set to the maximum the charger is capable: 5 amps.

The charger was able to charge the battery nicely four or five times, but the next time, the charger went into fire and smoke.

Linux and the future of desktop

These days I have been reading articles and opinions in the net about the new Windows 8. Why? Because Windows 8 is the starting of the end of the desktop as we know it. Windows 8 is the first step in Microsoft roadmap to unify all the current platforms (Home computers, tablets and phones) into a single interface.

But using the same interface into so very different devices means you can only use the lowest common denominator of all of them, in this case, phones. And this also means you must use your desktop computer in the same way you use your phone.

24GHz the old way

In the 80's wide band FM was common in the 10 GHz band. When 24 GHz devices were available at surplus, wideband FM was overridden by narrow band modes (SSB), so there was very little wide band FM activity at 24 GHz. Even today there is almost no wideband activity in any microwave bands (Except for some ATV signals). Why?

Dissection of Icom FA-S6270A antenna

In this photo you can see a dissection of a quad band Icom FA-S6270A rubber antenna who suddenly stopped working:

This is the antenna supplied wit the Icom IC-T81 quad band walkie talkie. The symptoms were very evident: The antenna suddenly become deaf, giving very poor signals, so it was sacrificed in the name of science.

Looking for the Square Law region (II)

After the experience in Looking for the Square Law region (I) it was clear the only way to find the Square Law region was to find a way to measure microvolts. The first idea was to use an operational amplifier in a DC non-inverting amplifier with a gain of 1000 (actually 1001). This will allow me to measure microvolts as millivolts. My first try was a OP07, but input bias currents were too high, so I ended using a JFET operational amplifier, a TL081.

Looking for the Square Law region (I)

One of the basic tasks in RF work is to measure power. There are many ways to measure power but the simplest ones use a diode as peak rectifier. Peak voltage (over a known impedance) is a measure of power, because P = (V_eff)² / R and V_eff = V_peak x √2. Combining both expressions you get P = (V_peak)² / 2R, where R is usually 50 ohms.