SatNOGS part IV – the v dipole antenna

So we come to the final instalment of my current journey along the highways & byways of satellite observation and bring my story up to date. After the disaster that was the QFH antenna I stumbled across this post whilst searching for possible fixes, outlining a simple dipole build. “It can’t be this simple!” I thought to myself, after all the effort I put into the QFH build and now someone’s telling me I can get results with 2 short lengths of aluminium rod! Desperate to get my observation station back online I invested in a couple of 1m lengths of 4mm dia aluminium rod from the local B&Q (I had everything else I needed already) and set about the really simple build. The part that took the longest was the 3D printing of the mast mount.

The images below sum up how easy the build was …

Ironic how the longest post was about a failed antenna build and the shortest post about a successful one! I’m thinking of investing in a low noise amplifier next … after that I may look into a directional antenna assuming I have room to site it in my back garden (I’m thinking possibly not but it warrants further investigation).

Finally, my ground station is named MerCre1 (not too hard for those that know me to work out how I came up with it, plus I think it sounds a little like a name you’d give to a satellite 🙂 ). If anyone feels the urge to check out my observations on SatNOGS you can find me here.

A couple of people have asked about source files for the mast mount. I’ve created a zip file containing the original FreeCAD design file plus the STL & GCODE files, please feel free to download it here.

Thanks for reading, hopefully I’ve tempted 1 or 2 of you to join the fold.

SatNOGS part III – the QFH antenna

And so begins the bitter sweet tale of Merv’s QFH antenna build … hang on in there until the end to find out why. By the way, I am in no way an expert in any of this. I am a complete noob so please feel free to leave a message if I’m talking rubbish anywhere in the post and I’ll get it corrected.

As you’d expect, there is a ton of useful info on the SatNOGS wiki pages. I’d recommend hitting the first menu option at the top of the page for their Build articles.

After a few observations of various satellite passes and delving into the SatNOGS forums to get a better understanding of what’s what I decided it would be interesting to capture the transmissions of the NOAA weather satellites. They are polar orbiting and pass North-South which fits in nicely with my urban location so I started searching for a suitable stationary antenna design (as opposed to a tracking antenna which is basically controlled by motors such that it can follow the satellite as it travels across the sky … this could be one for the wish list!). The design that kept appearing in my searches was the QFH or Quadrifilar Helix antenna … basically it promised excellent horizon to horizon gain (where you need it most as the distance from satellite to antenna is at its greatest) and minimal signal loss vertically (when the satellite is overhead and at its closest).

After much reading I plumped for the design from this site … disclaimer, without wanting to reveal the outcome of this endeavour, in no way am I laying blame at the doorstep of this website and the design contained therein!

And there it was, standing proudly atop my recently acquired aluminium mast waiting to receive it’s first signals from space. It even survived storm Ciara …

Despite all the effort I put in to produce what I thought at the time was a pretty awesome antenna it never received a thing, bupkis, nada, zero, zilch … empty waterfalls all the way! Early into my investigations of what might have gone wrong I discovered I’d wired the elements out of phase which meant rotating the wire connectors in the top of the antenna tube by 90° … fiddly but simple enough. Great excitement preceded great … disappointment as it still refused to work.

I spent a couple of weeks on and off trying to get to the bottom of the issue, trawling the Libre Space (and other) forums, checking continuity in the antenna, running various tests which had to be on a Linux machine (yet another challenge for someone who’s spent most of his working life supporting Windows!). It just wasn’t to be and the antenna is now sitting up in the roof space of my garage waiting for me to decide what to do with it. I invested a lot of time in the build and I’m loath to scrap it so I might come back to it when time allows.

In the meantime, the story isn’t quite over. Hang on in there for SatNOGS part IV – Return of the Satellite Signal … coming to a screen near you soon!

SatNOGS part II – the slim jim antenna

Before I start, a warning … this isn’t a step by step tutorial on how to make a slim jim antenna, it’s just an insight into how I made mine. I’ll include links to sites and resources where you can get detailed information as I go along.

