Skip to main content

Posts

Weather Satellite VHF LNA

Minikits in Australia ( https://www.minikits.com.au/ ) 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 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 and a bias-T c
Post a Comment
Read more
Recent posts

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, low loss, 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, Pcbon
Post a Comment
Read more

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 https://www.adsbexchange.com/ 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
Post a Comment
Read more

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,
Post a Comment
Read more

Aye Eye Bed-Time Story Generator

Machine Learning is used for various hard practical problems, such as the safe control of autonomous cars that have to navigate a cluttered and dynamic environment, without bumping off cyclists and running over old people trying to cross a village road.   There are also other more entertaining uses for it, such as the creation of bed-time stories for your grand children.  ( Yup, I'm that old.  I started learning programming FORTRAN on a Univac with punch cards, eh.  Now get of my pennisetum clandestinum... :). Go to OpenAI ChatGPT and make yourself a free account: https://chat.openai.com/auth/login Let the fun begin:   Write a short story for ten year olds. Scary government people created a video of a moon landing and will catch you if you deny it. Give the protagonist two buddies with distinctly different personalities. Result: Once upon a time, there was a young boy named Jack who loved watching the stars at night. He dreamed of one day becoming an astronaut and exploring t
1 comment
Read more

Let There Be Light

I made a ceiling light fixture for my workshop ( it is supposed to be my garage ) from scrap wood.  Since LED lights do not get hot, one can do that without danger of burning the house down, but it would be a good idea to incorporate a 250 mA polyfuse in there for peace of mind.   The light of my life. To hide the ceiling house wires and chocolate block connector, I made a big hole in one block with a hole saw and glued it to another block.  The vertical stick is mortised into the ceiling block - rubbed some wax on it all and there we have a little Tinkertoy Chandelier.  I used bees wax, but good old boot polish will work as well and it comes in multiple shades. Cantilever Desk Lamp BTW, the easy/lazy way to make a rectangular mortise hole, is with a drill and a jigsaw.   You just slowly grind the wood away with the saw blade till you have a perfect fit.  A hammer and chisel does not work well on soft wood, no matter how sharp the chisel, while a jigsaw will happily chew up anything! I
Post a Comment
Read more

Wooden Post Thumper

We planted a new tree and wanted to stabilize it with three posts, so it won't blow over in a storm, while it is still young.  It turned out that planting the tree was the easy part.  Hammering the 2.5 meter support posts into the ground, was a whole 'nuther problem. One cannot use a sledge hammer on a tall post, since climbing onto a ladder and swinging a heavy weight around, two meters above ground, is sure to cause a rapid, unplanned descent from the ladder. The safe solution is a pile driver - a heavy pipe that is closed at one end. I could not find a pile driver at the local hardware store and in any case it would cost around 65 Euro, so I took some scrap wood and a two hundred year old sledge hammer and there we go.  The only expense was a handful of screws.   The thumper works remarkably well.  It took longer to make the thumper than to set the three posts, but now I can also use it to drive in a sand point shallow well for the garden.   Start with a 15 cm piece of a sq
Post a Comment
Read more