Tuesday, October 30, 2012

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?

Monday, October 22, 2012

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.

Tuesday, October 9, 2012

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.

Sunday, October 7, 2012

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 = (Veff)/ R and Veff = Vpeak x √2. Combining both expressions you get P = (Vpeak)2 / 2R, where R is usually 50 ohms.