I think it’s safe to say this is a pretty basic, omni-directional antenna. It’s certainly cheap and easy to make but, like all antennas, you need to keep your dimensions pretty accurate as the relationship between the effective length of the antenna and the wavelength of the signal you want to receive is critical to its operation (even more so with antennas that are used to transmit as well as receive … who remembers messing with SWR meters on their CB radio setup!).

If you haven’t already, swing by the HackSpace website, download yourself a free PDF copy of issue 18 and ‘turn’ to page 110 for a full article by the now almost legendary Mr Jo Hinchliffe! There you’ll find a full list of materials, a proper step-by-step construction guide and some handy links to further information online.

Without further ado, below are a few images outlining my antenna construction …

SatNOGS part I – An Introduction

A while back I wrote a post about my ADS-B setup for tracking aircraft. Around the same time I’d read that it was possible to track and receive signals from satellites but I’d thought it must be far too complicated & involved to do such a thing … until I received my copy of issue 18 of HackSpace magazine that is!

For anyone interested in further reading I’d recommend following the link above and downloading the free PDF file so you can read up a little more on the background to SatNOGS and more detailed information on what is required to setup your own ground station …

  • Information on the Libre Space Foundation which grew from the SatNOGS project can be found on pages 46 & 47
  • If you should feel the urge to create and launch your own small satellite, check out pages 36 – 41
  • How to build a SatNOGS ground station is outlined in pages 42 – 45
  • Making a slim jim antenna (my own experiences will follow in the next post) is described on pages 110 & 111
A little tease, my SatNOGS setup (top) and my PiAware ADS-B setup (bottom)

Incoming …

This project started a few months back when I discovered that USB TV receivers that use a certain chipset are also capable of receiving signals from aircraft. These signals are called ADS-B (Automatic Dependent Surveillance – Broadcast) and are a convenient way for air traffic control (and anyone with a suitable receiver) to monitor an aircraft’s ID, position & vector).  For anyone with an inquisitive nature, there’s a Wikipedia entry with more info here.

I started with a suitable (cheap, I hasten to add) USB DVB-T stick (that’s Digital Video Broadcasting – Terrestrial … basically, this is the modern digital way of beaming TV programmes to houses over the air for all you couch potatoes out there!). Replace the TV aerial with an aerial tuned to receive signals at 1090MHz, which is the frequency ADS-B works at, add some suitable software and you can see aircraft flying in your vicinity overlayed onto an onscreen map.

So I downloaded a couple of Windows packages which I setup on my laptop, plugged in the DVB-T stick, popped the aerial in my hobby room window and hey presto, there be planes … albeit not that many. I read up a little more and discovered that 1090MHz signals propagate very nicely through open air thank you very much, but are stopped dead in their tracks by solid matter like bricks, mortar, etc. I also discovered later on that the cheap indoor aerials aren’t exactly tuned to receive the signals, the antenna being too long. I’m no expert on radio signals but from what I’ve gleaned, the length of an aerial needs to be a ratio of the signal’s wavelength it is designed to receive. This defined the dimensions of the aerial I constructed later on to increase the number of aircraft I could track.

That brings me pretty much up to date. The final piece of the puzzle that triggered a proper setup for aircraft tracking was when I routed a couple of CAT5E cables from the house out to the garage, which gave me a reliable gigabit link back to the house and the ability to install a wireless access point in the garage for all things untethered.

As with a lot of my projects I tried to re-purpose as much as possible as that’s half the fun! The mast for the aerial was made from the centre pole of an old rotary clothes dryer and the brackets were made from sections of a TV wall bracket welded together. The only purchase required was some suitable V bolts to hold the mast to the brackets.

