Skip to main content


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

The 1700 to 2400 MHz band (M1 to M6) is a popular 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 i
Recent posts

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

Earth Observation Satellite 1700 MHz Patch Antenna

The L-Band is carved up for many services and the 1690 to 1710 MHz Space to Earth band is shared with 4G cell phone services, with several geo stationary and polar orbit earth observation satellites operating at 1702.5 and 1707 MHz .  Since I recently made an ADS-B 1090 MHz patch I decided to make one for this higher frequency band, while I am still in the swing of things with my mad antenna carving skillz . This Right Hand Circular polarized antenna is carved from Rogers RO4350B low loss PCB and after a couple days of meticulous cutting and measuring it is spot on. It is amazing what one can make if one has enough coffee, chocolate and patience! Rogers 4350B copper clad circuit board has the following RF parameters: Permittivity Dk = 3.66 Loss Df = 0.0031 Dielectric width Dw = 0.508 mm Cu 1 Oz = 36 um This Joint Polar Satellite Service (JPSS) antenna has the following dimensions: Base: 69 x 54.6 mm Patch: 53.3 x 43.4 mm Corners: 12 x 12 mm Slots: 5 x 8 mm Feed: 1.1 x 7.5 mm A r

Weather Satellite VHF LNA

Minikits in Australia ( ) makes a nifty little low noise RF amplifier for a VHF weather satellite receiver, such as the Meteor satellite on 137 MHz.   Note that SatDump is very much improved now - it is all the software you need to see that it is raining outside, without the stress of looking out the window. Some careful soldering is required, but it is not difficult to build. When I test an RF circuit, I run it from a 12V sealed battery - my noise free power supply . Once tuned up carefully with a nylon screwdriver ( the little spatula that you get with epoxy glue! ), it can provide up to 20 dB gain, but on average over the band, expect about 5 to 10 dB.  With some patience I eventually managed to eek out 7.6 dB at 137 MHz .  This may not sound like a lot, but a radio receiver is more dependent on the Signal to Noise and Distortion Ratio ( SINAD ), than the actual signal level. The LNA is a tuned single transistor amplifier with a linear power supply a

ADS-B Patch Antenna on RF Controlled Impedance PCB

In a moment of boredom/inspiration, I thought about making a patch antenna for my ADS-B aircraft tracking system, which is part of ADS-B Exchange .  One can make one-off patch antennas from garden variety glass/epoxy FR4 board, but the result will have relatively high loss and it will not be repeatable.  In order to simply order high quality batches of antennas from any PCB factory, one needs to use low loss, controlled impedance board stock . With this antenna, the ADS-B receiver simply sits on my window sill and picks up aircraft 200 km away. Cut Corners The design is a typical rectangular patch antenna, with circular polarization.  A circular polarized antenna allows more mounting options for a conformal antenna. Slots The side slots in this design increases the bandwidth, but it also reduces the operating frequency, so slots can be used to tune a patch antenna design. Board Type There are a variety of RF boards made by various manufacturers ( Rogers , Isola , Panasonic ... ) and

ADS-B Quarter Wave Whip Antenna

I reclined in the winter garten nursing my back and watched a gaggle of geese and aircraft soar overhead, which made me realize that it's been a while since I made an Air Traffic Control (ATC) antenna, so I dug in my Junque Bochs for an old Raspberry Pi v3, a RTL-SDR dongle and a tripod telescopic test antenna , downloaded the latest ADS-B ( Automatic Dependent Surveillance-Broadcast ) decoder image from and went to work play. The last time I worked with ADS-B transponders was maybe five years ago, when I used a RTL-SDR to test a Sagetech Mode-S ATC transponder and the free decoder software has improved dramatically since then.  It took about an hour to set the system up and I could immediately see a handful of aircraft, as far away as 80 nautical miles (150 km), using a wonky little telescopic antenna on my office window sill. After a while I captured an Emirates A380, a USAF Galaxy and a Slovak AF LET 410 Turbojet from the military airport nearby

To C or not to C, That is the Question

As most would know, the Kernighan and Ritchie C Programming Language is an improved version of B, which is a simplified version of BCPL, which is derived from ALGOL, which is the Ur computer language that started the whole madness, when Adam needed an operating system for his Abacus, to count Eve's apples in the garden of Eden in Iraq.  The result is that C is my favourite, most hated computer language , which I use for everything. At university, I learned FORTRAN with punch cards on a Sperry-Univac, in order to run SPICE, to simulate an operational amplifier.  Computers rapidly lost their glamour after that era! Nobody taught me C.  I bought the book and figured it out myself. Over time, I wrote a couple of assemblers, a linker-locator, various low level debuggers and schedulers and I even fixed a bug in a C compiler - not because I wanted to, but because I had to, to get the job done!   Much of my software work was down in the weeds with DSP and radio modems ( Synchronization,