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Showing posts from 2023

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.   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 and a bias-T circuit, which is just the job for a weather sat.   Also see these:

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.  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 batches of antennas from any PCB factory, one needs to use high quality controlled impedance board stock . The side slots in this design increases the bandwidth a little, but it also reduces the operating frequency, so I'll have to see how it turns out and trim it. There is a variety of RF board made by various manufacturers ( Rogers , Isola , Panasonic ... ) and the RF parameters are different, therefore once you designed your spiffy new antenna for Rogers 4003C , then you cannot change your mind and manufacture it from Isola I-Tera MT40 - you need a new design. I therefore made a simple design in KiCAD and submitted it to three PCB manufacturers ( Eurocircuits, Ourpcb, Pcbonline ), to

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,