 

Welded bracket
Rough but ready welding!
Mast fastened to finished bracket
Add a little paint …
Brackets & mast in situ

The next step was to construct a suitable aerial and luckily for me there were quite a few options out there … the simplest set of instructions I could find was here via the ‘Your First ADBS Antenna’ PDF link. I had to buy the SO-239 chassis connector ( these accept PL-259 plugs which will be familiar to all those like me who messed with 27MHz AM CB radio back in the day!) but the 1mm copper wire was taken from my collection of twin & earth cable off cuts. The connector is quite a chunky piece of metal so I needed a big soldering iron to apply enough heat to get the solder to flow … luckily for me I had my Grandad’s old Wolf iron. I used it at my peril though, after something like 60 years in existence the insulation is looking a little worse for wear …

My Grandad’s solder ironing is definitely showing its age!

Still, it survived … as did I, and I constructed the aerial ready for it’s new home. The copper wires were trimmed down to 68mm in length once soldered to the connector, this is 1/4 of the 1090MHz wavelength (told you I’d get to it later!). I’m no expert but maybe someone in the know can explain if this is a 1/4 wave aerial with a groundplane, a 1/2 wave dipole or something in between?

SO-239 & 1mm copper
SO-239 connector and lengths of 1mm copper wire.
Ready to start aerial soldering
A quick jig made from a timber offcut and the all important flux pen and soldering iron!
Soldered 1090MHz aerial
The 1mm copper soldered into place.
Finished 1090MHz aerial
The copper trimmed to length and the ground planes bent to 45 degrees … ready to go.

I bought a 5m length of RG58 coax cable terminated in PL259 plugs from eBay to link the aerial down to the receiver. I also bought an inline SO-239 connector (or female PL259 if you will) to MCX plug ‘pigtail’ cable to fit between the main aerial lead and the USB receiver socket. I think if I did this again I’d be inclined to buy the cable and connectors separately and construct my own cable as it would be neater and certainly cheaper.  

After 10-15 minutes of picking through my collection of self tapping screws the aerial was fixed to the top of the mast, the mast mounted back on the brackets and the cable routed down into the garage.

A bucket of bolts (screws)
The boring side of Making!
Aerial on mast
The aerial fixed to the top of the mast. You can just see the RG58 coax cable coming from under the plastic cover.
Finished 1090MHz aerial in situ
The finished aerial aloft its mast and mounted to the end of the garage.

I’m going to skim through some points here as most of the people who follow my blog aren’t looking for step by step instructions for anything I do … they just like to have a window onto all the stuff I get up to! The receiver setup I chose is a very popular one, the software (more an operating system / software package combo really) is called PiAware and as you can probably guess it was written to run on a Raspberry Pi. To keep costs down I purchased a Raspberry Pi Zero W … this is a very cut down (yet still powerful) board which has wireless connectivity. Combined with the gigabit link from my garage back to the house and the wireless access point I’d installed this was the perfect option. I had a spare ATX PC power supply knocking about so this was hacked to provide a 5V supply (plus 3.3V & 12V should the need ever arise) with more than enough current to power the RasPi. An old USB phone charger lead got modified to connect the PC power supply to the RasPi and all the parts were in place.

Raspberry PI zero w
That Eben Upton has done a lot we should thank him for, I can tell you … I give you the Raspberry Pi Zero W
The ADS-B setup being tested
Not all test labs are clean and shiny you know!

To wrap things up, the PiAware installation has an IP address on my home network which I can connect to via a web browser on my laptop and see information about aircraft that are in range. I’ve also created an account on FlightAware which uses the information my setup receives to improve the accuracy of their aircraft positioning information. The RasPi runs without any intervention from me so the information it gathers is passed on 24 hours a day.

PiAware screen
The PiAware screen showing aircraft details.
Coverage 19 Dec - original indoor aerial
Original indoor aerial coverage (window faces roughly WNW)
Coverage 22 Dec - homemade aerial indoors
Original indoor aerial replaced with new homemade item … still indoors
Coverage 23 Dec - homemade aerial in situ on garage
The homemade aerial in it’s new location on the end of the garage.

I struggled with WordPress’ new editor (Gutenberg) on this post so I apologise for the change in layout. That aside I hope you found the post informative / useful / entertaining … or whatever!