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Showing posts from 2024

Wide Band Aerials For 1700 to 2400 MHz, M1 - M6 Band

The 1700 to 2400 MHz band (M1 to M6) is a good band for the secondary control channel of air and ground robotic vehicles.  Little radios made by Doodle Labs in Singapore are popular and this is an antenna solution specifically aimed at the Meshrider radios ( ). I employed Ye Olde Fashioned technique of carving an antenna out of double sided board with a ruler and a scalpel, using copper tape for little optimization experiments and fixing the mistakes.  Once one has the hang of it, it is possible to carve an antenna by hand in a day, vs waiting two weeks for a PCB factory.   Etching it is good, if you have the chemicals and safety paraphernalia on hand and know what you are doing. This application requires an aerial system with a few important properties, notably: Wide bandwidth of 20% or more with a centre frequency of 2 GHz. Directivity of 8 to 12 dBi, to reduce clutter and interference from the surroundings, without making it

OpenEMS with Octave and SciLAB

I wanted to do some advanced RF antenna development work and needed an electromagnetic field solver that is a bit more up to date than NEC2 .  Commercial solvers from Matlab , Ansys and others are hideously expensive (in the order of $20,000 to $50,000) and do not fit in the wallet of a hobbyist or a small consulting company.  Recently, openEMS became available and it fills the niche with a capable free tool.  In general, openEMS is a solver - a Finite-Difference Time-Domain (FDTD) numerical engine.  You interact with it through Octave , which is almost identical to Matlab .  You can watch a good video by Thorsten Liebig here:   Getting it to work is a little painful, but it is free, so bear with it - then save a backup clone, or a zipped copy of the whole virtual machine directory and NEVER update it, to ensure that it keeps going and doesn't get broken by future updates, right when you are in the middle of somethin