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Showing posts from February, 2020

Phased Array Antenna for 5 GHz Band

I've been toying with a switched phased array antenna design for use on a small aircraft.  This type of antenna could be made to radiate forward, backward, or to the sides.  With the addition of a Raspberry Pi Zero (or Arduino Teensie ), a UBlox GPS receiver and 4 little RF switches, your toy aircraft could then always point its antenna towards your ground control system, without using any step motors or moving parts - well, except for the armatures of the little RF switches. Phased Array NEC2 Simulation The design is essentially four Yagi antennas positioned back to back in a cross.  Only one dipole is driven at any time and the result is that the rearward parasitic elements act as a reflector for the antenna that is active.  This improves the front to back ratio quite noticeably.  The NEC2 graphs show extremely small back and side lobes, which I found so encouraging, that I went ahead and built the ant

Yagi Antenna for 900 MHz ISM Band

I like tinkering with wire antenna designs, since they are simple and cheap to make.  Mr Yagi invented his antenna about 100 years ago, but there are still some things left to learn about it. 900 MHz ISM Band Yagi The 900 MHz ISM band ranges from 902 to 928 MHz.  Covering the whole band with a single Yagi antenna is difficult, since they are inherently narrow band devices.  Consequently some tweaking is required and the result below is a desensitized design that can be built and replicated quite easily, but you need a network analyzer - "To Measure, is to Know!" A Yagi generally consists of a Reflector, Radiator and one or more Director elements, arranged on a boom.  For a small Yagi, a wooden ruler works a treat, since one can easily mark the position of the wires.  The wire elements are fastened to the bottom of the ruler with hot glue.  The wire elements are  made from straightened out jumbo size paper clips.  The balun, is two clip-on Ferrites, to preven

KiCAD Schematic and PCB Design

The venerable Eagle PCB design program has gone Cloudy .  I have used  Eagle for about 20 years - sometimes I bought the professional version and sometimes I just used the free hobby version - depending on what I needed to do.   Eagle now requires a permanent subscription, which is not compatible with intermittent use . I therefore looked around for a Free PCB design program, tried gEDA PCB and KiCAD and quickly found that I am not alone.  My favourite high tech toy stores Sparkfun and Digikey also looked around and we all settled on KiCAD .  It turned out that KiCAD is also used by Great Scott Gadgets (HackRF One) and that two of the main developers of KiCAD are employed by CERN . KiCAD on a MacBook If KiCAD is good enough to make the HackRF One PCB, then it must be good enough for me... As with all CAD tools, it takes a little getting used to.  Note that Move and Drag are not the same.  For example, Dragging will rubber band the wires, while Moving will not. I t